VERY intermittent P03OO on 2016 Suburban LT

CLS500 · December 26, 2023

My Suburban has about 162K miles and has been meticulously maintained. Spark plugs and wires replaced at 113K miles. Brand new Wix air filter. BG or Amsoil fuel injector cleaner additive added to the fuel tank every ~5K miles.

For the past 6 months or so I have ~5 totally out of the blue blinking check engine lights that go away after a minute or so. This always happened at cruising speed of ~72 MPH. I would pull over, run a scan, and only get P0300. That is, no specific cylinder is reporting any misfire. Checked all live data from all sensors I could read- MAP, MAF, O2, barometric pressure, and fuel pressure- and they all show normal readings at idle and under load.

I understand that problems don't go away on their own and at one point have to go to the dealer. However, I am trying to do some of the low hanging fruit diagnostics myself consider the intermittent nature of this issue.

Any suggestions what specific protocol to follow to narrow the cause of this random misfire?

Thanks!

asilverblazer · January 3

If you doubt the miss fires are real, look at the crank shaft sensor.

Since you say it is well maintained, may need to look a bit deeper then. Maybe an injector is starting to underperform and is at the miss fire threshold while the engine is leaning out during cruise conditions.

The best scenario would be to have the scanner connected while exhibiting symptoms to monitor cylinder miss fire counts, or crank signal. Second best is to have someone with a laptop/scanner/tuner monitor and adjust while driving to find the cause. Practicality of those two options isn't best so it might be necessary to wait for the problem to become more pronounced so that you can effectively diagnose it.