I am new to this forum, but not car forums in general. I was hoping someone ran into a similar prob as the one I am having.
I am working on a 1986 F-150 5.0, and it has not been running for about two years. The truck was running badly when parked for the final time, I wasn't there to see why. What I have been told is that it was running real rough and shaking.

In my inspection I see that one cylinder (drivers side nearest the firewall - sorry I do not know firing order) is constantly receiving gas and is filling up the cylinder, only when the key is in the "on" or "start" position. When in the "off" position, the gas is shut off.

The problem is that the bore fills with gas, and when that piston is on the upstroke, the engine struggles to raise that piston because of compressing an entire cylinder full of gas. The gas will squirt past the piston rings and fill the crankcase with gas. On the downstroke the piston moves freely while cranking, but again struggles on the upstroke because it quickly fills with gas AGAIN. Also, when I remove that spark plug, gas shoots out of the plug hole about five feet in the air and outside the engine compartment. The engine turns freely on the up and down strokes when the plug is removed due to the relief of pressure.
So the engine turns over, but will not fire
(if it fired, it maybe would explode).
Also, there is gas in the crankcase due to this.

I bought a new fuel injector and replaced it, thinking the injector was stuck in a constant "open" position, always allowing in gas. Not the case, prob still exists. I also thought a fuel press regulator was failing, but now I doubt it. (haven't tried that)

I am led to believe that the fuel injector wiring is bad, possibly grounding out and is stuck "open". Can anyone confirm this?
Otherwise my guess is that the truck's computer is faulty and is telling the injector to stay open. What do you guys think? Anyone else experience this? Any help would be appreciated.

 

Oh, BTW, I plan on testing the bad fuel injector wire theory by taking a 12V test ligt and measuring the the juice going to the injector.
If I am right (the wire or computer is bad) then the light testor should stay lit constantly, correct? If all was working well, the the light should pulse for every burst of gas, right? Please help me out.
Question: does the injector get 12 volts power from the ECM? Or is it less juice? If less, it may not light my 12V testor at all....

If it turns out to be a bad computer, how can I verify this? Please tell me how to dignose it. And remember, the truck has been sitting dead for a couple of years, so the trouble codes will show up as 19 (batery power). I wish I was able to fix the prob while the truck was still running....

 

I answered on the 302 forum also - fuel pressure regulator is bad - you have all the classic symptoms. It mounts above the #8 cylinder - easy fix. I also have an 86 F150 302 EFI in a 4X4.

 

My problems were a little different on my 85 but after replacing the fuel pressure regulator, it ran beautifuly. passed emissions finaly as well thanks to that fix.

good luck.

 

Great! Sounds like an easy fix.
I am fixing (attempting) the truck for my aunt. If I get it going I will try to offer her some cash and buy it from her. Then I will probably be spending more time here with you good folks.

Thanks for the help. I appreciate it.

 

Just to follow up, the regulator was the problem.
Replaced it and the truck came alive after 3 years. Puffed all kinds of white smoke, but cleared up and now purrs away.
Thanks for all the help.
smilie('')
https://www.ford-trucks.com/dcforum/Images/wink.gif

 

Amazing how one item can make such a big difference, huh?! Glad to know you got it running.

 

Hey there, glad to hear that helped. I ALSO went through all that frustation. One shop charged me $800 worth of stuff from MAP sensor to you name it. Never fixed the problem! (oh well, least I got some new parts) These guys even went as far to say my TRANNY was causing the problem !! Well ,I finaly found a shop owner out here who drives and owns Ford trucks, walked into his shop and before I could open my mouth he said "fuel pressure reg.". Unbelievable!

BTW- ASAP run some 'BG 44K' fuel add. through that system (maybe twice)and you'll be amazed. best stuff I've ever used. $18 to $20 at NAPA or Car Quest.

Chris

 

...shoulda offered the cash before fixing it...Now she'll NEVER sell it!! Nice to hear it runs.