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94 S-10 Blazer loss of acceleration
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Sam77
Novice
Jan 7, 2009, 9:42 AM
Post #1 of 11
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94 S-10 Blazer loss of acceleration
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About 5 months ago I bought a 1994 S-10 Blazer with a 4.3L Vortec engine code W, 4 wheel drive, auto transmission with roughly 166,000 miles. It wouldn't start and after checking fuel pressure found out the fuel pump wasn't working. I went ahead and bought a new AC/Delco pump, pulsator, strainer, electrical connector w/pigtail, sending unit, dist. cap, rotor, plugs and wires, 2 fuel filters, changed engine oil and filter replaced the exhaust from the cat convertor back (old muffler and exhaust was rusted badly). Dropped the fuel tank and cleaned it out and installed the pump and sending unit. Put the tank back in the vehicle, installed one of the new fuel filters in the fuel line and put all the ignition stuff I bought in it. Put a fuel pressure gauge on it and made sure everything was working. I had fuel to the pressure gauge at the schrader valve so it seemed I was ready to fire it up. I tried that and it wouldn't start. I had hot blue spark but no fuel was getting to the plugs. I read in my manual that any problems found with the CMFI unit the entire assembly should be replaced. Well I was short on cash so I pulled the upper plenum and took the unit out, sprayed carb cleaner in the poppet valves and rusty nasty smelling fuel came out. Used some air (low) and blew everything dry and reinstalled it. Put on a new plenum gasket and bolted everything back together. After everything was bolted down and electrical connectors were back together I got in turned the key and within a few cranks of the engine it fired up. I let it warm up while I cleaned up the shop and took it for a drive. Everything was working fine. Drove it everyday to work for just over 4,000 miles then one day on the way home on the highway going up a hill I noticed I was losing power. Never did die but I had to step lightly on the peddle. Anymore than that and the engine rpm's fell. I made it home and when the weekend came I took it back out to the shop and decided to do some testing. Didn't know about this forum but I had the repair manual.....heck I can fix this myself...yeah right. I read in the manual that if the fuel pressure didn't approach 61lbs. on acceleration that the pressure regulator on the CMFI unit was bad and it should be replaced and this past weekend I replaced it. Well after doing some further reading I found out that its a good idea to replace the fuel line assembly (nut kit). I didn't do that and I really didn't look over the plenum to see if there was any wash. Well it's still doing the same thing it was doing. I put a fuel pressure gauge on the schrader valve and here is what I found out. With the key on/engine off and the fuel pump running I have 60lbs. as soon as the pump shuts off the pressure drops to 58lbs but within a couple seconds climbs back up to 60lbs. I turned the key off and let everything set for 10 minutes and the fuel pressure then was 58lbs. I started the engine and the pressure was between 51lbs. and 58lbs. (needle was fluttering back and forth). I increased the throttle to 2,000 rpm's and the pressure gauge needle flutters between 49 and 60lbs. Around 2500 rpm's and the engine starts to cut out, bog down or whatever. It won't throttle up anymore than that. It starts good and idles good and I can drive it in town but I can't take it out on the highway. I put a vacumn gauge on it and at idle it has 19 lbs/inches? and if I increase the throttle it increases to around 21 or 22 lbs/inches. I didn't pinch the return fuel line to see what would happen to the fuel pressure but I think I performed everything else. I'm really leaning towards replacing the fuel line assembly (nut kit) like I should have done when I replaced the CMFI unit. All the fuel pressure readings stay the same with the engine cold or when it's at operating temp. What do you guys think? Where should I go from here? Sure would appreciate any help you can give me. Sorry for the long winded post but I wanted you to know what all I've done.
Also wondering what would make the fuel pressure gauge needle flutter? Don't believe it's supposed to do that.
(hyperlinks removed)
(This post was edited by Tom Greenleaf on Jan 7, 2009, 3:38 PM)
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Loren Champlain Sr
Veteran
/ Moderator
Jan 7, 2009, 5:37 PM
Post #2 of 11
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Re: 94 S-10 Blazer loss of acceleration
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What does the fuel pressure look like with the vacuum disconnected at the pressure regulator? Should be stable, then. If the engine is running lean or rough, the vacuum will be unstable and that will affect the regulator. The Vortecs are know for the fuel feed lines leaking and also the poppet valves on the injectors. If the pressure is stable, although high, with the regulator disconnected, I'd at least 'try' cleaning the injectors/poppets. If you have the capability, I'd take a gas reading of the intake after sitting to see if you have a high CO/HC reading. That should tell you if you have a fuel 'leak'. We've 'fixed' many a poppet leak with cleaning. The "injector cleaner" in a can, IMO, is snake oil. I suppose it's okay for in-between cleanings, but have them cleaned professionally if everything else checks out.
Loren
SW Washington
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Sam77
Novice
Jan 7, 2009, 9:58 PM
Post #3 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Loren
Thank you for the reply and advice. I really do appreciate it.
Unfortunately the fuel pressure regulator is attached to the CPI unit under the plenum (upper intake manifold) and has no vacumn line to it so I can't do anything with it. The CPI itself has an electrical connector.
I just replaced the CPI unit so its brand new. The poppet valves also were attached to the CPI so they're new also.
The engine idles perfect and it runs great up to around 2500 rpm's and thats where it starts cutting out or bogging out. It's not hard to start nor does it die even if I hold the throttle pedal to the floor. Just no acceleration.
I went to the parts store and ordered a new fuel line assembly (nut kit..both intake and return lines inside the plenum that fasten onto the hard lines on the outside of the intake manifold) and also ordered the injector electrical connector and another plenum gasket.
I'm going to go ahead and install them and see what happens. Hopefully that will solve my problem.
If not then at least I will know that everything under the plenum (intake manifold) should be good to go.
I will post back here my findings on what happens when I get that done in the next day or two.
Thank you again for your help.
Sam
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 8, 2009, 12:43 AM
Post #4 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Sam - no harm intended but for goodness sakes try to separate your thoughts! I've never seen such a run on paragraph in web history!
Ok: Two bits out of all of this. The subject line and a vacuum reading.
22hg at a raised idle when 19hg was the baseline suggests your reading was a "venturi" effect vacuum port not 'manifold actual pressure' -- now get an actual vacuum reading and read it at 2,000 rpm held steady.
This smacks of a restricted exhaust or that you are working on it at about 1 to 2 thousand feet below sea level,
T
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Sam77
Novice
Jan 9, 2009, 7:41 AM
Post #5 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Last night at the shop I took off the catalytic convertor and put a piece of straight pipe in its place. Here in my state we don't have vehicle inspections. You could hardly see through the convertor so I thought maybe that was the problem. Nope. Still starts and runs good up to a quarter throttle when it bogs down.
Took the vacumn gauge and hooked it up to the intake manifold and it holds steady in the normal range on the gauge at 19-20 hg. At 2,000 rpm is raises slightly to 21 or 22 hg.
Fuel pressure was the same numbers I posted earlier. Fuel pressure gauge needle is still fluttering too. Hooked the gauge up on my friends dodge mini van and it holds steady doesn't flutter so the gauge isn't at fault.
Don't really know what direction to turn now.
I guess I should have spent the money and let a shop check and fix it. Hindsight...I know.
Any other suggestions? It's the only vehicle I have to drive.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 9, 2009, 7:59 AM
Post #6 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Ok The vacuum reading is probably ok just off by calibration but useful. It would be lower at 2,000 rpm with an exhaust restriction but really shouldn't ever be steady at 22Hg as that's a bit much. In fact with same test it should spike up there when a quick rev is done but not hold there normally. Air speed/the venturi effect can cause higher vacuum readings but I think you have the actual reading and the suspect item would have been the converter which you seem to have ruled out.
It does belong back in as it's part of the system and may be making improper adjustments with it missing - especially any post converter sensors.
I simply don't know what would be causing the fuel pressure fluctuations you mention and that probably is a source of the trouble,
T
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Loren Champlain Sr
Veteran
/ Moderator
Jan 9, 2009, 5:34 PM
Post #7 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Sam; Don't know why I didn't suggest this earlier. It's not a normal symptom, but have you looked at the MAP readings? What if..the MAP isn't seeing a drop in vacuum when under load? I doubt that a TPS would cause this type of symptom, either, but at this point, I'd check it.
Loren
SW Washington
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Sam77
Novice
Jan 9, 2009, 8:07 PM
Post #8 of 11
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Loren
I didn't think of that either. Will do some reading in the repair manual and see what I have to do to check it out or get the readings. Worth a shot. Will let you know what I come up with. Thank you
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Sam77
Novice
Jan 16, 2009, 7:07 AM
Post #9 of 11
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Re: 94 S-10 Blazer loss of acceleration
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I ended up taking my S-10 Blazer into a shop and have them fix it.
They found out that when the engine started to bog down that loud noises were coming from inside the fuel tank. They pulled the tank and along with a faulty fuel pump the inside of the tank was loaded with crap. All this combined to make my fuel pressure gauge needle flutter like wild. They told me when they had it hooked up to their machine that when they sprayed carb cleaner through the intake that the engine rpms increased and thats what led them to the gas tank and ultimately the fuel pump.
The pump was under warranty but I guess when the parts store asked about tank contamination the warranty went out the window. After a thorough tank cleaning and installation of a new pump and fuel filter its running like new.
I cleaned out the tank as best I could when I put the old (new) fuel pump in it but evidently I didn't do that good of a job. Only lasted a few months before the crap in there took out the pump.
Thought I would pass along what transpired to all of you. Thank you once again for all your advice.
Sam77
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Loren Champlain Sr
Veteran
/ Moderator
Jan 16, 2009, 4:10 PM
Post #10 of 11
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Re: 94 S-10 Blazer loss of acceleration
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Sam; Thanks so much for the reply. Let's keep our fingers crossed that the pump was the problem.  I did have a similar situation, many years ago. We finally, out of desperation, pulled the fuel tank and found newspaper wrapped around the pickup. Turned out that the guy had run out of gas and used a rolled up newspaper as a funnel. Drove us nuts trying to find the culprit, but that took care of the problem. Good luck.
Loren
SW Washington
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Sam77
Novice
Jan 16, 2009, 9:53 PM
Post #11 of 11
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Re: 94 S-10 Blazer loss of acceleration
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No problem Loren. There was alot of crud in the tank that evidently I didn't get out when I replaced the pump a few months ago but I didn't have much to work with like an auto shop does. She runs excellent!!!!
Took it for a 200 mile drive today and she never missed a beat. Way cool.
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