tsjoel

My Check engine light is on and the computer says I have a p0300 random misfire detected and a p0301 misfire cylinder 1, p0302 for cylinder 2 and so on thru 6. The car runs great and I do not notice anything unusual. I have had it reset twice and it keeps coming back. I replaced the battery just as shot in the dark because the problem occured after the alternator belt broke and I had to drive it home and to my shop using just the battery.
I have searched this topic and I have PMed a few people to see what their solutions were and Curtis 97 targa fixed his with a new control unit. I am not sure what control unit if might be (are there more than one?). I am sure there are other people that have had this problem and found a solution. I have a feeling I could spend a boat load of money taking shots in the dark. BTW my spark plugs were just replaced before this started happening. My shop uses the OEM spark plugs. Thanks in advance for your help.

Ben in Plano, TX

I had these codes and it turned out to be a failing Dual Mass Flywheel(DMF). When the transmission is nice an warm do you hear any gear clatter with the car in neutral and the clutch pedal out? Does the clatter go away when you depress the clutch pedal?

Those are the symptoms of a failing DMF - ironically - it sounds like the Light Weight Flywheel (LWF) does when you put that in.

The misfire codes are generated in this case because the crank position sensor looks at the teeth in the flywheel to determine misfires. When the DMF is failing the rotation of the flywheel is not smooth under some circumstances and the DME interprets that as cylinder misfires.

I had the problem iniatially only at DE's then it progressed to normal driving. THe gear clatter slowly grew more noticeable. I have installed the LWF and now have all the gear clatter but no more CEL.

Ben

tsjoel

Ben,
Thanks for the response. I do not have any gear clatter warm, cold or otherwise. I know everyone is looking for a reason to install the LWF but I do not have any of those symptoms...... yet

mbriggs993

I had a similar situation where my check engine light was on with misfires at various times on various cylinders. My car also ran great with no problems. The problem started after my 30,000 mile service. The check engine light would only come on under fairly hard acceleration around 3-4,000 rpms. The dealer replaced the distributor and caps, spark plugs, spark plug wires and fuel infectors. None of that made any difference, the light still came on under the same conditions. The dealer consulted with PCNA all along the process and finally replaced the alternator, fan belts and pulleys. That did the trick. It was explained to me that somehow there was an issue with the alternator or belts and it made the engine think it was misfiring. That was about 7 months ago and I have not had any problems since. Since your problem began when your alternator belt broke it sounds like it may be the same issue. Hope this helps.

Sachin Misra

I had misfires after the supercharger was installed. Changed the plugs, wires, ignition coils and both the distributors (not just the top). No misfires since then.

Lorenfb

"The misfire codes are generated in this case because the crank position sensor looks at the teeth in the flywheel to determine misfires. When the DMF is failing the rotation of the flywheel is not smooth under some circumstances and the DME interprets that as cylinder misfires."

This is the method used to determine a misfire, i.e. the DME monitors the flywheel de-accel
to determine a loss of a cylinder's power contribution which equals a misfire.

"The dealer consulted with PCNA all along the process and finally replaced the alternator, fan belts and pulleys."

This is one of the more common solutons I've seen at some of my independent Porsche shops.
I've confirmed this with one of my Porsche dealers who states that non-Porsche belts
cause alternator vibs which are detected as a misfire. Maybe a little hard to believe, but it
solved the problem.

tsjoel

I think there is a rs-pulley that will run the fan and the alternator with the same belt. Do you think this might solve the problem? How would I know if the alternator is bad?

Lorenfb

Just put the Porsche OEM belts on.

Monique

Although the RS pulley is an original P part too. Some issues are present if you have a highly optioned car. Too much demand and too little juice as the alternator does not rev as quickly with the smaller RS pulley. FWIW

tsjoel

My shop uses OEM belts. I wonder if there could be some slippage.

Lorenfb

"My shop uses OEM belts. I wonder if there could be some slippage."

OEM belt - One which comes directly from a Porsche dealer's part bin & not from
a Porsche parts supplier, e.g. SSF, Woldpac, & IMC.

Verify the belt yourself and don't make assumptions!

ElCid86

Note to anyone doing the serpentine belt. Use a Porsche belt from the dealership. I bough an aftermarket belt Dayco belt from a local auto parts store and within a thousand miles developed misfire codes on all cylinders: P0300, P0301, P0302, P0303, P0304, P0305, and P0306. (yes it is hard to believe and harder to explain that a belt can cause misfires but there were several cases reported here and Planet-9 so I gave it a try and swapped to a Porsche dealer purchased belt. Misfires are gone and I have put close to 1000 miles on the new belt to include spirited fun runs, Auto-X and long highway drives.) I'm sure others have replaced with Dayco or Continental belts without issue, but it's not worth taking the chance on having to do it twice imho.