hey guys. this project of mine just keeps getting worse the more i dig into it. my newest issue is. when cold the truck sputters, spits, and backfires wont go above 15-20 mph but once warm it runs like a champ. this all started after i put in the Hughes Plenum kit. i finally got it to throw a code and i got the p1391 manufactor control ignition system or misfire. the fireing order is correct all the plugs and wires are replaced new crank sensor and coil. and i replaced the o2 sensors after i did the the plenum. i was so close to having this truck finished. so before i dig into it again just thought i would ask to see if anyone has had the same issue or knows how to remedy it. any input is greatly appreciated .

thanks
B

 

Mine does pretty much the same thing. Bogs, misses, and generally runs like crap when it's cold, but, run it for even a few minutes, and it's fine....... So far, I have checked:

Plugs: Fairly new, fairly clean. Nice even tan color, some ash deposits on 1 and 8. (another problem altogether....)

Wires: In good shape.

O2 sensor: New.

Plenum: Hughes plate, and modded.

PCV: new. (dealer part.)

Cap/Rotor: Also new.

Fuel Pressure: 47lbs at idle cold.

Coil: New

No codes, run it for just a few minutes, and then it's fine..... I have no idea what is happening there. MAP sensor might be suspect, but.... I would think that would give more problems, and possibly set a code.

I suspect it may be due to compression loss on one or more cylinders until the pistons/rings heat up, and seat a bit better..... need to do a compression test, but, I have been avoiding that, as I suspect it is going to tell me things I don't wanna know.

 

To the OP, what brand 02 sensor did you use? Might try putting the old one back in and resetting the pcm, assuming it did not act the same on the old 02 sensor.

 

Thought I would add to that, on my other truck, 01 1500 3.9, I had erratic idle and anytime I would come to a stop, it would stall out. I would have to keep the truck running with giving it gas while being stopped. Garage said MAP sensor and it never threw a code or CEL... Never had a problem after they fixed it.

 

I thought when the vehicle is cold its in open loop so the 02 sensors dont have anything to do with how it runs until it goes into closed loop. It's running on preset peramters on start up. is this true or not?

 

Yes, it is. For the most part. We have heated O2 sensors though, so, after about two minutes, the PCM starts paying attention to them.

 

My thought was, it didn't do it before you fixed the plenum, changed 02 sensors, plug wires, etc. Fixing the plenum shouldn't be the problem if it was done right, so I'd be looking at the other parts I changed. Out of the parts changed, the 02 sensor would seem to be the only one where engine temp would directly come into play.

 

Do u have a clogged cat ? Try running the truck withoutt the pre sensor

 

ugggh. this is killing me lol. thought for sure i had it figured out changed out the tps. it runs better but still chugs and backfires until its in closed loop. so im about to take it back apart and start from scratch. i had thought it may have been the cat due to others having and issue with it clogging after doing the plenum. but if the cat was plugged it would run like crap all the time. i had one plugged on my 94 1500. and ive tried putting the old O2 sensor back with no difference. plenum is done correctly. no leaks anywhere. the only good thing about this is. i have a completely brand new all the way through ignition and a few new sensors. so with the truck only having 94k it will be sitting pretty if i ever figure out what the hell is causing it....

 

P1391 Interm Loss of CMP or CKP .