Need help on a misfire
 

P0303 cylinder #3 misfire. I have no clue what is causing it.

Background - Swapped out almost everything for this build. Majority of it is in my signature. Code gets thrown at startup, when I would clear it, it would never come back on during driving. Didnt matter if it was 100 miles, or 2 miles. But at startup the code would come back. We moved the spark plug to #4 and the coil to #2 and still got the P0303. We did a compression test, 130 across the board. Tested for injector pulse on startup for cylinder 3, that was good and normal.

Switched the spark plugs from the auto lites that ZZP sent, to OEM AC Delco gapped at .030". This is where I am at now. CEL was gone for a day or so and is now back. I have an interceptor gauge so I watched misfires and it only registers a #3 misfire at idle. If I am in gear and driving it shows nothing, once I am idling that number starts climbing. Once I start driving it goes back to zero. If I clear the CEL it does not come back on untill startup, but now it is 2 startups after its cleared.

What else can I do? It doest drive odd, it doesnt have any issues while driving. I went back and forth and tuned it with Matt from ZZP, he cant see anything odd in the log. Any help is appreciated.

After I get this all situated I am going to throw it on a dyno and get numbers.

Swap out #3 injector next

That would be a difficult task with the OPEL injectors wouldn't it?

Crap sorry I am mistaken, you're LNF direct injected...it's a big job to swap injectors. With PFI it's much easier to swap injectors so why I suggested that first.

I mean if all that is left to check is the injector then I have to do it I guess, which means back to ZZP for a new one and all that jazz. Any other thoughts before I go that route?

If ignition and compression are not it, it's the only thing left.

But if it was an injector, why would it only happen at idle? That is the only thing that is odd.

Restricted flow and then once the rpms climb the fuel pressure overcomes the clogged ports in the injector

130 across the board is kinda low for lnf. should be 150. or did you do it on a cold engine?? ur supposed to warm it up first fyi. if you did, get a new compression tester.
I think literally everyone gets misfire on startup on modded and tuned engine at some point. I sure do. its in the tune. fix the tune, and ur misfire will go away or pop up less often.