I have 106k on my 08 SS 5 speed and took it in for 100k checkup. Only work done was to replace plugs and clean the injectors. As I drove out of the dealer lot, I pushed it to get into moving traffic and I got backfiring and loss of power - no CEL. Took it back to dealer and they couldn't find anything - thought maybe it was just a freak occurrence. Took it home and the problem has continued. Did finally throw a code - misfires in cylinders one and two. The dealer has replaced all the plugs but there doesn't seem to be any change. Any kind of hard acceleration (10psi boost or more) causes the misfire. The CEL still doesn't come on unless I hold the throttle down while it is misfiring - I normally let up when it occurs. The misfire isn't consistent with a specific boost amount, but always between 10 and 20 psi - haven't gotten over 20 with issue. I do have the GM upgrade with plug n play connectors. RPM doesn't seem to matter either, low or high. Seems more tied to the load on the engine, regardless of RPM. Runs great when no load! I have searched through the threads and haven't found anything that quite fits my symptoms... any ideas???

 

I'd have them do a compression check, a misfire in adjacent cylinders usually(but not always)can indicate a blown head gasket or cracked head.

You might also insist on a cylinder leakdown test to check for burned or badly carboned up valves.

 

Isn't there a known issue with the crimp connectors they use for the GMTU install? Try searching "GMTU" there might some useful info, but then it's an SS and I know nothing about it.

 

Sorry donbrew. The OP doesn't have the crimp connectors as he stated he has the plug-n-play harness.

My question. Was it running OK before it went to the dealer for the 100k mile service? If so, then I would be suspect that it's something they did.

Two things I would be checking. Did they install the correct iridium plugs? There are numerous posts about our little cars not liking any other brand/type plugs than the originals.

To change the plugs, they had to disconnect the wiring/coils system. Could have damaged something in that area.

One other possibility(but I hope not) The tech took it out for a test drive and damaged something.

 

I'll check to see if they did a compression or leak down test and what plugs were installed - Thanks.
Is there any way to check the ignition system for a bad connection, broken wire, or bad coil other than replacing each part and seeing if that helps?
It was running just fine before I took it in - I know, if it ain't broke don't fix it!!! Water under the bridge now. Hoping to keep this car forever, so I thought I'd spend the money to have it gone over. Oh well...

 

THANKS FIREMANGEORGE! Even though I had asked if they were sure that they put the correct plugs in, they didn't actually check them until I brought in a copy of this thread - with your post highlighted, of course. They had installed incorrect plugs. Put the correct ones in and it runs as good as new! Thanks for the help.

 

In all reality, the thanks should probably go to the whole family of members on this forum. I learned about "wrong" plugs from reading it on this site. It really is amazing and certainly helpful on what all you can learn from Chevyhhr.net .

I also find it odd that a dealership would use non GM plugs. One more reason why I just don't have faith in dealership work.

 

Man working at a dealer and owning an SS is tough most techs are unfamiler with the HHR SS,s. We here have to help them most of the time because of what we all have learned in the forum from each other. Thanks All.
By the way my guess would have been plug wires.

 

Plug wires? Seriously? Open your hood and see if you can find them.

 

I think Thumper means the wire harness going to the plug mounted coils, I have seen the pins bent when reassembling after a plug change