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Intermittent engine start trouble/help

 
Old 02-06-2019, 05:06 PM
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Default Intermittent engine start trouble/help

First, this is my first fun/project/ learning truck. my other is a 2015 F-150. I am mechanically inclined(union electrician) and I finally wanted to start to learn how to work on trucks.

Ill get to it. I bought a 1996 F150 5.0L automatic 2wD about a month ago. Has 117,000 original miles, was told the tranny had been rebuilt/replaced(not 100% sure which) at 80,000 miles. Had all new belts as well and what looked to be a relatively new installed Alternator.

Had zero issues first week driving the truck. Few days after that I had driven around town maybe 25 minutes, truck sat maybe for 15 min, came back out to start it up and it wouldnít start. Engine turned over each time I tried but wouldnít fire. I gave it a few minutes and tried again and it started.

Obviously I wanted to address the issue so I researched all I could and things to fix or change. As of now I have replaced Fuel Filter, ignition coil, spark plugs, spark plug wires, dist cap and rotor.

Even after this still having same issue. Ill
go into detail. I turn key to on, hear the fuel pump prime, turn key to fire, engine turns over and engine sounds almost like it has started, I let back the key and it sputters off. Sometimes it does this 3-4 times. Sometimes only once. I have never had it happen on a cold start ever. I also have never had the truck just shut off on my while driving, actually runs really strong.

All gauges check out, nothing running hot, battery is strong when off and while running.

Most recent troubleshooting I have tried was to run the truck off the second fuel tank, trying to determine if itís possibly a bad fuel pump and possible 2 bad fuel pumps.

Took it up to the store and same thing happened using this tank. Got the truck back home and swapped between the 2 tanks turning on and off. I definitely noticed it being much worse with tank 2, almost always not starting until I just held the key to keep turning over.

At at this point I def feel like this has to be a fuel injection issue, but again im new to this side of truck troubleshooting.

Thanks for taking the time to read this and any help is greatly appreciated.
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Old 02-06-2019, 09:06 PM
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All the truck's details need to be in your signature as this caption explains:


(phone app link)


Stop replacing parts. If you still have the originals, put them back on (except the filter & plugs) since there's apparently nothing wrong with them; they're almost certainly higher quality than any replacements. If you suspect a fuel delivery problem, the first step is to measure fuel pressure with a gauge, as this caption describes:


(phone app link)


If you have the old plugs, compare them to the inside back cover of the Haynes (which you should buy & read, after reading this caption):


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As an electrician, you should appreciate these captions:


(phone app link)


Even if it cranks strong, they can STILL cause every electrical problem, so take the time to read & inspect.
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Old 02-06-2019, 09:50 PM
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Common on these trucks for coolant or air temp sensor to go bad and not throw a code. They'll still function but send out readings that aren't accurate. Use your obd2 scanner and see if temps correlate with what's reasonable for the moment. The system might even have any old codes the po erased in memory.
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Old 02-18-2019, 09:48 PM
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I was able to test do a fuel pressure test today. With Key on engine off the guage peaked at 20 PSI for 1
second and slowly started dropping and eventually stopping at 1 PSI (took roughly 30 seconds to drop)

With key on Engine running PSI was at exactly 30 and held.

Based on the Haynes Manuel with KOEO I should be at 35-45 PSI and I believe it is supposed to hold there until I start the engine.

With that being said, should I be looking for a leak somewhere or do I have a fuel injection issue?

My gut is telling me is a fuel injector leaking which is why Iím having issues when the truck is warm. Is it better to just go ahead and change all 8 or just try and pinpoint the ones causing problems?

Last edited by Dunagan15; 02-19-2019 at 07:43 AM.
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Old 02-20-2019, 12:01 PM
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The pressure with the key OFF is irrelevant, despite both Ford & Haynes specifying it. If the pump can make & maintain running pressure with the key ON, the engine can run correctly.

Fuel injectors don't leak. Ignore your gut. Test the things I listed before.
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Old 02-26-2019, 11:55 AM
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Just wanted to give an update.

The truck is fixed. Issue ended up being that the distributor timing was off by 12 degrees.

Thanks all all for the help.
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Old 02-26-2019, 03:58 PM
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Well done! How did you diagnose the problem?
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Old 02-26-2019, 07:24 PM
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Originally Posted by drhayduke View Post
Well done! How did you diagnose the problem?
well not long after I posted this. I had same issue happen. After thinking it was fixed for a few days it once again reared itís ugly head.

Im sure the distributor timing will help the overall performance of the vehicle but back to diving back into this bitch of an issue.
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Old 02-26-2019, 08:47 PM
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You are at the very bottom of what is considered normal fuel pressure for your engine. The pressure should also hold for a much longer period of time after shutdown. You need to do some diagnostic work to see if a fuel injector is drippy or the check valve in the fuel pump has issues. I would also pull the vacuum line off your fuel pressure regulator, if there is raw fuel present, change then regulator.
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Old 02-26-2019, 09:07 PM
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Originally Posted by raski View Post
You are at the very bottom of what is considered normal fuel pressure for your engine. The pressure should also hold for a much longer period of time after shutdown. You need to do some diagnostic work to see if a fuel injector is drippy or the check valve in the fuel pump has issues. I would also pull the vacuum line off your fuel pressure regulator, if there is raw fuel present, change then regulator.
I checked the regulator already. Blew out that line and tested with and without. No change. I also thought a fuel injector may the the problem but have not had the time to try and get the rail out to check them or replace them 1 by 1.

As far as the fuel pump goes, is there any way to know what the fuel pressure was from the factory? Other than the 30-45 psi window? I agree that 30 psi is also on that borderline but the fact that it held steady made me think the fuel pump was not the issue, but I could be wrong.
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