Engine Misfire

[Stinkers]

Hi Everyone,
Ok, here is my latest problem. My truck stumbles and seems to be misfiring at highway speeds between 55-70 mph when accelerating in overdrive. As soon as it downshifts it is smooth, but under load in overdrive it misfires. I have run cylinder contribution and injector buzz tests and the truck passed both. It is not showing any codes either. I recently replaced the HPOP and IPR valve thinking they might be the problem but no luck. Fuel filter is new and clean. I am only making about 17 psi boost with my TS chip cranked up and the peddle on the floor in third gear near redline. I am completely stumped. Any help would be much appreciated. Thanks!

[Stinkers]

Well, I figured out my problem and thought I'd let everyone know just incase someone else is having similar problems. I had cleaned out the little screen on the fuel pressure regulator a couple of months ago so I didn't think to check it again until last night and it was clogged up again. I took the regulator completely apart and cleaned it out. The truck is running perfectly again and is easily boosting over 20 psi.

[ktfjammer]

Originally Posted by Stinkers

Well, I figured out my problem and thought I'd let everyone know just incase someone else is having similar problems. I had cleaned out the little screen on the fuel pressure regulator a couple of months ago so I didn't think to check it again until last night and it was clogged up again. I took the regulator completely apart and cleaned it out. The truck is running perfectly again and is easily boosting over 20 psi.

Where is the fuel pressure regulator? Is it a big job to take it completely out and clean it out? Thank you, Jim

[Stinkers]

The fuel pressure regulator is bolted to the side of the fuel filter housing on top of the engine on 1994-1997 trucks. It is realitively easy to disassemble and requires removing two bolts, some hose clamps and a circlip. The 99-01 7.3 liter powerstrokes (it looks like yours is a 99) have a slightly different fuel pressure regulator setup. It is still located on the side of the filter housing but if I remember correctly, is somewhat simpler and is integrated into the housing. There is not much to take appart except removing the spring and plunger via two small bolts (the same way one would do if doing the fpr shim mod). I should tell you that my problem in the end was primarily due to bad injectors. The injectors passed buzz and contribution tests, but failed to perform under driving conditions, so they were hard to diagnose. If your truck is misfiring and has around 200k on it, injectors could be an issue and should be considered. I upgraded to stage 1's by Jim Rose at Rosewood Diesel and it has been the best modification I have done. Good luck, I hope this helps.

[SRT-Diesel]

Same problem with a 6.0.
Took my tune off and now its fine?

[Stinkers]

It is entirely possible it's just bad tuning....that's the first thing I would look into, unless the truck has run fine with the tunes previously. If it has run fine on them before, it could potentially be an injection issue.