Misfire and rough running 98 k2500 5.7

[jaxcob]

Dude check the fvkc!ng MAF (and forgive me is you already gave it a visual)! I guarantee that's it. If it looks OK unplug it and go for a rip and come back to tell us how awesome the truck runs.

You can try cleaning the MAF but not likely to help in my experience.
If you do make sure to use MAF cleaner ONLY.

So y'all are the best! I had looked at it and its clear and clean looking but unplugging it seemed to take the severe misfire away. Fuel trims are back to being under +-10% both banks. It's still a bit stumbley and doesn't like anything under 2k rpm but it actually will move itself now. Such a relief guys. Thank y'all so much. Any specific replacement brand you'd suggest that I could pickup tomorrow?

 

[wirlybird]

Personally, I went with Delco and not a rebuilt but new. May be some other mainstream brand that are good, but I am not sure. Just not rebuilt.
Once a new one was plugged in it did seem to take little driving for things to settle back down.

 

[Schurkey]

Too much emphasis on fuel trim numbers which mean nothing when there's a misfire or seven. Misfire creates a false "lean" condition at the O2 sensor, causing the fuel trims to go rich.

Verify the rest of the sensors. The scan tool should give you ideas on how they're all working, including the MAF.

(Once he fixes the coolant temp sensor, can he not merely unplug the MAF, force open-loop, and see how the truck runs? If it runs better, the MAF is toast?)

 

[jaxcob]

Too much emphasis on fuel trim numbers which mean nothing when there's a misfire or seven. Misfire creates a false "lean" condition at the O2 sensor, causing the fuel trims to go rich.

Verify the rest of the sensors. The scan tool should give you ideas on how they're all working, including the MAF.

(Once he fixes the coolant temp sensor, can he not merely unplug the MAF, force open-loop, and see how the truck runs? If it runs better, the MAF is toast.

Appreciate it, I'm better with carbs and Mopar than the GM stuff. Not really sure what to watch and I did a lot of reading today lol Unplugging the maf definitely did improve things and I have one ordered. I'll pick up the info with time, just haven't been exposed to a GM newer than a 94 tbi 1500 back in highschool.

 

[jaxcob]

Well new Delphi maf, Delco water temp, and napa premium wires and no dice. Still weird misfire that sometimes shows up on cyl 1 & 4 on the dash command. Pulled the plugs and swapped 2&4 and 1&3 and no change. Still showed as 1 & 4. Maf is showing better response in the app. But possibly plugs now? Can they just die suddenly? I know I'm chasing my tail a lot and throwing parts at it but I did ohm the old wires and new ones as I switched them and did have a couple dead ones so changing them was justified in my mind. Assuming they died when I was pulling them so much before. The truck is watching this thread it seems.

 

[jaxcob]

New plugs and maybe a little in a positive direction? Maybe a little smoother but also I could be hearing what I want to hear. Still has a misfire and will barely accelerate down the road. Just doesn't have the pep, it's like it has to fight to go. Also the misfires are isolated to 1&4 now according to dashcommand. I'm at most of a loss right now but I might try the old cap since the new Delco one won't get here until next week.

 

[jaxcob]

I'd also like to reiterate that the whole episode that lead me here happened while driving home after a day of running just fine and no issues. And it's been at least 3 weeks since I changed the poppet injection out for the mpfi style and it ran perfectly up until that evening

 

[jaxcob]

Dude check the fvkc!ng MAF (and forgive me is you already gave it a visual)! I guarantee that's it. If it looks OK unplug it and go for a rip and come back to tell us how awesome the truck runs.

Hey, so new MAF and plugs and wires and still having issues. Could a clogged fuel filter or weak fuel pump be causing these issues?

 

[Supercharged111]

Hey, so new MAF and plugs and wires and still having issues. Could a clogged fuel filter or weak fuel pump be causing these issues?

Strange. With the MAF code and symptomology I would have put money on it. What's your fuel pressure like?

 

[jaxcob]

Strange. With the MAF code and symptomology I would have put money on it. What's your fuel pressure like?

That is tbd right now. Haven't got a tester but plan on having one soon. I do know there's pressure at the Schrader valve after sitting all night.