David Reich

Hi everyone,
I know this issue has been discussed many times so thank you for the patience..... that being said any insight would be appreciated as my Indy tech is stumped.

So I took my C2 on a 400 mile road trip, drove great, lots of power no issues. About two days after my return the engine began to run a little rough with a 50-100rpm low idle variance.
This issue persisted and eventually tripped a CEL P0300(General misfire) code and subsequent codes in all cylinders less cyl 2.
The oil was just changed prior to the trip.
Coil packs and plugs were replaced at in 2018

It felt like the car lost about 15% of its power in all rev ranges and choked off.

Assuming it maybe a MAS I swapped a new Bosch unit the next day. I cleared the codes and drove for about 20 min and the CEL returned on cold start up
.
Now P0300 and misfires codes in cyl 1,3,5. The idle isn't nearly as rough but CEL remains and power is decreased as is throttle response.
My Indy said when he looked things over these was quite a bit of 'blow by' but didn't know the source.

My question: Would this be AOS related( no smoke or soot in the tail pipes is present) or Fuel injectors etc?
I've heard bent valves,cam and the Vario Solenoids can be to blame...

Thoughts/ HELP please I'm going to back to the Indy today and will keep the group updated

Sporty

Bad Gas?

David Reich

I've cycled a full tank of 94 after the trip... I did think injectors if one is slightly clogged

sbbarnett

I had something that sounds similar on 2005 C2S. Injectors and fuel pump fixed it.

David Reich

Thanks sbbarnett

roadie13

Misfires are notoriously difficult to interpret, especially with high performance engines. When I had similar codes on my
M3 the first thing to check was the oxygen sensors, followed by changing the spark plugs, and then looking for small leaks in the exhaust stream.

These are all reasonable maintenance items anyway, so I would start there.

systech

Misfires on one bank only is often one of the variocam solenoids (timing or lift)

Petza914

With misfires on 1, 3, and 5 that involves both banks of cylinders so you need to look for something common to both sides of the motor, like the MAF you already replaced. I would have your mechanic smoke test the intake and see if you have a vacuum leak somewhere like at on of the plenum connection points.

What he described as blowby could very well be a failing AOS and the oil going through the combustion chamber could be fouling the spark plugs. He should pull 2 of the plugs that are misfiring and compare them to one of the ones that is not and look them over in general. Another AOS test is with the engine running to try and remove the oil fill cap. When the AOS fails it creates excessive internal engine vacuum and makes the cap very difficult to remove - not always, but sometimes.

Also, it's possible the crankshaft position sensor is failing as there is only one of those vs the camshaft position sensors that are bank specific.

JABowders

I would check plugs and coil packs, the easy way is to identify what your main faulting cylinder is causing the majority of misfires (#2) pull the coil pack and plug (inspect and compare to another cylinder) and swap it, restart the car and see if the fault follows the plug and coil pack.

I had a case where I had relatively new coil packs have micro cracks and for the most part the car ran OK, but after washer the car, or in the rain, it would start missing and acting up. And yeap, coil packs again.

Best of luck.

Petza914

I think his original note said he had misfires in all cylinders except #2 ("less #2") and then after clearing the codes and changing the MAF, got them again in 1, 3, & 5

David Reich

Today, 12:14 PM
#7
Thanks everyone..super helpful.. I'll have my indy check the vacume/AOS and plugs and swap around the coils...
He preformed a smoke tested earlier this week.. which DID NOT turn up anything.


Back in the shop later today and will have all of these items checked.

Petza914

The proper AOS test is to use a manometer to measure vacuum, which he should be able to do.

David Reich

So my Indy replaced the AOS last night. Took it on a 60mile drive afterwards. Everything appears to be back to normal. On cold start up this morning no codes or choppy idle..

Fingers crossed, thanks for the help everyone.

jchapura

I'm surprised that you didn't see "billowing smoke" out the exhaust. When my AOS went, it was like a someone "hit the switch" on a smoke machine. Scared the bejeepers out of me. Makes these things harder to figure out - almost differential diagnosis.

David Reich

I was terrified it could have been cylinder scoring. But another 40 miles of aggressive driving today has turned up no issues.

There was zero smoke or soot in the pipes etc. Indy said he could hear hissing on start up and began to dig then replaced AOS.