So...my 2011 HHR LT 2.2L has proven to be a real lemon. Some of you may recall me posting about an intermittent mysterious "pop" that was occuring on cold starts. Never did track it down, and it did not occur at all over the winter. It's always seemed to be hot weather related.

Fast forward to the beginning of this summer. It's been hot here, really hot and the noise came back with a vengance. Come around July 6th it was no longer intermittent and sounded like metal hitting metal. Well IT WAS metal hitting metal, come to find out that the timing chain was slipping and the heads were smacking into the valves! So thanks to the 100,000 mile powertrain warranty (I have ~54,000 miles on it) they replaced the valves, valve seals, timing chain, timing chain tensioner and some sensors (forgot). Also, the intake gasket was blown and had to be replaced.

So now it's fixed, sort of. It seems like it's running too rich, ever notice that unburnt fuel smell when driving behind an old beater? Yeah, it smells like that. It's not throwing any codes though, which I would not expect to be the case.

Most importantly the "pop" is still there. It's much more intermittent and most of the time quieter, but still there. On occasion it will let out a resounding bang like someone hitting the engine with a sledge hammer. Again, it only happens on a cold start when the car has been sitting for a while ~8 hours and only when it's hot. It can happen several days in a row and then not happen again for three weeks.

I've started recording my starts and captured one of the quieter pops. Any idea what this is? Is this some normal quirk of the HHR and nothing to worry about?

https://dl.dropbox.com/u/71069072/IMG_0105.MOV

I'm so fed up with the vehicle at this point I'd just like it gone. Unfortunately I owe quite a bit more on it than it's worth so I'm stuck with it.

 

sounds like a small explosion in you intake.

 

Why don't you open the hood and have someone start it so you can see or hear where it is coming from. Intake or exhaust maybe something else. At the repair shop not one person could find that noise ???

 

If it were only that easy! I live on my own, so most of the time I don't have anyone to watch while I start it. Like I said it's very intermittent, so I can't make it happen on command. Two different dealers have had it for a week and they could not duplicate the issue while it was there.

 

Thats sucks, I thought timing chains were meant to last better than timing belts, belts are the ones that usually pop and cause this. In the video you could barely hear it at the end and sounds like something most people would pay no attention to. Did you ask for the parts that they replaced back so you could inspect them?

 

No, I didn't ask for the parts back. Silly me trusted them to do the right thing.

I realized I forgot to list a symptom that may be important. I've had to run on mid grade gas (89 octane) or E85 lateley, it runs like a slug on regular unleaded. I've been monitoring engine performance for the past week with a scan guage and made a curious observation along these lines.

Running on 89 octane, the short term and long term fuel trims are extremely unstable. They vary anywhere from +2 up to +10. Today I filled up with E85 because gas jumped up +$4.00 gal. The short term fuel trim briefly jumped to -16 after filling up. Other than that both the short and long term trims are very stable they stay within +1% of 0, except at startup where it can really jump. I can also really smell fuel at startup running E85. There are no evident fuel leaks.

 

Definately nothing normal about that.

 

I wanted to chime in with an update on my HHR (mis)adventure. Last Friday the 17th the MAF sensor took a dirt nap resulting in all kinds interesting codes. Had to work on Saturday morning, managed to get it to limp in. Then that afternoon hunted down a replacement sensor which was no easy task. Also decided to replace the spark plugs. Everything is good after that, actually running really well.

Then Monday morning rolls around. Go to start it and the dash lights up like a christmas tree. Engine feels like it's going to die. Pull out my code reader and get "U0073 Control module communication bus b off". Great, I really need to be at work today and don't have time for this. Try to clear the code, comes right back. Pull out of the garage and try to drive it, it moves but it's like there's a 5000lb weight behind it and the transmission is slamming into gear. Try to clear the code a few more times, turn the ignition on/off a few times and finally get a normal start. Leave the scan tool attached and monitoring for the rest of the drive. No problems.

Drive it up until Thursday and there's no repeats of it's little performance from Monday. I do however STILL have the pop on cold start a few times that started this thread. I'm traveling for business Friday and over the weekend and don't need the car, so I drop it off at the dealer. Pick it up this morning and they tell me they couldn't find anything wrong with it.

 

Hey all, I've been meaning to drop by with a final update and just haven't gotten around to it. As of 9/11 the HHR is GM's problem and out of my life. It has been replaced by a new 2012 Chevy Malibu 1LT. With the end of the year incentives and the "customer loyalty" certificate given to me by GM that made up for almost the entire gap between what I owed and what the HHR was worth.

At the end of the day I got a very nice new car, and a slightly smaller payment. I haven't owned an actual NEW car in quite some time. So I'm happy with how things worked out. I just hope I can get 100,000mi+ out of this one without any major mechanical problems.

 

good luck with the new car and enjoy. glad this worked out for you !!!