Engine/Transmission (1998.5 - 2002) missing/misfiring with comp on

[DLausche]

It reminds me of an old Bronco I used to have that was misfiring. It is only noticeable at highway speeds (70+) and only with the comp on and heavy on the go pedal. Had it on 3x4 yesterday and when I give it more juice after the wastegate is opened (~30psi) is starts to buck/miss a little bit - and lots of smoke. My thought is this is a sign of too much fuel. But, what is the phenomenon that causes the feeling that is it misfiring? How much higher can I run the boost on a stock headgasket?



Oh, yea, brand new VP and brand new DD3 Jammers just a few weeks ago. Just redid the pump wire connection yesterday to make sure I didn't have a bad connection or something.



Thanks

-Deon

 

[DavidC]

What is your fuel pressure?. New fuel filter installed?. Others have moved the ground to the battery that has solved problems. I had to exchange a DDUFM a few years ago for a slight missing problem and setting a code, 253 if I remember right (timing issue). If everything appears to be ok remove the comp. and restore system back to stock. If that resolves the issue I would think it is time to think about an exchange. If you need to exchange they want everything including the wiring harness.



Dave

 

[Wyatt 1]

what was your rpm's like?

 

[DLausche]

Fuel pressure about 7 when it was missing and about 1800RPM at 70Mph. Filter is not new, but not too old. I don't think it is fuel pres related because I just went for a test drive and with the comp off and the pedal all the way down it pulled strong, no missing sensation, and fuel pressure was even lower at 5psi. I'm thinking it has to be comp related. But, the VP and DD3's are the new part of the equation, not the comp. Yea, I know 5psi is not the best. I'm hoping to get my new pusher pump on today to get the FP back up a bit.



I moved the ground wire that is in the wire loom with the comp pump wire directly to one of the bolts on the top cover of the pump yesterday. That and a fresh connection on the wire to the pump did not make any difference.



I'm thinking now that I will go over all of the connections to the comp and unplug/replug them together to see if I have one that is loose or something. After that maybe borrow a buddies comp and see if that makes a difference.



-Deon

 

[Wyatt 1]

I hooked my ground for the comp up directly to the battery. They say that at 50 psi you are pushing it, I dont have experience to say how true that is, but there are alot of people here who have probably pushed those limits and can tell you from experience check out the PDR website under products they explain alot of thins, also http://www.3d.otisnet.net/ it is a good website to visit if you have questions about your truck, it has helped me out, if you know all of this already, then I will just shut up,

Henry

 

[KMahnke]

Just curious, did you ever find out what the problem was? My '01 just started doing exactly what you described tonight when I was driving home. Feels like a misfire when it starts building boost (around 35 - 40 psi). Doesn't do it when comp is off... and theres not a big difference in power between 5x5 and off, besides smoke ... I noticed it hasnt felt like its been giving 100% for the past couple weeks ... . especially when i had a chevy 4500 DMax almost whoop me ..... Checked for codes and it didn't throw any and I'm gonna check the wire tap connection tomorrow, I used the scotch lock and I'm thinking ( and hoping) its just coming loose.

 

[DLausche]

No, I never did figure out how to fix it. With the Smarty I have now I never turn the Comp on anymore so it's not a big deal. I did get several ideas for fixing this though. As best I can recollect, the ideas were resetting the APPS, making sure of a good ground on the Comp, add some sort of noise filter (DTT?). The most logical thing I had heard was that the signal from my APPS was a bit noisy. This is not noticeable until I had the larger injectors and Comp together which caused the noisy signal to be amplified to a point that it was not only noticeable, but really annoying.



Somthing doesn't sound right of you don't notice power diff between 5x5 and off. Try using a posi-tap connector and nolox when you take off the scotch lock tap. IMO, the posi-tap is a really good way to tap a wire and easy too. Soldering would be the best, but is not easy in the tight quarters by the pump there.



-Deon

 

[KMahnke]

Looked at all of my connections yesterday and everything looked good, but for the heck of it i took the scotch lock off and soldered the wire... . and yes it was a PITA . Guess the scotch lock was the problem because the missing quit and it smokes alot less. Thanks for the help!