Hello guys I've Had my HHR for a couple of months now running perfectly fine but unfortunately I've been having a issue where only 1 cylinder which would be cylinder 4 misfire at a certain rpm im fairly new to the lnf motor and turbochargers in general my last car was a 4runner so I've been diagnosing a lot of this stuff by myself my brother has a cobalt ss but couldn't really tell what the issue could be here's what I've done so far compression testing came out good spark plugs have been replaced with oem spec ignition coils also replaced also oem injectors have been cleaned and checked running well I've been doing my research and i have yet to see this issue there's some similarities to some other people on this forum but different outcomes some people have bad compression and some bad spark plugs the only thing i could really think of was the hpfp but i don't want to jump the gun before i do anything else almost forgot also switched to a new maf sensor and when i drive the car it also flashes the check engine light when i go over a certain rpm when pressing on the pedal a little to hard to hit boost

 

A flashing CEL means something horrible is wrong. Freeze Frame data and the exact codes might help. If it is when boost starts, that pretty much narrows things down to the boost system, maybe a leaking intercooler.

There should be pending or historic codes that could help

 

to the forums!

So the code you're getting is P0304?

Sounds like you've covered everything. All I can add is that the injectors on the LNF are much more difficult to work with than on the 2.2/2.4. It involves special tools, I think a reamer, among others. If you thought that the procedure was the same, you probably have leaky injectors.

I don't think I have read about anyone cleaning them and reinstalling the old ones. The amount of work involved, it makes more sense to install new injectors.

But you installed ACDelco 41-108 spark plugs?

 

Possible coked intake valves, or intake manifold leak.

 

What were the numbers? Did you do a running compression test which is most relevant for off idle misfires.