wiz

Hi everyone. This is my first post, so my apologies if I'm posting in the wrong place. Also, I have searched for days and cannot find an answer.

Here is the situation: 1998 F150 4.6L ran great at first. The fuel got low and the truck started sputtering. So, I changed the fuel filter. Truck ran great for 10 miles... started sputtering again. Changed fuel filter again. Same thing.

Then my step-son wanted a car towed... reluctantly I agreed (since truck was running like crap). Well, while towing the car the truck got real bad and blew a hole right through the passenger's side rear catalytic converter... and caught my floorboard on fire.

So, I figured hey a bad 02 sensor or maybe the cats were plugged. So, I've gone and put completely new exhaust manifolds, new cats on both sides and new 02 sensors as well as a new egr tube. It's all brand new.... but, the same thing happens. If I pull the negative terminal for about 10 minutes and start the truck it purrs like a kitten, then progressively gets worse until it's running like complete crap. I have no check engine light on, so I'm assuming no codes (although I have no way to check atm).

If anyone has an ideas or can point me in the right direction I'd really appreciate it. I've got a ton of time and $ in this project and still no truck

Carcrazygts2

Bad pcm. The early F150's have a issue where the solder joints on the eprom crack and pull away from the circuit as it heats up. You may also have water in your fuel.

wiz

Thanks! I will get a new pcm and then post back here.

Carcrazygts2

before you drop the coin on a new pcm and having it programed by the dealer take it to ford and let them diag it for about $100.

iowaredneck

^this

wiz

Alright, thanks guys. I'll take it to a dealer and see what they say.

akdoggie

Since it's hot related as to when it starts running bad, EGR system probably is clogged or damaged somehow. This will cause the bad cats also. I tend to think it is in that particular area. You say you replaced the EGR tube, but how about the valve itself?

wiz

Well, I don't actually think it is heat related... in fact, I'm sure it's not.

If I disconnect the negative battery terminal and leave the truck for 10 minutes and then start it, it runs beautiful. Within a minute however it's running rough again, sputtering even when I give it gas.

EDIT: I should note that if I don't disconnect the terminal and let the truck cool, it still runs rough immediately upon starting. It's only when I reset the electronics that it runs great for a moment.

I did not replace the egr valve, only the tube. I replace the tube because it connects to the manifold and that connection was rusty, so I figured go ahead and replace it now.

I have the truck scheduled to go in on Thursday, but I was hoping to figure this out myself... after all this work replacing the exhaust manifolds and catalytic converters, I'd hate to pay a garage now lol... but I've got to get this thing running right, and it has to be something small... I think egr valve is a candidate.

Frank_Ford

I agree with that Alaska guy on the EGR. This may be stuck and causing your problem.

While the engine is running, disconnect and then connect the vacuum line to the EGR and feel if the diaphragm is moving. If it doesn't move, you either have a stuck EGR or , less likely, a bad diaphragm.

You can take the EGR off and clean the inside with a wire brush to get it back to where is operates freely. Ford does not recommend using chemicals on the valve because they can damage the diaphragm.

Carcrazygts2

It could be a faulty DPFE. It controls when the EGR should open, but if the EGR is opening at idle and not in gear there are other issues. Becuase according to the ford manuals EGR should not be functioning at idle.