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1975 Ford F-100 Won't Start
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Grif
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Nov 25, 2008, 7:13 AM
Post #1 of 9
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1975 Ford F-100 Won't Start
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Howdy folks,
I have a 1975 Ford F-100 pickup that won't start. I think I've got it narrowed down to a lack of spark because I smell fuel when I turn the starter. Also, I tested for a spark with a plug tester light and the results were a little strange. With the starter cranking, the test light lit on cylinders 1 & 2 (driver's side of engine) but no light on cylinders 5 & 6 (passenger side). It's a V8 and I didn't test the other 4 plugs for spark. I bought this truck last summer and the cap and rotor appear to be new and in excellent shape. I replaced the ignition control module because I had an extra one sitting around but that didn't help. Any ideas?
Thanks for your help!
Nick
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dmac0923
Enthusiast
Nov 25, 2008, 8:11 AM
Post #2 of 9
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Re: 1975 Ford F-100 Won't Start
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one thing you didnt mention......was it running once before? or it never ran and you just now got around to trying to fix it?
first thought would be corroded terminals on the cap & rotor. take some sand paper and brighten them up.
is the wires firing order is correct?
__________________________________________________
2015 Jeep Grand Cherokee
2002 Ford Ranger
2004 Toyota Corolla
1969 Ford Mustang Mach 1
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 25, 2008, 8:18 AM
Post #3 of 9
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Re: 1975 Ford F-100 Won't Start
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Hmmm? If there's ANY with spark it should be able to "distribute" it. It's out there - but does rotor turn when cranking? Dist shaft might not turn - worth looking.
Clean up as suggested and also a genle "blow out" with air inside distributor might get some cobwebs out of there also,
T
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Grif
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Nov 25, 2008, 8:45 AM
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Re: 1975 Ford F-100 Won't Start
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Thanks for the quick replies, guys. I should have mentioned that the truck started and ran fine, I stopped to get gas, and it wouldn't re-start.
I didn't pull out any of the plugs, just connected the tester in series between the plug and plug wire coming from the distributor. I've never used the tester before so I'm not sure how bright it should be. On the 2 plugs I tested with a spark, I got a flashing light which wasn't particularly bright.
Sounds like my coil isn't necessarily bad since the test light indicated a spark on at least 2 cylinders. I'm going to hook the tester to another vehicle to see how bright the light gets. It seemed dim to me on the truck but maybe that's as bright as it gets.
I haven't checked to see if the rotor is turning when cranking...I'll check tonight.
I don't think the carb is flooding...How do I know this other than seeing puddles of gas around it?
Thanks for your help, everybody!
(This post was edited by Grif on Nov 25, 2008, 8:50 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 25, 2008, 9:18 AM
Post #5 of 9
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Re: 1975 Ford F-100 Won't Start
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What engine does this have?
Trouble spot for the vintage was carb and choke issues. Make sure it can open and shut while holding throttle up a little just with engine off. You can even see squirts of fuel from accellerator pumps in these.
You saw some spark so if distributor is turning I don't want to badger that with the history of just getting gas and it quit.
Fuel filters were small back then and fuel pumps are rubber parts that can fail easily too. Check everything at the age but think about adding a fuel filter after pump in line to carb that you can see thru. Take line off fuel pump and put a peice of line into a container and see how much it can pump. Fuel pressure is low on these - 4-6 psi or so. If it fills a small can fairly quickly that's good - then look at the fuel to see what it looks like too for junk or whatever.
If lacking fuel it should start for a moment with starting fluid. If not look at a couple easy plugs for being soaked with gas.
Lot's of possibilities so let's get some history on it. Miles if known, if timing chain has been done or don't know. Does automatic choke still work properly.
Spark plug note: This and newer stuff too, plugs that get gas fouled from attempts to start can get wet such that only heat from either running or heating them up will allow them to work again. Air dry doesn't always work at all. The more failed attempts to start it the more the plugs will become an issue even if you fixed or found the trouble. If new plugs are in order quality counts. If they were flooded, leave them out (mark wire locations!) for a good long time helps too.
Hit back - we'll get this going soon,
T
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Grif
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Nov 25, 2008, 9:38 AM
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Re: 1975 Ford F-100 Won't Start
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Thanks for your help, Tom. Here are the details:
The truck has a Ford 390 engine in it. The previous owner told me the original 360 blew up and it was replaced within the last couple years with a 390 out of another old Ford (it has not been rebuilt, and he told me it had "60-80 thousand miles on it"). The first thing I did at the gas station when it wouldn't start was spray a couple squirts of starter fluid into the carb. It still wouldn't start (not even momentarily) so I figured it was a spark issue. My spark plug light tester seems to indicate it is an electrical problem since I'm getting a spark on some cylinders but not all. I don't know if the timing chain has been replaced recently. It has a manual choke and I assume it is working properly, but perhaps I should check that. I haven't pulled any plugs but it sounds like I should do that. I was hoping this would be a simple thing like switching out my coil or ignition module, but probably not. What do you suggest I try first? Thank you!
Nick
(This post was edited by Grif on Nov 25, 2008, 9:40 AM)
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Tom Greenleaf
Ultimate Carjunky
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Nov 25, 2008, 10:04 AM
Post #7 of 9
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Re: 1975 Ford F-100 Won't Start
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Ok: Agreed this is a spark issue. Now I don't know quite what the set up is for the distributor and the module - a huge box they used to put on fender area underhood - those should show either blue or yellow connector plastic and I don't think they interchange?? Been a while you know!
There were no manual chokes in Fords of the vintage so it's been butchered with some contraption that isn't the up front issue but too bad because it will cause more problems than it solved to do that. They can be fixed to work at intended if you give it some time - so big deal.
Timning chains frequently used nylon on cam gears. Miles or not with age they crack and chunks come out! This would show up as a funny sounding engine when cranking and low intake manifold vacuum at first. They usually will still spin such that rotor in dist will turn. The shaft on some Ford distribs used a lower gear with roll pin that can shear! If so, rotor under cap might just spin around by hand or not turn with cranking. Again - engine might sound funny when cranking and perhaps select just a couple plugs to show fire on! Ah ha!
The module thing: If you have one you knew worked put it back on if for only a test. Check out the heavily greased plug in for that, that it looks good.
Real coil failures are rare and more apt to have a crack (carbon trace) at the tower and fail that way. You would probably see stray sparks there when dark or could stall the engine just spraying it with water but it's already dead so don't do that now.
Try pulling a plug or two and check for spark with the plug out and grounded. Not sure what you are observing with your tester. Thru all the many years I've never found WEAK spark but rather good, none or erratic.
What stinks is wondering about whether plugs are actually firing if they've been wet. I have a couple of K-D tool -- "Portable Ignition Systems" that just have a coil wire and when hooked up sprays spark so hard it blasts thru wet problems and fouled plugs right away and dries them out with a stumbling but running engine and can't find those now new or used and sure are handy as with any ignition failure you can still drive a V8 to get home as long as rotor turns close in distributor. Cool tool!
Keep checking and report what you find. I'm here and perhaps others watching,
T
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Grif
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Nov 25, 2008, 10:42 AM
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Re: 1975 Ford F-100 Won't Start
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OK, sounds like I need to make sure the rotor is spinning like it should. If that's OK, I'll check the plugs. I'm going to forget the light up tester and see if I get a spark by holding the spark plug wire near something metal. I'll let you know what I find out. Thanks!
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Grif
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Dec 2, 2008, 10:29 AM
Post #9 of 9
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Re: 1975 Ford F-100 Won't Start
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Hey everybody,
I got the truck running. Turns out it was a bad coil. Thanks for your help!
Grif
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