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Engine Knock Troubleshooeting (84 vw Jetta)
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RoboDisko
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Dec 20, 2014, 10:57 PM
Post #1 of 20
(2648 views)
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Engine Knock Troubleshooeting (84 vw Jetta)
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Hey everyone.
I've got my great 84 VW Jetta. It's my first car and while I've done a lot of stupid things, I have also learned a lot, and it still seems to run. It's a 1.8L NA mechanically fuel injected (K-Jet) with 240K miles.
Ok so my latest problem that I have not been able to solve through Google is a bit of an engine knock. I'm not certain if it is predetonation or knock or what, but I will refer to it as engine knock.
I'm going to try and throw as much information as I can into this, and it may get messy at points. Sorry bout that...
Symptoms:
This knock only occurs at low engine load and low RPM's. I don't think I have ever had it over 1500 rpm, regardless of throttle point. The exact throttle point at which it occurs seems to vary every time I run it a little, and in general, it seems as though it is getting higher (stops occurring at a higher throttle point) (I use a vacuum gauge to monitor the throttle point). For example, sometimes it does not occur at my 25mph 5th gear cruising @~1400rpm, and other times it does. If it is occurring, I can bump the throttle and it will stop occurring, but will usually start occurring again when I go back under the threshold throttle point. Engine temperature seems to have some effect on the throttle point at which the knock occurs, but I have not made a definitive link between oil/coolant temperature and the threshold throttle point. This knock seems to also occur at idle, but at idle it is very consistent and less pronounced, whereas if it happens while moving it is much more noticeable and less consistent.
Background:
This started the first time I ran my car after "project miserable" (just made that name up for it lol). One of the exhaust studs for my recently installed aftermarket exhaust header had come loose and cause a large exhaust leak. In attempting to tighten it, the stud sheared off. One Saturday I blindly decided to fix it, thinking i could have it repaired in a few hours. That was October 25th. Once I got it off I noticed I needed a new exhaust gasket, and wasn't going to have it running that day. Then I got a stud puller, which worked great, but stupidly sheared off 2 studs inside the head. Tried a screw extractor, it broke of course. Drilled them out with much difficulty, but I punctured a water line in the head. Tap kit, RTV silicone, loctite red, coolant, distilled water, blah blah blah. On November 8th, I finally got the thing running again, with approximately $130 in tools and disposables, and way way too many hours, just to fix a simple exhaust leak. Ok so that was "project miserable." After that, the knock has been occurring to some degree. I think the knock probably occurred to a lesser degree before "project miserable", but I think I thought it was the exhaust leak. ( it was a large exhaust leak) It was after "project miserable" that the knock became distinctive and problematic.
Since then, I have ran some "Chevron Techron Concentrate Plus" though the fuel system, which does not seem to have had a meaningful impact on the engine knock. Compression on this engine was recently tested at ~150psi on #1-3, and 110 on #4
My thoughts:
I think the low cylinder compression on #4 is related to this engine knock. I also think the low compression on #4 is likely related to the exhaust leak from "project miserable", because the exhaust leak was on #4. The header and head had separated enough that, at the right angle, I could see occasional flame between the head and header. So, I'm kind of thinking the the valve may have been affected by cold air quickly finding its way to the hot valve, and causing it to seat poorly. However, I am not sure how a poorly seated valve could cause the "knocking" in the way I have explained it. I am considering doing a valve job, but I do not want to do a valve job if this issue persists afterwards. I would like to know what is causing this abnormal knocking so that I can repair my engine properly.
I hope the information I have included is comprehensible. Thank you for you interest in helping me fix my awesome car :)
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Tom Greenleaf
Ultimate Carjunky
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Dec 21, 2014, 1:11 AM
Post #2 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Google or other search out diagnosing engine noises and how to diagnose: I'll lay out some.........
Just at idle speed or other without load:
Ticking or a dull or hard knock, muffled bell sound, double knocks or rattles for some.
Double knocks are usually wrist pins, single harder knocks are bearings, ticking is valve train parts broken or loose something each on their own. That's primal for a beginning.
Now no load knocks you generally rule out detonation. When listening with or without a listening rod or stethoscope as needed you cancel one cylinder at a time and see what changes about the sound. If worse note it and it goes away note that.
You compression, age and miles is about fatal if accurate so don't get too excited about this car sorry to say.
Please, what is a 1.8L NA for an engine? Mechanical fuel injectors? Not my cars but thought those were almost gone be the 60s never mind 80s.
Record noises if you want and try to post. Most experienced techs would just hear something, recognize type and quickly move to isolate what might be. It's when not familiar you struggle and I'm at a loss as noise diagnostics on a chart is available but didn't find it quickly - sorry.
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You first car and appreciate you are excited. Just be realistic. Compression test I'd like to see both wet and dry results then a leak down test and get low cylinder on TDC and force air into it somehow noting where it comes out, thru exhaust or intake.
The web and forums may not be you best help. Real tech right there or bring it to one and find out if this noise is fatal or not or at least if a strong clue as to what.
Friendly suggestion is to keep your investment low on this and do more learning that getting way too much hope up that if this car by miles alone is going to be a dependable driver again it probably will be way too costly and extensive all around never mind just the engine,
T
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Tom Greenleaf
Ultimate Carjunky
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Dec 21, 2014, 4:11 AM
Post #3 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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New post to expound on engine noises. Note that "experience" in the tone of the noise becomes key. Note again that when noise is a wrist pin or rod knock and engine has over 70,000 miles (that can be off quite a bit for what is said below) it usually isn't worth fixing that engine but you would sooner be looking for another engine or another vehicle just as cost wipes out any possible value. Please disregard what people will do for super rare antiques and unique cars when cost is no issue.
Comments and thoughts from another below this line below my comments.
Specific to your car you already know something is way of on one of 4 cylinders compression wise, plus this vehicle is both now at least 31 years old with well over 200,000 miles or so it says? Alone not always a problem with surreal attention to kept/stored, serviced, driving habits and more plus quality of products for routine maintenance and of course throw in good luck as some perfect engine are lost to sudden oil loss from assorted things like a failure of even a drain plug, oil filter other oil sealing parts up to road debris striking a part in just the wrong place like an oil pan and loss of oil so instant you barely have the time to shut down.
At the miles on this particular car it would be unusual to have a total known history from new which may have already included replacing the engine new, used or a total rebuild. My opinion is that a rebuilt engine with almost no exception will have the life expectancy of one new and truly good when new. Not all are that perfect new simply as they are made machined parts the tooling wears so no two are quite exactly the same.
It's my experience that most truly defective engine will show up right away new or soon after then it's the care along the way plus the original design for a life expectancy as well. Happy reading.........
T
________________________________________________________
 You might not have enough money to send your kid to college after you spend it fixing an audio illusion. On the other hand you may spend dozens of hours and hundreds of dollars replacing parts in an engine that is truly shot.
First thing you need to do is spend 20 bucks for a cheap stethoscope at the auto parts store or if you are going to do this a lot get the electronic ones from Steelman for about $160.But, possessing human nature, you will convince yourself that a hose stuck in your uneducated ear will do just as well. No sense in arguing with you that the whole idea is to be able to discern infinitesimal changes in direction and intensity that require the use of two somewhat experienced ears AND the right tools.
So stick your dumb ol' hose in your stupid ol' ear and we'll start with some clues.
Remember that diagnosis of engine noises is nothing more than splitting possibilities down to only one
First off, eliminate all of the accessories like the alternator, power steering pump, A. C. compressor and vacuum pump by removing the belts one at a time. If the noise is gone, of course the problem is a belt driven accessory. If the naughty noise is still there you should be able to hear it more clearly by not having the accessories whirring away.
If the engine has a carburetor instead of fuel injection it probably has a mechanical fuel pump mounted to the engine. Before the engine gets too hot, put your hand on it. If it is making a noise you should be able to feel it.
Try to track the noise down with the stethoscope tip or the end of the hose suckered onto the engine surface, sealing the end. Spend a full ten minutes putting the hose all over the engine, not just where it is loudest. Try to envision the parts moving inside the engine. You are training your ear, not just listening, so don't get in a big rush except to be sure that the engine doesn't overheat. A trained ear can tell you which piston is slapping or which rocker arm is clacking from outside the engine so if you come out from under the car proudly saying, "it's the bottom end" get your Dumb-Ass back under there until you can tell me it's coming from the oil pump or the 3rd piston back on the driver's side or the flywheel or the camshaft.
Rod knocks are loudest at higher speeds (over 2500 RPM) Feathering the gas pedal may result in a distinctive back rattle between 2500 and 3500 RPMs.
Bad rod knocks may double knock if enough rod bearing material has been worn away allowing the piston to whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) klock sound.
Wrist pin knock in modern engines is very rare today but is a favorite for the misdiagnosticians.
Determining which cylinder contains the noisy parts may be aided by shorting out the plug wires one by one with a common low voltage test light. Now you won't get the bulb to light up but it is a convenient way to short the cylinders without getting zapped or damaging the ignition coil.
Attach the alligator clip to a convenient ground, away from fuel system components, and pierce the wire boots at the coilpack or distributor end of the wire.
Some guys will use straight pins stuck in the ankle of the wire boots in the distributor. You know. The guys with tattoos and key rings stuck in their eyebrows. Then they touch a grounded jumper wire to each one. If the noise is changed when the plug wire is shorted to ground, you can figure that the problem is in the reciprocating bottom end parts. (piston, wrist pin, connecting rod or connecting rod bearing) The reason the sound changes is that when you short the cylinder plug wire you are stopping the combustion chamber explosions that are slamming the piston downward making the inside of the big end of the connecting rod bang against it's connecting rod journal. Or in the case of piston slap, no explosion changes how the piston is shoved hard sideways against the cylinder wall.
If you get a change in the sound when you short a cylinder out it may become moot as to what the problem is because the oil pan and cylinder head must be removed to correct the problem. [Generally speaking, an engine with damage to reciprocating parts (pistons, rings, connecting rods, wrist pins or rod bearings) and more than 70 thousand miles is not cost effective or risk free enough to attempt to repair. Replacing a crankshaft, for example while the rest of the engine has 70k perfectly maintained miles on it is risky enough but whatever killed the crank has scored the rings and packed the lifters with debris and smoked the piston pin bosses etc.
If the sound doesn't change, look at parts other than the reciprocating ones. In many cases of rod-knock or piston slap, more than one is banging so even if you eliminate the noise from one rod the other one will still be a-banging away with a different, more singular tone.
Valve train noises generally are loudest up to 1500 rpms. Lifters are also misdiagnosed commonly as the source of many noises when in reality they are quite trouble free, sorta. Dirt contamination on a sludged engine is the number one cause of true lifter noises, low oil pressure is number two, . Whatever you do, don't put engine flush in a sludged engine! We call it "Instant rod knock" because of the way it overloads the oil filter to the point of opening the filter bypass valve, flooding and destroying the engine bearings with mud. The only safe way to clean a sludged engine is to accelerate the oil changes and let the detergent in the oil do the cleaning at a controlled rate. Like every 500 miles
By the way, if you have low oil pressure, don't bother putzing around with the valve train because the damage you find will be the result of low oil pressure and will return after you spend a bunch of money on valve train parts.
Over nineteen engines out of twenty that we tear down with low oil pressure do NOT have bad oil pumps but have worn out bearings and journals so quit with the wishful thinking about just putting a pump in it.
Think about it, usually, an oil pump is two dumb ol' iron gears spinning around immersed completely in oil. EVERYTHING else in the engine has a tougher time of it than the oil pump.
Worn camshafts, low oil pressure, worn rocker pivots, very loose valve guides, worn rocker arms…..
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RoboDisko
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Dec 24, 2014, 1:17 PM
Post #4 of 20
(2595 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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What is 1.8L NA for an engine? I forgot to mention that it was sohc 8v :) Well actually, this was the "big engine" for this particular vehicle, other options for this vehicle include a 1.1L with a carb. And the vehicle weighs little enough that the engine has no trouble moving it around quickly enough. I try to squeeze mpg out of it so the engine's displacement is great for that.
I've been paying more attention to the knock lately, and it seems to be very unpredictable. Yesterday, I drove 6 miles, and when I got there it was idling without the knock, which lead me to believe it went away when warm. About an hour later I drove 6 miles back to my house, and when I got there the knock was louder than normal, which is just confusing. So I recorded it.
https://www.youtube.com/watch?v=cpJBKqdMrmA
As you can see in the video, the knock goes away as soon as I find the traction point on the clutch. It also goes away if revved a little bit. There is a higher pitched noise that you can hear in the video a few times when I let off of the clutch a little too much, disregard that noise. That noise is just something in the dash vibrating in a harmonic frequency to the engine rpm.
FYI I put mid grade fuel in it once, at it had no noticeable impact on the knock. The fuel in it right now has chevron techron concentrate plus fuel additive, which doesn't seem to have had any meaningful impact on the knock either.
I have been trying to keep my investments low on this car, but I would like to get it running right so that I can put more money into it without as much risk. As for the wet/dry compression tests, I will get to those soon hopefully. Also looking into getting an automotive stethoscope.
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Tom Greenleaf
Ultimate Carjunky
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Dec 24, 2014, 1:46 PM
Post #5 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Dash knocks! That's special.
Nice job with the video. Inconclusive still. Could actually use someone doing what you are doing and another listening under the hood.
Kinda seems like ONE cylinder. You could try canelling them one at a time and check anything about that cylinder.
Forgot already but you know even a loose spark plug can make noise but much more often right after they are installed and something went wrong.
Stethoscope: Best of course. I can use a long screwdriver (AYOR) and find most bearing noises no problem. Untested my me but a stretch of hose or a long funnel has been mentioned by some for ways too.
If you want to speed up finding it and know fast if harmful (possible) or what it most likely is have a tech check it out.
If this is low oil pressure or flopping belt/chain to cams it could be a disaster. Other is right when you expect it is with service belt(s) off and quick (don't do that for long) check if it can't make the noise and check all drivin by belts on it.
It's totally worth finding out IMO,
T
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Discretesignals
Ultimate Carjunky
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Dec 24, 2014, 5:11 PM
Post #6 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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If you watch his foot when he engages the clutch, it goes away. Could be something going on with the clutch release bearing. Might have to get the vehicle in the air to see if you pinpoint the source. It doesn't sound like something from the engine unless it is the exhaust beating on the floor. If it was something in the engine knocking, the knocking would increase in frequency with the rpm of the engine.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 24, 2014, 5:13 PM)
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Tom Greenleaf
Ultimate Carjunky
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Dec 24, 2014, 10:29 PM
Post #7 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Good point - may not be "engine" at all but trans something or clutch T/O bearing or linkage to it. Dash noise was noted earlier so suggestive of generally not isolating engine/trans well like maybe motor mounts?
Noted: Noise when just a little drag from releasing clutch goes away but not really loading down engine. All lash* in clutch linkage all along the way from where it pivots inside on to trans would probably tighten up.
* "lash" I mean like any loose parts would have pressure on them without free-play -- kind of like a chain is loose until you pull on it the links all touch.
If two people looking and creating this while watching bet it could be found in no time,
T
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RoboDisko
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Dec 27, 2014, 11:01 AM
Post #8 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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I tend to think it is the engine, not the clutch or anything else down stream, because when the vehicle is moving and the throttle is relatively low, sometimes the vehicle will jerk in a forward and back motion. Sometimes it is worse than other times, and any time it does this I can make it stop by increasing the throttle (pushing the gas pedal more) However, I would not completely rule out that it is the clutch/trans.
Anyways, what should I do to trace down the problem from here? Is an automotive stethoscope a must? If so, I can order it and have it here around Tuesday. If not, what do you suggest I do first?
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Tom Greenleaf
Ultimate Carjunky
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Dec 27, 2014, 11:47 AM
Post #9 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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You can find noises with a listening rod and avoid buying the stethoscope. I listened again and again to the video you made note it doesn't take much to make it go away either light load or doesn't do it at higher RPM if also more load so??
May not be actual engine at all but perhaps motor mounts, loose something, exhaust parts and connections.
It might help a lot if someone could listen and someone cause the noise. Other is plain test for loose things prying carefully or by hand/glove it hot even with engine off and cold. Tap on exhaust with a rubber hammer or even piece of wood might make the noise.
Is everything to do with air intake parts all intact as well?
Watch motor mounts when under load, wheels blocked, parking brake on hard and nothing in the way with a helper or other test method if you can't do that safely.
Noises are tough when not right there.
It's interesting that the light load when you are releasing the clutch does seem to make it go away and from here does make the clutch and trans parts on the list.
It's tough. Might need a pro to hear it in person with some suggestions?
T
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RoboDisko
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Jan 5, 2015, 10:00 PM
Post #10 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Ok turns out we have not one problem but 2.
The main problem that I have been focusing on has been the noise when idling. I thought the knock when moving was linked to the knock sound when idling, so I have been focusing on troubleshooting it at idle.
I was looking around the engine with a screwdriver, and wasn't having a ton of luck. I put my hand on the intake manifold with a little bit of pressure, and it stopped! So yea...engine mount. The vibrations from the apparently failing engine mount were then amplified by the chassis into what sounded (to me) like an engine knock. The clutch must have put just enough tension on the engine to make it stop as well. I traced a little more, and I'm pretty sure I know which engine mount it is. I'm not too worried about this noise anymore :) I'll probably replace the engine mount eventually.
Before I found that, I replaced random auto lite spark plugs I had in the engine with a recommended triple electrode non-resistor NGK plug for the engine, and did a full wet/dry compression test. We'll get to the compression test in a bit. The spark plugs seemed to have a noticeable effect, with the engine seeming to run smoother at idle. Even though it's off topic, I have to say I didn't realize how awesome my car is to work on. We were having some oil issues on the family vehicle, 08 suburban. I wanted to run a compression test mostly to get a general idea of the engine's health. I think I am exaggerating a little, but it took about an hour just to get the spark plug WIRES off. We couldn't even access one of the spark plugs because the engine was sunk into the firewall so that it had maybe an inch of extremely hard to reach clearance. Are you supposed to pull the engine to replace the plugs on this kind of engine? Just ridiculous. For comparison, I completed the full wet/dry compression test and spark plug replacement on my car, by myself, in under an hour, at a leisurely pace.
Ok so the 2nd problem, the knock while moving, MIGHT also be the engine mount, but it is a lot louder and less consistent than the idle knock was. With the new spark plugs and such it seems to be less common, to the point that I'm not sure if it is an engine problem or a driver problem. I managed to get it to occur by bringing the rpm down to about 600 while trying to accelerate. (video:https://www.youtube.com/...7nsfaHVmjU3LQgKTckeg) This seems to happen to a lesser extent at more normal rpms (1-2k), seems to happen when you first try to accelerate, or after shifting to a lower rpm in that range, but usually goes away after only a few "knocks," often as few as only once. I'm not too worried about this right now, as by keeping the rpms a little higher seems to make it go away, but I wouldn't mind some professional advice on what it could be.
Ok so the promised wet/dry compression test results.
These were performed on a cool engine (the engine head was comfortably warm) wet results were attained by adding about 2 teaspoons of used 5w-30 engine oil with engine oil flush in it from a certain suburban. (It was quite thin for engine oil, which I think is ideal for compression tests)
1 dry:155
2 dry:148
3 dry:155
4 dry:135
1 wet:184 (+29)
2 wet:175 (+27)
3 wet:179 (+24)
4 wet:154 (+19)
Ok, my non expert interpretation of this data is that cylinder 4 has poor valve seat that is causing it to have poorer compression that the other 4, but they all need new rings. (pretty badly?)
I would like to shift the focus on this thread a little bit. I anticipate doing some deeper engine repair on my engine soon. I was leaning toward doing a valve job, but the wet numbers have brought me into needing to re-evaluate what I anticipate doing. I want to do this because 1. I want more engine efficiency (mpg), 2. I want more performance, 3. It's fun and educational, 4. I wouldn't mind more engine life, and 5. It's my car's 31st birthday this month! And, on this particular vehicle, I have very little to lose in the event I screw up. I have already purchased a service manual for this vehicle. I feel like with the service manual, the internet, your help, a lot of time, and a bit of cash, I should be able to successfully perform the deeper engine repairs.
I would like some advice as to what I should do in my deeper engine repair. I don't know if I'm ready to go all out on this, and do the top and bottom at the same time. However, if the bottom needs it, it would be logical to do it while the head is off, wouldn't it? So, based on your knowledge/experience, should I do just the top or bottom, or should I just go all out on it? Should I replace the crank bearings? Do you think I should even be attempting this deeper repair at all? How much should I expect to be throwing at this project in tools/parts? (I have a good socket set, and other common things like allen wrenches and even circlip pliers, but I know I'll need specific things like valve lashing tool, ring compressor ...) I was wanting to boost the CR a little bit to increase the efficiency, but simply fixing the cylinder rings would probably do a lot more good.
What do you think?
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Tom Greenleaf
Ultimate Carjunky
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Jan 6, 2015, 12:10 AM
Post #11 of 20
(2483 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Wow - I thought I was the verbose one - no problem.
Now some random thoughts on this: #1 - Quit using non OE and multiple electrode plugs especially unless they were in fact OE for some reason. Multiple electrodes can't both fire so chances of one fouling is tons higher, cold misfire and then compression testing off. Lose, lose, lose situation. Plugs to close to get to you meant Suburban? You lack proper tools as those are easy. Others are a royal pain on assorted engines you might tilt engines or more? If you struggled that much just removing plug wires you probably wrecked them also.
Your cylinder number 4 suggests more than just worn lower end so yes valves but more tests to be sure exactly what that may require taking head off but wait on that. It has too many miles IMO to play with at this point short of some reasonable way to just raise idle speed a bit (100 or so RPM) which may not be possible on the VW. In short doing a valve job on this may fix the problem very short term but both costly and other things may pop up showing the age and wear that exceeds this exact problem. No harm at all in learning and some includes wasting lots of money and wrecking something best left alone. A long run with mounts fixed may improve valves some? May not be valve themselves at all either but guides or other flaws?
Find which motor mount either by watching while engine has more torque applied with a helper or lifting (wood can work sometimes) in the right manner and watch which one or more is the culprit. Wild noises can happen when engine a metal really touch no longer isolated by rubber.
VW again: How much do you want to lose for $$ in learning on an engine that has enough miles and time already for nothing?
Lower bucks approach IMO would be correct plugs, and top shelf synthetic oil of exact specified viscosity you may get it to run well for a good bit longer or not.
Hey - learning costs no matter what. Just don't want you to waste too much on learning the hard way on the VW,
T
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RoboDisko
User
Jan 6, 2015, 7:59 PM
Post #12 of 20
(2461 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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(this post is in chronological order response to Tom Greenleaf)
"Single or triple? Resistor or non-resistor? All are listed in your owner's manual. Either will work; choose which one works best with your car." (from cabby-info.com, which is the same engine and i use this site extensively for engine info)
The plugs I have are an OEM suggested plug for my car.
The hour spent working on the wires in the suburban was a big exaggeration... probably 15 minutes? Still a big pain. My point was that I didn't realize engines could be so hard to work on.
This car is 31 years old. There is no "engine computer" or "digital idle stabilizer" and thus the idle is completely mechanical and completely adjustable. Where it is at now is OEM suggested, so I don't really want to raise it just because of a bad mount.
WAIT, the motor mounts will affect the valves? I don't see how a motor mount letting excessive vibrations into the cabin will have a meaningful impact on the valves, so please clarify on this.
Using a screw driver, like you suggested, I am reasonably certain I know which motor mount is done. It is quite bothersome, and while it went down on my priority list after i found out it was just a mount, I will be fixing it soon enough.
Found this on cabby-info lol:
"Symptoms of Mount Failure:
When motor mounts fail, the engine and transmission will rock causing very noticeable vibrations inside the passenger compartment (especially at idle), shifting issues, exhaust damage, and more."
I have already taken your "lower bucks approach." Except the OEM oil viscosity for this engine is very vague. In the manual they give a chart based on temperature. Cabby-info says this:
"OIL
This can be quite controversial; positive and negative comments are said about all oil types and brands. Most agreed upon, however, is using 20W-50 in the warm summer months and 10W-30 in the cold winter months, or 15W-40 year-round (those in year-round warm climates can use 20W50 year-round)."
Anyways, I run Pennzoil ultra platinum (the good stuff made from natural gas) 5w-30. I know it's a bit lower than OEM recommended, but I figure even though it is lower viscosity, it probably does a better job then 10w-40, or SAE 30, did in 1984 while being thinner for better fuel efficiency. Anyways, I like to think of it as being the best oil available at the moment. Using thicker oil than diesels in this engine seems like overkill to me.
Right now I am wondering valve job vs full engine overhaul. Pros and cons on this engine?
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Tom Greenleaf
Ultimate Carjunky
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Jan 6, 2015, 11:41 PM
Post #15 of 20
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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1984 is plenty NEW enough for electronic snags just fewer. Get single electrode plugs. Whoever thinks a spark plug will strike more than one at a time or twice needs mental help! It will only fire on one and the other foul up the show.
Screwdriver trick for noise if fine but not for motor mounts. Those you see by eyes! You need to either support engine under oil pan with nice soft wood in just the right spot(s) with a floor jack OR have some competent help with someone (brake standing) meaning fight the car against itself and it's own brakes/blocks on wheels just enough to see which one(s) lift. Mounts are just metal with rubber glued in between and will separate and shouldn't. When they can't hold within those limits then the problems come out.
Hey - cars are heavy and you need to use your head with what you might do or try so you don't get killed or hurt yourself or someone else or plain don't do this stuff.
If this car is in such lousy general shape you'll harm things with normal checks then it's not worth it now at all.
Stop playing with oil viscosities. That went out with the wooden wheel and trust me I was fixing those too!
T
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RoboDisko
User
Jan 10, 2015, 11:18 PM
Post #16 of 20
(2417 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Yes, it does have a few electronic controls. The k-jet unit is the most advanced one. It controls the fuel/air ratio, and I'm pretty sure the engine would still run without it. Also a big transistor for the electronic ignition, the fuel pumps, and a few electrically heated-controlled valves for cold enrichment and warm up idle regulation. Other than that, everything is mechanical. And most of the electronics in it are very simple to override, if desired.
The triple electrode plugs ARE suggested for this engine and ARE working better than the old ones. If I ever need new plugs, I'll probably try the single electrode non resistor plug for it. But lets think about these triple-electrode plugs for a minute. It is not physically impossible for multiple gaps to become ionized at the same time, although I would expect it to be very unlikely. What I find likely is one of the electrodes to become preferred, and the other 2 will foul up. This DOESN'T MATTER, because the electrode in use is not fouled. Right? After a while, the gap will wear down and the spark will burn through the carbon and find a new preference electrode. So having 3 electrodes just gives be roughly 3X longer theoretical plug life. The only other difference is the angle of the spark. On a single, the electrode blocks the combustion process from traveling immediately towards the piston. A multi does not. Will it make a meaningful difference? Probably not. However, a triple electrode plug is not inherently inferior, and in my application it is working better than the single electrode plugs were, and I AM NOT getting new plugs in the immediate future.
I've already ID'd the engine mount and ordered another.
This car still runs fine. I can still pull off 34mpg on the highway with it, which is ~30% higher than the EPA when new, (26mpg) and better than many cars on the road. I am simply asking if is should anticipate a valve job or a full engine overhaul.
At this point I am leaning towards a valve job, because a full engine job will take a lot more effort and $$$. The cheapest ring set for this I have found so far is $90. That is more than I really want to pay for the whole thing I want to do, and definitely isn't the only thing I would need.
On the flip side, A valve job should bring all of my cylinders up to roughly the same compression, and needs a lot less tools. It is also less over my head than a full overhaul is at the moment.
Should I worry about the rings? By the time I got a new set of rings seated, would the compression be any higher than it is now?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 11, 2015, 4:01 AM
Post #17 of 20
(2410 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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Would you please stop and listen for a bit? Quit playing with plugs. Only a couple engines require multiple electrodes and it wasn't this one. Use only what it called for. IF you defeat plug resistance you just create a monster. Correct plug would almost always be a Bosch like this..........
 Price: $2.29 This fits this vehicle.
- Part Number: 7900
- Notes: Gap is pre-set. Do not gap.
__________________________________
No multiple electrodes. Spark is only going to the one with the least resistance only and any others just get fouled and can become the least resistant and not fire at all really messing you up - quit it! That cylinder might run cold then compression testing is not just a test but could lead you to wrong conclusions.
Arguable on doing up the head. If you get an old engine such as this and head is perfect and lower end still with just normal wear it puts stresses on that so may be a waste. "May" is the operative word. Why on earth are you even discussing fuel mileage at this point? Fuel isn't even what was sold when this car was new and unless that was the whole issue you came here about forget that. You'll spend more wasting $$ on wrong parts up to wrecking this thing long before you'll need to worry about gas mileage as a cost factor,
T
(This post was edited by Tom Greenleaf on Jan 11, 2015, 4:39 AM)
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RoboDisko
User
Jan 12, 2015, 8:44 PM
Post #18 of 20
(2387 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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The plugs I have in it are suggested, and they are not causing any issues at the moment. If they start causing misfires from a short or something, I will notice it very quickly. If I ever need new plugs for this car, I will most likely get not resistor single electrodes. As of now, they are running better than the older plugs I had in it, and thus they are staying for now. In addition, the compression test was ran before switching to these plugs.
Just for reference, this is copy/pasted from (links of that sort not allowed)
"Single or triple? Resistor or non-resistor? All are listed in your owner's manual. Either will work; choose which one works best with your car.
Bosch no longer makes good spark plugs; Champions are good, but NGKs are best.
"Use BP6ET and nothing else" is often said to folks whose cars fail emissions tests. Bottom line is this: ANY new plug you install will be better than the old ones in the car. And again, use what works best with your car; my '86 does not like triple, non-resistor platinums, it prefers resistor single platinums or coppers; the opposite could be true for your car."
I trust that website more than you fyi. I don't want to argue about plugs anymore, I want to move on.
I was driving my car earlier today. I have a vacuum gauge installed on it so I can keep an eye on engine health and fuel consumption. It has had a bit of a rattle under certain driving conditions (like low rpms under load). I though since I installed it that there was something loose in it rattling, but I realized today that it was most likely a rapid fluctuations in engine vacuum that was being amplified by the gauge into an audible rattle. I am also thinking that these rapid fluctuations in vacuum are probably caused by a leaky intake valve. Do you find this conclusion valid?
FYI typical engine vacuum on my engine is 14 in HG on a cold idle up to 17 in HG on a hot engine, and 13-14 in HG at most cruising speeds when warm.
I should mention that I'm not interested in mpg for saving money, but mostly as an accomplishment. I really want to get 40mpg out of this car, and I think I'm getting pretty close. I also like performance when it doesn't compromise on engine efficiency. (who doesn't?)
(This post was edited by Tom Greenleaf on Jan 13, 2015, 2:13 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 13, 2015, 3:19 AM
Post #20 of 20
(2379 views)
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Re: Engine Knock Troubleshooeting (84 vw Jetta)
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No links please for other than pics or things you did.
Plugs: Use what it called for. I don't care what the twit with green hair said at some parts store that specializes in magic in a can, LED mud flaps and cup holders.
The only good reason for more than one electrode is/was on some when you can't index a plug that would need that it might make sense. It can only FIRE ONE at a time, always the easiest to ground. If fouled it may choose the fouled one and not spark at all but takes the current.
Bosch is probably made in China or perhaps Japan - don't know but Euro cars like what was called for like most not tricks.
Resistor plugs and or wires are for a reason. If you deviate that you'll find the thing may not run at all.
Your site with the Hg tests are incomplete at best and plain wrong so far. Forget that junk and go buy a real e-book or a paper book on principle's of how it works that begins with the crudest way an "internal combustion engine, four stroke, gasoline" works. All the changes since the first are just improvement on that same old principle.
Compression will change cold vs warm and testing is done when warm, all plugs out and throttle held open then quickly again with a squirt of oil. Other ways are needed for some. Hg (inches of mercury) is dependent on your elevation, health of the engine in general and a good diagnostic tool as well. Cancelling cylinders is another or if equipment available cylinder balance on a scope can show how much each contributes to the show.
General: Beware of trick anything out there. The motivation is to sell product without regard if it works or not just sell it. If these tricks were all so great there's no question the original would have used them.
Learn from this car but I suggest not overspending on it. It's not just an engine but the whole car has gone that many miles too,
T
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Please Help - Knock sound & engine fail
