Who can decode the codes?

At VIR in November: Check engine light comes on. Codes P0306 (cylinder 6 misfire detected), P0154 (Sensor EKT no activity), P1318 (manufacturer controlled ignition system or misfire). This happens after black flag, engine shut off when still hot and then restarting 1 minute later.

Found loose coil pack cylinder 4. Codes reset: back on track, check engine light back on: P0154 (O2 sensor circuit no activity detected (bank 2 sensor 1), P1318 (misfire cylinder 6 emission related)

Replaced coilpack for cylinder 6. Back at track. Check engine light back on after hot restart. P0300, P0306, P0301 (cylinder 6 and 1 misfire), P0158 (O2 sensor circuit high voltage (bank 2, sensor 2), P0154 (as above), P1313 (unknown)

Reset codes and drive on street: no issues.

Lots of clues, anyone got a guess on what needs to be fixed?

 

Emissions relevant misfires point to improper/incomplete ignition which subjects the converters to unburned fuel which will burn in the converters and overheat them with resulting damage.

You replaced the #6 coil pack and yet that cylinder misfired again.

Street driving may not subject the engine to operating conditions that will bring out the worst in marginal plugs/coils.

On the track... it is a different story.

Which reminds me: What about the plugs?

What are the conditions of the plugs? Are they the right ones for your car, its engine? Are they relatively new? Installed properly? Are the coilpacks secure to the engine and to their respective plug?

I also question wonder about the quality of the gasoline. Track usage should have the tank filled with at least the best street gas you can find and of the proper octane grade and even better is if you can put in some lead free racing gas of say 100 octane. This is too high in that the engine can't make use of the extra octane but the higher octane will make detonation less a possibility. Also you want to be sure you are buying *fresh* gas. Premium grades of gas go off (become stale) quicker and in some cases are little better than lower octane grades of gas when this happens.

There is also the issue of the O2 sensor errors. IIRC the error code points to a sensor heater problem. The heater may be bad or there may be bad wiring/connector at the root cause. (Most often it is simply the sensor that's bad.)

Improperly heated (too cold) sensors are sensors that do not operate properly. These can affect the fueling of the engine. To the point emissions relevant misfires occur? I can't say for sure.

But if the sensors are bad, or questionable, you might consider fixing more obvious symptoms. One less variable.

Sincerely,

Macster.

 

Still working on it...
The national consensus seems to be that there are solder issues in the ECU - an apparent problem with 1999 996s. The ECU is being sent off to Florida for repair. Hope this works!