1994 F-250 HD, 4X4 Off Road, 5.8L 351 EFI, 5 speed ZF transmission.
I have been working this issue now for about six months when I can get the time and it is kicking my a##. It all started when I got off of a six month deployment and went to drive it. It seamed to run just fine, but when I would go to get on the accelerator, it would bog down like it was either missing, not getting fuel or not getting spark.
I have no check engine light and the only code I ever pull is a constant memory code for EGR voltage high. I can't remember the 3 digit number, I'll get it later if it's important, but I think its just a symptom of the loss of power. I've tested the EGR valve and the switch that sits on top of it and it all checks out.

What I have done and found along the way. I could find nothing wrong at first. I did a tune up, plugs, wires, cap and rotor. I also changed out the fuel filter. I had some suggestions that it could be a fuel pump, but I have two tanks and from what I have gathered in my research is that each tank has it's own pump. And two pumps going out at the same time is not likely. Maybe I'm wrong. I've searched all through and around the engine for any type of vacuum leaks or broken wires all vacuum is good and I can't see any broken wires. Truck, runs but, not well. If I accelerate slowly it seams to do okay, but if I get on it, it bogs down and knocks. It does okay on flat level road at any speed if I don't accelerate quickly, but if I come up to a hill, it will lose power and knock.

So, I took it to a garage to see if they could find problem. Well, they replaced the fuel pressure regulator because it was putting what they said was high pressure, into the fuel rails, 70psi, should be around 35psi and they also sent in the computer to Ford to have it re-flashed. This did not fix the problem... Don't think I will be going back to that garage for service or help.

Next I contacted a friend of mine who is ASE certified to see if he could give me any tips. Because it had sat for over six months, he recommended taking the fuel injectors out cleaning them, repacking them (seals) and putting them back on. When I took off the upper intake manifold I found that a rat had used my passenger side injector wiring harness to sharpen its teeth. Specifically cylinders 2 and 3. Problem solved right!!!

No...

I repaired the wires, put it all back together and still the same issue.

Since, then I have troubleshot and found really nothing that I can point to with certainty. I shot from the hip and replaced the TFI module, because it almost seems like a timing issue. My thoughts of it being a timing issue is because it's like the electronic advance isn't working right. But, it has similar but not the same problems with the SpOut plug out when the electronic advance is out of the picture. My next part to throw at it is a distributor, but I'm having a hard time believing that would be it. Many friends I have talked to make all types of suggestions. MAP sensor, TPS, Vacuum, fuel, spark, etc. I don't have any codes. It all works, when I give it nice easy throttle. I only have issues when I get on it.

I have opened it up quite a bit. I have a BBK oversized throttle body, with a spacer, shorty headers and a three inch cat back exhaust along with a high flow cat.
Is it possible that I've opened it up too much for the computer to be able to keep up with the demand?

I'm looking for some help from this community. I have spent months looking through this forum for similar issues, as well as other forums. I've done everything I can think of outside of individually reading out wires one by one.

If there is anyone out there who could shed some light on this problem I would be grateful.

I MISS MY TRUCK!!!

 

What is timing set at?

What does timing go to when you plug the SPOUT jumper in?

Does it bog down while in park or neutral?

What is Fuel psi while running? With vacuum hose disconnected? What does fuel psi do when you blip the throttle?

Have you pulled the PCM and checked for failing capacitors?

 

If it starts knocking when you try to accelerate, then it's not the timing. It's getting lean, so you have a fuel delivery problem, is my diagnosis from what you have stated.

 

So what is the fuel pressure at idle with and without vacuum on the regulator?

 

Not quire sure what the shop you went to did with the computer as my understanding is that there's nothing to reprogram or re flash in them.

 

Agree - I think they just charged him an extra hour of labor for nothing.

 

I'm thinking the same thing. That's why I'm curious when he can pull the PCM and inspect it.

Hopefully he'll post back soon....

 

Yes, sorry for the delayed response. I work about 100 miles away from where I live and the truck is located and don't always have access to a computer.

Timing is set to about 12* btdc. When the spout is in timing appears to advance correctly. Not sure exactly what it is I will check next time I get a chance.

The engine does bog down when in neutral when you blip the throttle (accelerate quickly) If you ease into the throttle it seams to do okay but, you can tell its still starving and slow to catch up. The same happens when driving, put the throttle to the floor and it will bog down and knock, ease into it and it goes but, it still isn't right.

I do not know what the fuel pressure is. I was told by the mechanic that the regulator was reading high at 70psi and that is why they replaced it and that the new regulator is reading 35psi. I have not checked it myself in the book I have to see if that is correct. I don't know if I have the correct tools. Any help and advice as to how to do this would be appreciated.

I have not checked the PCM capacitors. I do not know how or even where to begin doing that. All I know is that the shop sent it in to Ford to have it re-flashed. Mechanic said that after they did the wire checks that re-flashing the PCM was the next step. I would think that that would have been part of the process if they had it re-flashed. On a side note, I have sworn off that shop. I'm not too happy with the fact that they charged me money and didn't fix the problem. But, that is another long story.

Vacuum when the truck is running is good. What that number is, I don't know, I will check when I get a chance. The system is tight.

Thank you for your help!

 

Ditch the TB spacer(it does nothing) and put the stock throttlebody back on, your problem may be related to the TPS sensor and this will be an easy way to test that... assuming the BBK came with it's own sensor.
Did you install an O2 sensor in the new exhaust? If so where is it located?

 

Problem solved!

It ended up being the distributor.

I did all the suggested above as well as threw some parts at it. MAP sensor and TPS. I also had the computer bench tested and it checked good.

The last possible part it could be was the distributor. After finally getting the correct one with the right steel timing gear, (1994 and newer 351W have steel cam gear) problem has been solved.

Thank you!