My son's 2008 HHR SS (5-speed) is having a problem.

It's misfiring when driving.

He says it stutters when driving and he smells fuel.

The codes are for misfire on each of the 4 cylinders. I doubt all 4 coils are bad at the same time.

He has a tuned computer from ZZP, along with the 2 pressure sensors. We replaced the computer and sensors with the stock units and it does the same thing.

It sounds like the computer is not getting an input (sometimes) that tells it to fire the plugs. Does the crank position sensor supply the timing signal when to fire the plugs?

This started happening suddenly about a week ago.

Any thoughts?

We swapped computers, so that's not the problem. All 4 cylinders are randomly misfiring, so it probably isn't a bad coil. We replaced the spark plugs also (the correct AC Delco Iridium) but that had no effect.

Steve

 

How about a compression test? And how's the fuel pressure?

 

X2. Fuel pressure.
Do you mean P0300 0r, P0301,02,03, 04?
All of the sensors have OBD test, no codes no problem.
If it has the display thingie you should be able to get a fuel pressure reading, The ECM can provide it to the proper computer.

 

It's an 08, so no RPD.

 

Any oil in the front cover area? On the lower left side of the front of the engine block?
did you pull the plugs , are they consistent in insulator colour?
smells fuel? Have you changed fuel lines in his car yet?
perhaps swap the coils from yours to his for testing purposes.

 

Isn't there a fuel high pressure sensor, RPD or not, that you can monitor with graph scanner? I'd do that and the a/f, while driving. No fuel low-pressure sensor, but not that hard to check. Presumably no leaking fuel under the stationary cars?

Any chance it's an E85 or E47 tune, or that someone ran E85 in it? As far as I know, from the fuel pump to the injectors and everything in between, nothing in that fuel system is meant for any more than 10% ethanol. Owners claim ethanol tunes with "no issues" but good luck with that long term. Could be rust anywhere. Does the fuel gage seem to be working correctly? Ethanol destroys the fuel level sensor pretty quickly in an non-Flexfuel car. The correct fuel pump isn't enough because a FlexFuel BCM polls the sensor less frequently to reduce galvanic corrosion.

Smells fuel where? In the cabin while driving? That would suggest a fuel leak under the hood, unless there's an exhaust leak in the manifold, flexpipe, or somewhere under the cabin.

Maybe ask you son if it sputters all the time or only "under load," suggesting inadequate fuel, supply/pressure.

 

I forgot to ask about the HPFP any wet areas or evidence of fuel?

 

It doesn't happen right away. After starting it, it drives normally for a few minutes and then acts up.

There is no chance E85 fuel (or anything other than premium 91/93 octane fuel) was put in it.

I have a BlueDriver OBD II reader that will read data and do a real-time graph of up to 7 parameters at the same time on your phone. There is a fuel pressure and A/F ratio readout.

I will get some more data and info and post back what I find.

Steve

 

We’ll wait here.

 

I had a similar issue on my LT: https://www.chevyhhr.net/forums/gene...ttering-65907/
The upstream O2 sensor was bad.