I posted this in the 80-6 section, and I would like to post the question here also in case some of you don't visit that other section.

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....

 

The injectors have a constant 12v power supply.The pcm completes the circuit by applying ground.So if that injector wire is going to ground it will fire.Now Those models if I'm not mistaken bank fire the injectors,that is it fires all 4 on one side at the same time.Check the ground wire from the injector to where it ties in to the others.If the wire to the pcm was bad all 4 injectors would be firing.Also check for spark at that cylinder.

Billy

 

Sounds like a fuel pressure regulator - mounts right above the #8 spark plug (drivers side rearmost plug) One exciting way to check is remove that spark plug and have someone hit the starter - you will have an immediate gusher of gas shoot out the plug hole. When it goes bad it tries to pump the gas for all 8 cylinders thru the #8 injector.

I have an 86 F150 302 EFI and about a year ago I went thru this very process. Fuel Pressure Regulator fixed it - good luck!

 

Some more thoughts.First thing I would do is change the spark plug and hook up a timing light to that cylinder while cranking see if it's firing.It probaly wont for long if it is running that rich.If you have enough slack in the leads,swap the injector wires.That will tell you if it's in the wiring for that cylinder.Next due a compression test on that cylinder.The number 8 is notorious for problems.

Billy

 

mtflat:
That sounds exactly like my problem, what you described. That is great. The fuel whooshes right out the plug hole when hitting the starter with the plug out.
So just replacing the regulator fixed it all for you? Hopefully so....should be an easy fix.

Cajunbronco:
Thanks for the advice. All the info and tips you supplied will be my second course of action if the regulator is not the only prob. I am expecting more problems possibly, hopefully rings will be ok. A compression test may be a good idea to check.

 

Yes, the new regulator fixed it all. About a half hour driveway repair start to finish. Go buy a new one and it'll be self-evident where/how it installs.

You might want to squirt a little motor oil in the plug hole on #8 since it is pretty well washed out, and let it leak down for a while - also be sure to change your contaminated oil before you turn it over.

My youngest son was driving my 86 when it started acting up and he kept driving until it wouldn't run. Engine had about 160K at that time so I just did what I suggested above. No apparent harm to engine resulted from the whole ordeal.

 

I concur! Fuel pressure regulator!

 

Thanks guys. I'll tackle the job this weekend probably. I will reply back then and let you know how it goes.

I have a few other things to do to it to get it back on its feet, I knw a brake line is busted and probably has sucked in a bunch of air, so it will need a bleed. It has been dead for a long time, so it will need a full tune, as well as who knows what.
Thanks again.

 

mtflat:

I got to thinking about all the steps I need to take to make the repairs before finally try to crank it up, and I was wondering how I will get all the gas out of the crankcase----not all of the gas will drain out, right?
Did you get gas in your crankcase when your regulator failed?
How did you get all the gas out?

Maybe put an air compressor hose in the spark plug hole and blow the gas out the drain plug?
I really would like to avoid dropping the oil pan if I can help it.
Any ideas? Or am I too paranoid about getting the all the gas out?

 

You could "purge" the engine by draining the oil leave the drain plug out and introduce air thru the oil filler nozzle and let it blow for a while. Make sure you do not have any open flame or sources of ignition. That should evaporate any fuel in the pan. You could also reverse it and blow from the drain up into the engine, leave the oil fill open and pull the pvc valve. Then fill it with oil, run it a few miles, drain and re-fil you should be good to go

Hope this helps
Good Luck with your project

Gasman
Do you have Gas?
Propane Execeptional Energy

 

Good idea, I should have thought of that. Thanks.
Guess it's just a symptom of being Monday.

 

I did have gas in the oil just like your truck. You and gasman talked it out tho. I just changed oil a couple of times, figured that the pcv system would also help to remove residual gas.

 

You guys hit the nail on the head. Fuel Pressure regulator.
I want to say thanks to all that helped, the truck is rolling once again after a 3 year hibernation.
It even purrs like a kitten, pretty unbelievable how well it is running after sitting outside for three years dead.
smilie('')
https://www.ford-trucks.com/dcforum/Images/fte1.gif
Once again, thanks for your help.

 

On my way home last Friday my 1988 f150 just shut off and would not restart. I also noticed a very strong gas smell. The engine would try to turn over a few times and would then just stop.I'm keeping my fingers crossed that this is the same problem that you have just fixed. I just recently bought this truck and just a tad bit upset that it crapped out on me already.

Mark