P0300 Random Misfire #2 and #7

**skyking** · 06-20-2007, 06:17 AM

'02 Camaro Z28 has been running super since I bought it. Has K&N FIPK and Corsa Cat Back exhaust. On the way to the shop for yearly inspection (can you believe it), SES light starts blinking, engine runs rough, exhaust smell. Code shows #7 lots of misfires, #2 half as much. Mechanic has now gone through most of the diagnostics - replace gas filter, clean all injectors, swap injectors, replace #2 injector with reman, swap plugs, swap coils, replace Crank Position Sensor and did two relearns. He hasn't done a smoke test for intake leaks or a compression test because two cylinders started acting up at the same time. Searching Archives on different forums has turned up both Vacuum leak behind intake manifold (although I don't think this would be specific to two cylinders) and weak/broken valve springs. Does anybody have a clue as to what might be going on? It seems I would have a better chance of winning the lottery than to have a cylinder specific item like valve springs, coil, etc. on both cylinders fail at exactly the same time. Is it possible that a sensor (O2 or MAF) could cause multiple cylinder specific problems? Thanks for any replies.

**slowagon** · 06-20-2007, 10:41 AM

Possibly coil packs? Does it idle rough?

**skyking** · 06-20-2007, 11:02 AM

You can barely tell it's misfiring at idle, it's not that bad and mechanic tried swapping coils #2 and #4, but it's bad enough to make the SES blink.

**slowagon** · 06-20-2007, 11:10 AM

If it's running rich it could be a dirty maf. How many miles are on this car?

**skyking** · 06-20-2007, 11:24 AM

It has just under 28k. Only drive it in good/warm weather up here in NH.

**slowagon** · 06-20-2007, 11:51 AM

Did you see this thread, it might help. He's expriencing the same problem.
http://www.ls1.com/forums/showthread...hlight=misfire

**skyking** · 06-20-2007, 11:58 AM

Hey thanks for the input, I just added my tale of woe to their thread, maybe someone has a clue why TWO cylinders started misfiring at the same time.

**skyking** · 07-03-2007, 03:24 AM

Thanks everyone for the ideas. Turns out the mechanic was only diagnosing #2 because it was easy to get to. Problem turned out to be a bad plug in #7 (only) so we are good to go. Misfires in #7 were backfeeding into #2 (next in firing order) so it looked like there was a problem with #2 as well. These were Bosch single tip platinums I put in only 10k miles ago. I have now replaced them with Delco Iridiums.