silver2LT

Hey all!

So I've had my 07 HHR since new, and have dealt with some common issues I've seen around. The brakes/rotors wearing the on inner side has been a constant issue but one that can be dealt with. Up until just recently, no mechanical issues have ever been noticed.

Randomly, my SES light illumined showing a misfire on cylinder 4... not blinking but solid. More recently, I HAVE noticed a rougher idle, especially with the AC on but had chalked it off as mounts needing replacement but that may have been wrong.

So first thing I did was swapped coil packs to see if the miss switched cylinders but unfortunately it did not. I then listened to the injectors with a scope listening for anything "off" during operation or anything different between the other 3 - couldn't find anything different although the injectors weren't pulled off the motor. Fuel pressure is perfect and holds after shutdown.

Lastly, I pulled all the plugs out for inspection and to look down into the chamber and top of the pistons and did NOT like what I was seeing. The plugs all looked OK actually, but 3 and 4 plugs were of a slightly different shade of color.

What worries me most is how uneven combustion is occurring. Cylinders 1 and 2 look absolutely immaculate, they are darn near spotless inside - I can even read the markings on the tops of the pistons it's so clean in there. However cylinders 3 and 4 DO NOT look anything like their running mates. Cylinder 3 has a DRY, thick black pile of carbon deposits all over the top of the piston and the markings on the piston cannot be read. Cylinder 4 is the worst with WET, thick, black carbon deposits on the piston. This tells me that cylinders 3 and 4 have been missing with 4 missing much more and 1 & 2 not missing at all.

I am highly suspecting the valve guides have come loose in the head and the valves on 3&4 are not always seating and thus, misfire occurs. What's even more troublesome is this is the 6th year of the 5/100K PT coverage but the vehicle was always light duty with all services performed. The vehicle on has 52,500mi on it!!

This is too young of an engine to have this issue so I wrote to GM and we've been playing phone tag but am suppose to talk with them Tuesday about it.

I know I'll need a compression and leak down tests but am waiting until I talk with GM in case they should be done at the dealer.

Does it sound like I'm on the right track here? I can't find a single reason for a miss at this point other then mechanical failure

Thanks for looking!

843de

You're working through the diagnostic process very logically, and that's to be applauded.

I'm assuming you pulled the codes, or had them pulled, what code/codes has it set? They can be a great help in narrowing things down a bit more.

Regardless of what GM proposes to do, I'd go ahead with your own compression/leakdown tests. Done properly it won't exacerbate the issue, nor will it invalidate the warranty/goodwill coverage from GM.

Since cylinders 3 & 4 are not "steam cleaned", the probability of a cracked head or blown gasket seem low, but a compression/leakdown test will either confirm or deny that possibility.

My thoughts are going towards valve guide failure, or failing injectors on those cylinders.

silver2LT

Thank you, most service I do perform my self, maintenance and repairs typically. So I do know my way around or can find my way anyway :)

Yes, I pulled the codes with just my OBD cable and Netbook, only code listed was P0304. I had cleared it, swapped packs and tried again. Within 2-3 minutes of idling the same code returned (P0304) so that's when I did the other items I mentioned previously to get where I am now.

I agree that a crack in the head and/or gasket is likely low, especially considering this vehicle really has been babied, but serviced like a fleet vehicle with respect to fluid and filter changes. (I own 4 vehicles and I usually do all service at the same time regardless of condition) There are no coolant system related issues or cooling system pressure problems that I'm aware of.

I need the proper adapter for a compression test, what I have now I don't think I could get threaded down into the deep well. I'm going to head over and buy a new tester and report back with compression test results and then based off that, will do a leak down once I get an adapter built for that too.

I'm trying to gather as much info. as I can come Tuesday when I speak with GM. I am sure they wouldn't take my word for it and will need their own set of diagnostics which was why I was holding off on doing mine right away but I agree, no reason to wait on compression tests.

Thanks again

843de

A healthy Ecotec should have between 155-180psi in each cylinder on a compression test, GM specs state that there should not be more than a 70% variation between the highest and lowest cylinder.

If you find that cylinder 4 shows 100psi or less, that's a fairly good indicator of an issue with the valve seat, valve, or valve guide.

Of course with the added possible involvement of cylinder 3, a cracked head may still be the culprit.

Having your own numbers to compare with the numbers obtained by the GM tech will prove invaluable.

donbrew

I know you said no coolant probs but, Were the insulators (the porcelain part) on 3&4 orange? That would indicate DexCool in the combustion chamber.

silver2LT

Excellent, I will use those values as a reference.

I will have to snap some pictures when I have everything out again. I noted all the plugs looked actually quite good. 1 & 2 were very clean with some light gray on the porcelain while 3 & 4 also looked pretty good actually but had more of a light brown residue on the porcelain, I would expect that I would have noticed dex-orange colored deposits but not hard to look again.

I've got to run and see what I can find in the store, ill check back later thanks.

silver2LT

Quick question, how can I open the throttle on this drive by wire system? Will putting my foot on the pedal actually open the plate for me to do the test accurately?

donbrew

A TechII scan tool, or a lovely assistant. Those are the only choices.

843de

Personally, I always prefer a "Lovely Assistant" over a Tech II when activating the "clear flood" mode.

You can do a compression check with the throttle closed, but its better to have a WOT so the engine can breathe.

silver2LT

Thanks for the advice, as it turns out with the key on and foot pressed on accelerator pedal, the throttle blade opens as you might expect so it wasn't a problem. I was pleasantly surprised at my readings which were: cyl1-166psi; cyl2-169psi; cyl3-166psi; cyl4-168psi these were taken on a semi-warm engine. It had been ran up to temp and then cooled enough to work on. I cranked the engine 6 rotations per cylinder each time. Those are perfect readings, any need for a leak down? I put new plugs in since I had the old ones out and cleared the code once again. Has not returned but its only idled in it's parking place, hasn't gone anywhere so I'll have to see if that makes any difference. Seems to run exactly the same.

I don't really see anything in the old plugs...
Plugs 1
Plugs 2