Chevy HHR SS Random Misfire update. The car ran nearly 2 months and 2k miles with no cel. Yesterday the wife said the check engine light came on (she didn't notice any obvious stumble to the car) but the 5 typical cel's were on P0300, P0301, P0302, P0303 and P0304.
I took the car out for a drive and on the first shift from first to second gear, car had a major series of stumbles, nearly stalling out. After about 10 secs. the car smoothed out and appeared to run fine. Checked the cel's and there was a "new" P0101 (MAF sensor out of range) in addition to the 5 typical cell's. The MAF is relatively new (changed out by a dealer 4 month ago). Any thoughts? If there is any info I can provide (I have a simple scan tool and can view the live data)?

 

Fuel pressure? The swoosh sound may be something in the turbo.

 

donbrew,

Thanks for your replay. Tested fuel pressure is 67 psi from the tank to the inlet of the high pressure pump. I think that is in spec? It doesn't mean that the high pressure pump doesn't have a problem, but looking at LiveData on a scan tool it looks ok.

 

Coked intake valves, wrong , dirty, incorrectly gaps spark plugs.
These are a few things, loose wires.
Are you running a tune?

 

Completely Stock....no tune. Plugs were changed by dealer, also about 4 months ago.

 

When it stumbled, were you babying it or were you getting on it?

You never did say which spark plugs were in it.

 

I had a misfire on cylinder 3 that was caused by a bad coil pack. I was able to consistently make the problem appear by jabbing the throttle, letting off slightly, then jabbing it again. On that second jab, like clockwork, I got the flashing CEL and the stored P0303. Changed plugs while I was in there and its been great since. My car in particular doesnt like you to let off the power until it wants you to, I dont know why. I attribute it to the way the throttle plate communicates with the pedal, Who knows. Its been fine for nearly a year now.

 

Plugs are: ACDelco 41-108. I wasn't "getting on it" just normal driving. It occurred during the shift of the manual tranny from gear one to second gear. Coil Packs were also changed by dealer several months ago.

 

A compression test and leak down test would be my next step

 

The compression test in November looked good.

HPFP, dirty fuel rail, or injectors, don't know what else it could be. Maybe a really dirty throttle body?