Still Have misfire

[DamageINC123]

1997 968 with 30,000 miles.

I have done everything I know to do and still getting a CEL periodicaly when running above 6,000 RPMs. Codes say 301 and 304 which is cylinder 1 and 4. I have replaced MAF and replaced plugs in 1 and 4 as well as new coil. Yes, the coils are "clicked" tight. I also ran a bottle of Techron through the tank. I do not feel the misfire which from what I hear is not unusual. Gas mileage is good and car runs perfect. Idles perfect. Plugs pulled look good.

From what I a reading I am beginning to think its a lean/rich issue. If i understood what I read correctly the ECU can only compensate for a lean or rich issue up to a certain RPM. This would explain why I never get a CEL under 6,000. I am open for suggestions. Possible air leak?

Edited January 27, 2010 by DamageINC123

[Loren]

If you only get a misfire on cylinder 1 and cylinder 4 - how could it not be related to just those two cylinders (which by the way are opposite sides of the motor)?

[DamageINC123]

If you only get a misfire on cylinder 1 and cylinder 4 - how could it not be related to just those two cylinders (which by the way are opposite sides of the motor)?

Thats why I am asking you guys and by the way thats a good point. Lean or rich why just those two. What else should I try?

[Loren]

If it is just those two cylinders then the problem is in: the spark plugs (loose?), or the coil packs (cracked?), or the electrical connectors (damaged or loose).

[DamageINC123]

If it is just those two cylinders then the problem is in: the spark plugs (loose?), or the coil packs (cracked?), or the electrical connectors (damaged or loose).

Thats exactly what I thought as well. So my trouble shooting went as follows.

Swapped coil pack 1 with coil pack 2 and coil pack 4 with coil pack 5. All clicked in and plugs tight. Same issue. Misfire 1 and 4.

Purchased new plugs for 1 and 4 (Beru Ulta OEM) Nice and snug. Same issue misfire 1 and 4

Purchased new coil packs for 1 and 4. (Beru OEM) Clicked in tight. Same issue misfire 1 and 4

Maybe damaged connectors? Why on at very high RPM? As you can tel I am at a loss. I guess I may have to bite the bullet and take it in to the dealership.

Edited January 27, 2010 by DamageINC123

[mikefocke]

10 year old wires? Cleaned end of wire going into coil packs?

[DamageINC123]

10 year old wires? Cleaned end of wire going into coil packs?

I will try cleaning the end of the wires where they plug into the coil. Can you replace the wires going to coil?

Thanks Mike

[jworden]

10 year old wires? Cleaned end of wire going into coil packs?

I will try cleaning the end of the wires where they plug into the coil. Can you replace the wires going to coil?

Thanks Mike

I'm curious - does anyone know how a misfire is detected by the control system?

thanks

John

[RFM]

Misfires are detected by the combination of crankshaft sensor and camshaft sensor. The crankshaft sensor detects a difference in crankshaft speed at the moment of the misfire, the camshaft sensor detects the corresponding cylinder. In other words, misfires are not always caused by defective coils or spark plugs, partial defective cats, valve lifters, worn cams, etc. are not be excluded as a cause as well.

[DamageINC123]

Misfires are detected by the combination of crankshaft sensor and camshaft sensor. The crankshaft sensor detects a difference in crankshaft speed at the moment of the misfire, the camshaft sensor detects the corresponding cylinder. In other words, misfires are not always caused by defective coils or spark plugs, partial defective cats, valve lifters, worn cams, etc. are not be excluded as a cause as well.

Would you say my best bet is letting a dealer look at it at this point? Should i just leave it alone and see if it gets worse. No symptoms when daily driving, just a periodic CEL when running hard (above 6,000 RPMs). The car has 32,800 miles, all service work since day one by Porsche including the 30,000 mile tune up. All oil changes with Mobile One at the dealership.

The dealership looked at back in September and said it was MAF and after cleaning it they could not duplicate. A week after I got the car back I was able to duplicate. I replace MAF myself and of course still getting the light. If I remember correctly they said something about lean mixture showing when they plugged up the Durametric software with a laptop. Again not positive but remember a conversation about lean mixture.

THANKS FOR ALL WHO HAVE RESPONDED WITH OPINIONS. YOUR HELP IS MUCH APPRECIATED!!!! THANK YOU!!