CEL Repeat Issues
 

Hello everyone.

I purchased a 2003 Porsche 911 Carrera 4 Cabriolet with 106,000 miles back in October, 2018. For the first month or two, I didn't have any issues, but now it seems to be one thing after the other. The first problem occurred on November 8, 2018 when the car threw the following CEL codes (solid): P0300 P0306 P0304 P0305, seemingly related to misfires. I took the car to the dealer and they said that the misfires were "caused by cracked coils" and they replaced all six, which came out to $915.37 parts/labor. The dealer also stated the 60,000 mile maintenance hadn't been performed, and recommended I do this (I declined at the time). After the coils were replaced the car ran fine for another two weeks and then the check engine light came back on (11/26/18), this time with the same CEL codes as before. This time the dealer said that the misfires were due to the spark plugs, specifically "wrong plugs and worn out electrodes", which they replaced for $198.62 parts/labor. Once again the car seemed to work fine for about a month, but when I went to turn it on one morning, as I pulled out of the driveway the car now threw a flashing CEL and white smoke was coming out the tailpipes. I immediately turned the car off and had it towed to the dealership. They determined the battery was completely dead which "caused all issues regarding run conditions". I had them throw in a battery charger along with the new battery for $571.14 parts/labor. Go figure, the CEL is back on (solid) yet again, but when I took it to the dealer they said the fault wasn't actively occurring (they did see a past fault for random misfires -- my reader showed CEL codes P0300,P0305,P0304), so there was nothing they could do. As I picked up the car from the dealership today, I noticed it seemed to misfire again but didn't throw the CEL yet. So far the misfires only seem to occur on startup after the car has been sitting for a few days, and when it's cold outside (could be unrelated). At this point I'm out of ideas to try, but I was going to take the car to another independent shop and see if they had any advice.

Thanks in advance.

Looks like you're getting solid misfires on bank#2 and since they're occurring after the coil/plug service this could mean a more serious problem - misfires are a precursor of cylinder bore scoring and it usual occurs on bank#2 on these cars. Take it to a shop and ask them to check it out and possibly bore scope bank#2. Regardless of what you do, I wouldn't take back to that dealership, they should have been able to give a more accurate diagnosis for you.

Thanks for the feedback. I am going to take it to an independent shop next week recommended by a fellow Porsche enthusiast. In fairness the dealer did say they could try replacing stuff, but they didn't seem real confident in that being a good strategy. Plus I'd rather not spend a bunch of money trying random stuff hoping to find the root cause. It seems like the dealer just doesn't want to deal with it anymore.

Thanks.

While bore scoring is a possibility it is probably not that. You have to be careful. An exam may see vertical lines on the cylinder wall and this can be diagnosed as bore scoring but when the engine is torn down the lines are superficial and not real scoring. In the meantime the engine is torn down and an engine rebuild will proceed...

Since plugs and coils -- the usual culprits in misfires -- have been replaced one needs to look elsewhere.

Are there any pending codes along with the active codes?

What can cause misfires on one bank can be a MAF. Yes, I know this sounds implausible but I recall a Boxster owner facing single bank misfires and eventually he replaced the MAF and no more misfires. This was one time out of a number of these multiple misfires reports so this is about as likely as bore scoring.

Throwing a MAF at the behavior is still throwing parts but consider it.

Another cause of misfires all confined to one bank is something wrong with the VarioCam system. What can happen is a solenoid/actuator can fail (in some cases a solenoid bracket can crack). The cam timing doesn't occur when it should. The engine controller recognizes something is wrong from the O2 sensor readings. The controller adjusts fueling in an attempt to get the O2 readings it wants. It doesn't. More fuel adjustment until finally the adjustment has gone so far misfires occur.

When my 2002 Boxster's VarioCam solenoid/actuator failed I was observing short term fuel trims and the one bank's trim was all over the map. Mentioned this to the tech and it was he who told me this could lead to misfires. BTW, there was no active error code yet. Just a pending code that pointed to the VarioCam solenoid/actuator on the affected bank.

Another problem is the VarioCam low/high lift feature acts up. My 2002 didn't have this but my 2003 Turbo did. What can happen is one or more lifters do not switch to low lift after cold engine start. Misfires occur because too much air is being allowed into the cylinders for which one or both intake lifters fail to switch to low lift mode. Bank wide the failure may not be with individual lifters but could be a problem with the valving/solenoid (or whatever) controls this for that bank. In the factory manual (at least in my Turbo's manual) there is a pretty involved process to diagnose if the failure to switch to low lift operation is to blame for the misfires. If so, the factory recommends replacing all intake lifters on that bank the problem is "dirt".

Have to mention it but if the car sat a while mice could have been at the car. I have encountered several cars in the local Porsche dealer for what proved to be rodent damage. However, I would have to believe a Porsche tech would have spotted the signs. Still a careful check of the car, the engine wiring harness, needs to be made. At the same time look for rodent sign on top of the engine under the intake manifold. On top of the plastic under body panels is also a place where rodent trash collects.

Some dealers and I think this will become more common shy away from the older water cooled models. The dealers do not appear to be as "afraid" of the even older air-cooled models but the water cooled ones are more complex -- mainly in the engine controller/sensor department -- and unless one is willing to drop the car off with a blank check to fund the work to find and diagnose the problem -- the dealer will nudge both the older water cooled car and the owner out the door. This is what happened when I had my 2002 317K mile Boxster in for a CEL. One dealer tried 2 times to find and fix this. The dealer found some problems the 1st time and fixed these and the engine ran better but the CEL came back. The 2nd dealer had the car for around 30 days and the tech made a few diagnoses -- one was the AOS which was rather new but I know can fail at any time. The AOS was replaced but to the dealer's credit further testing found the CEL returned and the new AOS was remove and the old one reinstalled and I was not charged for this. After 30 days I picked up the car and paid the charge we have agreed to -- I can't recall how much now but it was just maybe $200 or in that ball park and told me if I wanted it to make another attempt to diagnose and fix this leave a blank check. The engine may have to be dropped even opened up and since the car had so many miles and needed (its first) clutch job I elected to not spend any more money on the car and sold it to another dealer who put it through auction as a roller.

At any rate, I'm not sure how an indy will fare. Guess you'll just have to find out.

I had the indie shop check the car out and they couldn't find anything wrong (said they drove it 3 separate times). I have also driven it several times since then without issue. The CEL might have been a fluke, only time will tell. If it happens again they said they would be happy to do some further testing. I'm about to change the oil as well, so that should potentially give some indication if it's bore scoring-related (oil consumption). On another note, after driving for a while and the car is warmed up, I noticed the dash volt meter reading seemed low (13.8V at startup, then drops to between 12.3V-12.7V), but perhaps that's within the permissible range. I typically leave the car plugged into a trickle charger, so I haven't noticed any battery issues. Also, the front left blinker also seems to be blinking twice as fast intermittently. The last two issues could be completely unrelated, but I thought they might be due to grounding/other potential issues.