I have a 1991 f150 with a 302 in it. The truck had been sitting for 5? years or so, and just recently a buddy of mine decided he wanted the truck.

So I pulled the truck into my shop, I removed the injectors and cleaned each one. (I followed the manual injector cleaning process)

I bought new plus and gapped them to .50.

I put a new cap and rotor, and plug wires, and I routed them correctly, using the plastic spacers for the wires.

I timed the truck to 10 degrees before top dead center.(removed the spout connector to time it)

I cleaned the fuel tank, and threw a new fuel filter on the truck. I dont know what the fuel pressure is off hand, but the truck is running and driving well, minus this.
Fuel pressure regulator tests out good.

I cleaned and tested the tps and iac valve (swapped to a truck I have) and it was working good.

New air filter, and oil change was done as well.

No codes show at all using the "paper clip" method of testing.

The issue is, while youre trying to get up to speed, there is a hesitation. If ya hold the pedal in that certain spot, its like the truck wants to die out, completely. I havent actually held it in that spot for it to die out though.

So im thinking I have most of my regular tune up bases covered, but by the life of me, i cannot figure out why the hell it wants to die out like that.

The truck runs really good other than that, starts good, idles good, drives good (minus the leaky front tranny seal!)

Any advice or something to look at would be greatly appreciated.

 

I'm having a very similar issue with my 460. Interested if you hear anything. Is it only under load (like with the A/C on) or all the time?

 

Currently the ac is off, unplugged. Just that one point in acceleration, and thats it, the truck runs superb otherwise!

 

Could you clarify that statement above?

"No Codes" means no codes in book which indicates your test procedure is invalid. At the very least you should have gotten the System Pass code of 11 for KOEO/CM/KOER. Anything less means you have more troubleshooting to perform.

 

No problem codes.

 

So that means you did get the System Pass code of 11?

 

Yes i got the system pass code. I tried the method of testing on my other f150 as well, with the same results. (just to make sure I was doing everything correctly, and my other f150 doesnt have any issues)

In short, the truck is telling me that its ok. No problem codes.

 

So many times someone posts "I did not get any codes" which they think is a good thing. Sorry to keep asking the same question but I was looking for "yes, I got the System pass Code".

Back to your original problem......how did you test the TPS? Only at closed and wide open throttle? Did you slowly open the throttle to verify the TPS output is linear with no dips in the reading?

 

Since the truck probably was without battery, maybe it just needs to re-learn, as in having the engine running for a while, see if it smooths off. Check for any broken vacuum lines, and if all these check, try using some Seafoam. Other than that, maybe a loose ground could be causing problems, but that's a long shot.

Maybe the engine just needs to be run for a while, when it's been so long it usually is just that.

It sounds like you were very through, but I do hope you replaced the oil and the coolant, it shouldn't cause your problems, but it's always good advice

 

I will add one other option. I agree check the tps. But also it could be that the egr valve is gummed up or bad as well.

Maybe also an o2 sensor? First I'd go for the egr though

 

No worries rla2005, it pays to have me relay as correct info as I can!

For the tps, i swapped it to and from another truck I have, that has no issues. Nothing changed on either truck. My "good" truck ran good with both, and the "bad" truck still had the hesitation with both tps. It was actually my first thought to change that (after the injectors and tune up), but it made zero difference. I didnt test it with a meter though, as I had assumed that the swap should be a sufficient test. Thoughts?

I DIDNT do anything with the EGR yet, or the o2 sensor. I had figured the o2 sensor would throw a code, and I figured that if the truck ran good before it sat with no issues (and it did run good!) the egr wouldnt just plug itself up by sitting there. Thoughts?

I did give it an oil change yes, but I didnt change the coolant! I did check it out though with a test kit, and it checked out good, so I left it alone.
And I did try and think of everything it could be, test it, swap it, or fix it or whatever so I wouldnt have an issue.

My buddy drove the truck for two hours back to where he is from then blew out the famous front tranny seal, so it looks like we will have to fix that before doing much more driving for the computer to relearn. I will try that as well though, but will try other stuff that I can do in the meantime if anyone has more thoughts and ideas!

Ive ran into weird issues before, but this one does have me a little stumped.

 

She sounds like she's going lean or we've got some weakness in the ignition path.................with the truck sitting so long, have you run all possible vac leaks to ground?

I'd also get a reading on fuel pressure ............essential stuff........

 

Sorry I havent checked this out for awhile.

I have checked for vacuum leaks, and there isnt any. I havent got an actual fuel pressure reading number, but I think I can rule it out, as Im sure if there was a fuel pressure problem, it would present itself over various stages of throttle useage, not just one part.

Am I wrong in thinking that?

My buddy has the truck at his place 3 hours away now, with little tools, so I might have to take an inventory of things to try, and try them next time I go to his house.

 

Fuel pressure should be around 33-35psi at idle.............40-45psi (underload/WOT) --- disconnect vac line at regulator to get "underload"....