97 K3500 7.4l spitting, sputtering, backfires, and stalls

[Agibson]

I have a scanner with live data. Just not sure what numbers to look for and what the factory specs are.

 

[618 Syndicate]

@Dropped88 may be able to tell you what to look for

 

[Dropped88]

If the low voltage code is all your getting at ignition module would cause a sputtering issue, etc.

I would repair those grounds and verify rest are in good condition I would then check voltage and ground at ICM pigtail a see if voltage and ground is good there, could even be a slight break in wire especially if intermittent.

But at that point I'd scope the ICM signal so I could see what the PCM is seeing.

I'm not great at typing explanations but feel free to ask me any questions

 

[Agibson]

If the low voltage code is all your getting at ignition module would cause a sputtering issue, etc.

I would repair those grounds and verify rest are in good condition I would then check voltage and ground at ICM pigtail a see if voltage and ground is good there, could even be a slight break in wire especially if intermittent.

But at that point I'd scope the ICM signal so I could see what the PCM is seeing.

I'm not great at typing explanations but feel free to ask me any questions

What do you mean by scope the icm signal? Can I do this with a multi meter or test light?

 

[Agibson]

Ok I've test the voltage on power and ground wires. They both tested fine about 11.7 volts.
Moved the wiring harness all around while testing, to check for broken wires and all seems good.

 

[Agibson]

If you have access to a scanner live data would be helpful.

I finally got live data here it is.
Load_PCT (%) 2.4
ECT (°F) 159
SHRTFT1 (%) -2.3 to 1.6
LONGFT1 (%) 2.3
SHRTFT2 (%) -.8 to .8
LONGFT2 (%) 7.0
MAF 4.8 But when it started to act up it was at .02
RPM 680 to 706
Spark Advance 25
IAF (°F) 78
That's all I could get before it acted up.
Let sit for about 10 minutes hard crank to start.
Now it's been running for about 10 minutes and stumbled when give it gas. I test drove it and still stumbling.
The maf at 50mph was at 9.3 and dropped to 8 than to 6.7 stalled out and reading 12.9.

 

[454cid]

I finally got live data here it is.
Load_PCT (%) 2.4
ECT (°F) 159
SHRTFT1 (%) -2.3 to 1.6
LONGFT1 (%) 2.3
SHRTFT2 (%) -.8 to .8
LONGFT2 (%) 7.0
MAF 4.8 But when it started to act up it was at .02
RPM 680 to 706
Spark Advance 25
IAF (°F) 78
That's all I could get before it acted up.
Let sit for about 10 minutes hard crank to start.
Now it's been running for about 10 minutes and stumbled when give it gas. I test drove it and still stumbling.
The maf at 50mph was at 9.3 and dropped to 8 than to 6.7 stalled out and reading 12.9.

Unplug the MAF, and take it for a drive..... your MAF numbers are off.

 

[Agibson]

Unplug the MAF, and take it for a drive..... your MAF numbers are off.

I just want to clarify drive it Unplug or Unplug it and plug back in than drive it

 

[454cid]

I just want to clarify drive it Unplug or Unplug it and plug back in than drive it

The point is to eliminate the MAF from the system. The PCM switches the way it calculates fuel/air. It's not a definitive test, but if the truck behaves normally, it's a good indication (combined with your previously posted readings) that your MAF (or the wiring) is bad.

 

[Agibson]

It acted the same spitting sputtering and stalling