Hi all,

My '86 F150 4X4 has extremely bad hesitation problems under load. At idle, you can step on the gas no problem, but running, stepping on the pedal in any other manner other than very gently causes it to crap out. Feels like it's running out of gas.

Lots of hitching and chugging and very slow accelerating on the onramps. Using much too much gas and smells of gas once sitting. It does this hot or cold and has stalled because of it as well.

Throttle body and injectors were just cleaned. I'm about to replace the sending unit and in-tank fuel pump, hoping that this is where the problem is.

Any ideas?

Thanks.

Paul

 

Fuel pressure was tested (at the engine so I don't know if the problem is with the inline tank or the chassis mount) and read something like 33 lbs., which is low apparently.

 

Did you test the fuel pressure regulator? And what codes are coming up?
zanny

 

The truck was checked for codes and threw none. The fuel pressure regulator was apparently checked and seems okay. The fuel pressure (coming to the engine) measured at 36lbs (I had said 33 in the earlier post) which is supposed to be good.

The garages recommendation was to try the in-tank (primer) pump first. I can get it for about $65 CDN and seems like it's worth the risk.

I had also seen other similar posts mentioning the throttle positioning sensor, but the individual I spoke to didn't think that the symptoms were correct for that.

Thanks.

 

The tps can be faulty and not throw a code. It happened to me.
If you have a haynes manual, you can test it. You also need a digital multi-meter. The haynes manual can show you how to test the in tank fuel pump. Try a little testing before you throw money at it, and hoping it will get fixed. We all work too hard for our money.
And if you decide to replace the in tank pump. Do this, I unbolted my bed, and jacked it up , to gain access to the top of the gas tank. A lot easier than dropping the tank and unhooking all those lines.
zanny

 

Only problem with testing the fuel pump in the tank is that the condition does not exist under idle conditions. I can sit in P and rev no problem. It's only under load and acceleration that the problem exists.

I will try some of the tests outlined in the Haynes manual before proceeding. Thanks for the help!

 

I assume you have the 5.0 FI. My 86 is doing the same thing. I always have to shift early or it feels like I ran out of gas or I hit a rev limiter. Once I shift, it bucks once or twice in the next gear. I did all of the checks you did plus the TPS and timing advance. I still can't find the problem. Someone told me I should replace the EGR. I haven't done it yet so I can't say if that is the problem.

Basically I have no help for you...Sorry. If you find the solution to your problem, I'd sure like to know what you did.

Good luck!!
CR

 

Hi crothenberger,

Thanks. Yes, mine is the 5.0 L EFI but AOD, not standard.

Did you check your fuel pressure? I will certainly post if we figure things out. Funny thing is, this had gone on before and had "fixed itself" and is now back worse than ever.

p.

 

Have you guys checked your pip sensor?(profile ignition pickup)
This controls ignition advance.
zanny

 

For anyone still following this thread, this turned out to be a bad ground problem. Black wire from sending unit. Replaced about 5' of it and it solved the problem.

 

My truck has the same symptoms yours had. What sending unit are you referring to?

Thanks,
TM

 

The sending unit is on the top of the gas tank. There are two lines coming out for fuel and a plug-in connector to run the low-pressure in-line pump, control the sending unit, and read the float valve.

On my '86, the black wire from that plug leading back to the front of the vehicle along the frame was the problem wire. It didn't appear corroded from the outside so the best thing is to test it end to end or just to strip and replace.

Hope that helps.

Of course, there are still other problems with the truck...

 

other probs like what?

 

Other than the stuff I know needs fixing, like the rear differential for instance, it has the following symptoms:

- MAJOR pig on gas (and it wasn't always like that)
- grossly underpowered (much wheezing and stepping on the pedal but have trouble getting it up to highway speeds - not stuttering or hesitating, just generally underpowered)
- low oil pressure (not sure if this is related to above)
- more recently, getting high temperature, maybe because of the low oil pressure

Fuel pressure is good, plugs when changed were very clean, injectors check out, not throwing any codes. Timing might be off. It's a 5.0L V8 on an '86 F150 4WD AOD.

 

pdonis i had the same problem you were having with your 86 the hesitation. i changed both fuel pumps low and high pressure, fuel pressure regulator, egr, tps, and the filter after the high pressure pump, and still it ran like crap. so i was reading the old chilton manual and found a filter that i didnt even know it had. it is the one that is in the plastic canister half way down the truck in the framerail before the high pressure pump. so i pulled it out and sure enough it was full of dirt. so all i had to do was buy a $5 filter but i had spent about $200 dollars instead. makes me wish i would have bought the chilton manual a little earlier.