Odd Misfire issue. No Codes. Any insight?

Josh@DirtyDiesels · Dec 16, 2013

So Lately I've been having a really weird misfire issue with my truck. If you aren't familiar with my build I am running MPD 305/150s and a s475... Just installed a new hpop a few weeks ago, BUT, it started doing this before that. The truck runs awesome when just driving it around and not really hammering on it, but if I hammer on it hard or do a WOT pull it will start misfiring and feels like bad injectors for a little while. Sometimes it will go away quickly, and sometimes it will keep misfiring for awhile. No codes thrown when this happens. Have ran it with a scanner on it and when it happens it shows low contribution for a few cylinders but then it clears up randomly. Has me stumped. The one theory I have is potentially lpop not keeping up and oil cooler maybe getting drained after a hard pull and introducing air into the system?? Any thoughts, ideas, tips??

powerstrokin15 · Dec 16, 2013

probably the muffler bearings or the dildo lug covers you have on those stockers.

Josh@DirtyDiesels · Dec 16, 2013

powerstrokin15 said:
probably the muffler bearings or the dildo lug covers you have on those stockers.

***k off homie. Most likely the muffler bearing delete kit causing it. but for real though this is pissing me off

Sysx · Dec 16, 2013

I wasn't modded like you but my truck did that when my fuel pump was going out.

Finally from a phone that fits my hands!

Josh@DirtyDiesels · Dec 16, 2013

Sysx said:
I wasn't modded like you but my truck did that when my fuel pump was going out.

Finally from a phone that fits my hands!

I did think fuel pump but I have a fuel pressure gauge and am watching the pressure off my regulated return. NO drop in pressure ever. I would think that if there is a flow issue it would show in the fuel pressure gauge?

swinky · Dec 16, 2013

Do you have a sump?

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swinky · Dec 16, 2013

Is it the same cylinders every time?

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Josh@DirtyDiesels · Dec 16, 2013

Yes I have a sump. Only had the scanner on it once and it was cyl 7 and 3

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HOOV3R · Dec 16, 2013

Icp doesn't fluctuate rapidly during the miss does it?

Josh@DirtyDiesels · Dec 16, 2013

HOOV3R said:
Icp doesn't fluctuate rapidly during the miss does it?

Honestly couldn't tell you right now. I have a live wire ts in it now which doesn't read icp voltage so I can't really tell. What is weird is that after running it hard it will start missing and then randomly start running fine again

HOOV3R · Dec 16, 2013

Icp fluctuations can cause cylinders to have a low contribution, making it seem like there is an injector issue when there is not. Could be an Ipr issue. Need to monitor Icp, Ipr duty cycle etc.. while the miss occurs.

sootie · Dec 16, 2013

And I believe 3 and 7 are next to each other in the firing order so the miss may only be occurring in one of those cylinders.

Josh@DirtyDiesels · Dec 16, 2013

HOOV3R said:
Icp fluctuations can cause cylinders to have a low contribution, making it seem like there is an injector issue when there is not. Could be an Ipr issue. Need to monitor Icp, Ipr duty cycle etc.. while the miss occurs.

I need to get a scanner on it and do that. I wouldn't be surprised if it was the ipr

swinky · Dec 16, 2013

sootie said:
And I believe 3 and 7 are next to each other in the firing order so the miss may only be occurring in one of those cylinders.

1 2 7 3 4 5 6 8. Correct.

Josh@DirtyDiesels · Dec 18, 2013

Watched IPR duty cycle today while the miss was going on. When it was running normal I saw a max duty cycle of about 85% and when it started misfiring the duty cycle was between 20% and 45-50% tops. Maybe bad IPR? Also when it was misfiring the duty cycle seemed pretty slow to change and hung up sometimes.

HOOV3R · Dec 18, 2013

dzlpwr said:
Watched IPR duty cycle today while the miss was going on. When it was running normal I saw a max duty cycle of about 85% and when it started misfiring the duty cycle was between 20% and 45-50% tops. Maybe bad IPR? Also when it was misfiring the duty cycle seemed pretty slow to change and hung up sometimes.

What was the pressure doing during the miss also?