syoo8

Hi everyone,

I'm a long-time 928 owner (and tinkerer) but inherited my late father's 996. It has 40K miles and is in beautiful condition. But...

I was driving home one day after making a quick run to the grocery store, and the engine hesitated. The CEL went on.

I checked the codes, and my OBD read:
P0306 (Misfire, Cylinder 6, Damaging to Catalytic Converter)
P1316 (Misfire, Cylinder 4, Emission Relevant)

So I dutifully changed six plugs and coils. I drove the car again and it was fine.

A few days later I started the car up again, and as I was driving down my block I got
P0304 (Misfire, Cylinder 4, Damaging to Catalytic Converter)
P1316 (Misfire, Cylinder 4, Emission Relevant)

Any advice? When replacing the spark plugs I torqued them very carefully with a torque wrench, and when replacing the coils I made sure to hear each one click.

Ahsai

Welcome to the 996 subforum.

A few questions.
What year is the 996?
Has the car been sitting? Fresh fuel? Any possibility of rodents chewing on wires?
Correct spark plugs?
Access to Durametric? Will help check for other codes and vitals like cam deviations, realtime misfire counters, etc.

syoo8

Hi Ahsai,

Its a '99 (in my signature)

It hasn't been sitting, has a full tank of fresh fuel. I'd say a very low possibility of rodents. I bought the spark plugs from Pelican and they're correct.

I don't own the Durametric. I have a simple (new) Bosch code reader.

DBJoe996

My guess is that basically two things will cause a cylinder misfire: plug or coil pack. Swap the coil pack on 4 with another cylinder and see if the problem moves with the coil pack or try a replacement. Could be bad out of the box, or something is not right with plug or coil pack. Good thing is it is narrowed down to just that.

syoo8

DBJoe, thanks for your reply.

It seems that cylinder 4 has been the problem before and after replacing the coils and the spark plugs... What are the chances that I swapped cylinder 4's coil with another bad coil... seems like it is something else.

DBJoe996

Admittedly pretty slim...but it has happened. Problem is it is something with cylinder 4 and the "easiest" thing to try is to either swap the coil packs or try another replacement. Sounds like you did everything correctly but it still has a problem with #4. After the plug and coil pack, things get much more complicated, such as the wiring harness, stuck lifters, carbonized valves, and so on. Just suggesting the logical approach to narrow down the issue and eliminate the easiest stuff first. Probably the first thing I would try is to unplug the coil pack, clean the connectors and make sure it is connected correctly (snap/click!).

mharrison

Clean your Mass Airflow Sensor with MAF cleaner. It's cheap and easy. If it doesn't help, at least you've ruled something out and have a clean MAF Sensor. You'll just need a a Torx T20 security driver or screwdriver tip.


(Hat tip to 5CHN3LL for the pic. I borrowed it from a DIY he posted.)

I had misfires with codes on mine in the past. It cleared up and ran fine after a restart, then later that week it happened again. Cleaned the MAF Sensor with CRC MAF Cleaner and it hasn't given me any further trouble for almost a year.

Ahsai

Your sig says wife's car so just want to make sure. We love 996s so much lots of ppl have more than one

Based on your answers, I suggest what Joe said about reseating the plug connection on #4. Also agree with Joe that it gets much more involved if it's not plugs or coils hence my question on Durametric.

With Durametric, you can check cam deviations, fuel trims (can indicate air leak), misfire counts in real-time (in case there are other slight misfires but no enough to trip the error codes yet). If it's cam related, it could be sticky valves, leaky variocam seals, variocam itself. All needs Durametric (or Porsche scanner) to diagnose.

I assume the old spark plugs on #4 and other cylinders look fine? Also, any oil/coolant intermix?