"Pending" P030X codes, occasional engine misfire

[Rookie48]

Yes - performed a compression test two months ago (when issue started). All cylinders were within 5% of each other (~160 psi I believe was the norm). I replaced the MAF with a used OEM unit out of another E53 3.0i that was known to have no issue. I did not replace it with a brand new unit in trying to figure this issue out.

Just FYI - this truck is throwing misfire codes (P0300 through P0306) for all cylinders at the same time. No other codes are thrown.

[jfoj]

Rookie,

You have the M54 I6 engine as I recall.

I believe the fuel pressure should be Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI? Although 45 PSI is not far off, I would be double checking this along with your gauge.

How steep is the hill you are dealing with at the house?

I will need to read back over everything again in more detail as I have many vehicles in my head that I am dealing with.

Fuel pump was replaced? If so, what brand & where purchased?

I think the Fuel System Status changing to 8 here is the key, but the question is why. This usually occurs when the O2 sensor output does not toggle back and forth and follow the engine fuel management changes. I am starting to think there is possibly some Lean/fuel starvation problem here??

I understand you say the fuel pressure gauge did not move, but often the gauges do not connect properly. Did you see a quick drop in pressure when you shut the vehicle off?

Post any Freeze Frame data you get from both the driveway and cruising if you can get it.

[Rookie48]

JFOJ:

Answers below... thanks!

Fuel pressure gauge was taped to the middle of the windshield (just under the rearview mirror), so my reading of it while driving may be slightly off. The fuel pressure gauge only moved on initial startup (truck had been off for at least an hour, lost some pressure attaching the gauge), It did not move move than 1-2 psi for the entire test drive, and when I shut off the truck, it remained at the 45 psi until the gauge was removed (about 10 minutes).

Hill at house has an initial slope of about 30%, was in 1st gear coasting, but applied a little throttle when misfire started. The hill is only 50 ft long before it levels out. I read somewhere that the DSC-X system can manage the "limp mode" but there was no actual wheel slippage (unless a bad sensor is creating a phantom issue here???).

Fuel pump was replaced by my local indie shop, I do not know the brand or where purchased (Hey Mark - if you are following this thread, feel free to jump in here! ). The fuel pump was replaced after these misfire issues started as a possible cause. Fuel filter, regulator, and relay are all new. Pressure testing suggests the engine is getting fuel properly without any starvation issue.

I will continue to gather logs....

Thanks again!

[jfoj]

Is the misfire on the hill at your house consistent? Or random?

I am also starting to think maybe a flaky cam or crank sensor?

Does the tach do anything unusual just before the misfires start?

DSC should actually take away throttle, retard ignition timing, possibly apply or modulate brakes, but should not cause misfiring.

Any chance water has gotten in and around coils or injectors? I recall the E53/E70 has some issues with the cowl leaking onto the engine.

Do you have a lot of keys on your key ring? Maybe a flaky ignition switch, I know these are know to do funny things, but would expect to see other signs.

Just tossing some ideas out.

I am scratching my head on this one as well.