Misfiring cylinders 4, 5 and 6
 

Hello Everyone,

I am new to this forum, as I have recently purchased a red 986 2.5 Boxster from 99, with 94k Km.

However, I have some issue with it, and the mechanics I have been to have not helped me up to now, so I turn to the community to help me diagnose the problem.

I have 4 error codes on the car, Random Misfire (P0300), and Random Misfire cylinders 4,5 and 6 (P0304, P0305, P0306). So basically, I have one bank of cylinder that is not working. The car idles with difficulty when cold, and has about 1/3 of the horsepower it should have even hot, but still runs. Even when hot, putting the AC on will stall the engine in idling. When the engine is starting, it randomly makes between 1 and 5 time a big knock, like if you tap two metal parts together, during the first 30 seconds. It also farts dark smoke randomly when cold.

I have changed the Spark Plugs and Ignition Coils without conviction (since it's all 3 cylinders on one bank). I am soon receiving a MAF, but I don't thing it's the issue since it would affect all 6 cylinders.

So I am looking for your experience to help me. I am thinking about injectors (but why 3 on one bank?), air/oil separator (why not all cylinders then?), or head gasket seal?

Do you think that the symptoms indicate one of these problem, or maybe something else that I have not think of ? Maybe one of the thing I listed cannot be the cause and I would waste money changing them now ?

Thank you in advance.
Nounoon

That's odd, I only fart dark smoke randomly when I'm warm.....

Check your oil filter. Any debris at all? I'd stop running it until I had a better idea what's wrong.

I don't drive it anymore except to drive to the shop. The oil and oil filter are new. If I find little debris it basically means the engine is ruined?

I had a p306 misfire due to a loose fuel injector wire.

Lots of possibilities. It's air, spark or fuel so look at all three. Electrical issues are the first place I would look. Rodent damage to a wire harness? Year? model? mileage? Any recent work done that might have affected one bank?

Best not to run the car until you get some better intel. Misfires tend to kill these engines very quickly.

It is a 99, 2.5 non S with 94000km. It did't have major work recently, and the Spark Plugs and Ignition Coils were changed after the problem started.

How did the old plugs look? Sooted, tan, whitish, oily?

Unfortunately I didn't do this work myself so I don't know :-/

Would 2 coil packs mixed up cause this?

I don't think so, I changed all 6 coils this weekend and it didn't change anything.

Do you have a Durametric? Is that the only code you see? How are your cam deviations? How about RKAT readings?
I would also suggest rechecking your wire connections into the packs. These need a little finesse to assure that they are properly seated (making a good connection). I had this problem recently and the cause was just that!

Nounoon, did you resolve this? I have almost exactly the same problem (same codes). Mine starts and idles OK, but misses just off idle until warmed up. I've replaced all plugs and coils, as well as fuel pump and fuel filter for good measure, but I still have this issue.

HI NOUNOON
hello!
I am also new to th forum and glad to see the same feathers!
I also drives a 2015 porsche bolster which had the same issue-it got resolved by changing the coils though…please ask your service technicians to interchange the coils and see if the coil is the real culprit.you might get error code and the system also allows you to drive.when you swap the coils between misfired cylinders and running cylinders, the error coding must show the shift to previously running cylinders….then its confirmed the issue is with the ignition coils…i did this exercise and confirmed about the coils and got it changed and the issue was resolved.all the best and happy motoring!

Hi,
I tried with a OBD-II reader, to check the real time values of the different sensors. The issue on my car was the O2 sensors that where dead, so the car didn't know how much air/fuel to put in the engine. I had a similar problem weeks after solving this issue, and it was the oil/air separator that had issues. Now the car is working well.
I was afraid it was the IMS, if it's that, I was told the car should make a "cling cling" sound similar to a chain touching something.

Same thing happened to me.