2007 5.3 misfires, rough idle, no other codes

torquemeister · January 5, 2020

The only code is for the MAF being unplugged. If I plug the MAF back in, I get misfires on 7 & 8 and just a P0300 code. With MAF out, just MAF error. Compression was good on all cylinders - that was the first thing I checked when all of this started. I don't remember the actual readings now, but I believe all 8 cylinders were in the 145 - 160 range.

Thanks,

-Chris

sefiroxx · January 5, 2020

MAF at warm idle is 2-7, you are on the high side. At 2500 rpm, you are on the high side. O2 voltage at.85 indicates rich.

Computer on initial fuel rate calculation uses the MAF reading to set fuel rate to achieve 14.7. It then looks at O2 to see results and adjusts.

Sounds like your MAF is reporting too much air. Computer adds extra fuel. The total air actually taken in used up by the front cylinders leaving the two rear cylinders starved for volume, and what little they get is too rich.

torquemeister · January 7, 2020

Thanks, that explanation makes a lot of sense. It still runs pretty rough, even when it doesn't throw a code (while the MAF is unplugged). Makes me wonder if there is an issue that will have me taking the valve covers off as previously suggested. I'll start looking at replacement MAFs. Anybody have and experience with the cheap ones online? Or just suck it up and go with OEM??

Thanks,

-Chris