As you may remember I was getting an intermittent CEL P0420 (catalyst system efficiency below threshold) code. Cleaned MAF, cleaned throttle body, changed plugs and coils. The code disappeared and I thought I nailed it.

Yeah right! Now the game changed! This morning (2 months and 2K miles later) I've got P0300, P0306 and P0303 (multiple cylinder misfire code). CEL just lit up - not flashing. I've cleared the code and all good again.

Engine runs perfectly, no stuttering or irregular idle. Should I ignore or do you guys have any troubleshooting ideas?

My petrol was on nearly empty and the car was sitting about for two weeks. I will eliminate bad fuel first. I will refill and use injector cleaner albeit I doubt this will be it!

Any ideas are welcome...

Thanks guys.

 

For P0420 (or P0430) Porsche guidelines say if there are any O2 sensor aging codes to replace the indicated sensors and clear the codes and road test the car. If the P0420 (P0430) code comes back to replace the indicated converter.

My 2003 Turbo has never manifested a P420/P0430 error code. My memory of these codes was fortified by my experience with Boxster which generated a P0430 off and on for a couple of years. I finally bought a couple of rattle free converters from a salvage shop and had them installed in place of the original converters. P0430 gone. The problem was the bad converter had a loose brick. One could hear it knocking about at cold engine start or buzzing when up to temperature.

However, my 2003 Turbo has been generating P0303, P0306 and P0300 error codes upon cold start as often as every couple of cold starts. Warmer overnight temperatures reduced this frequency some.

Around 140K miles I replaced the coils and plugs -- the O2 sensors are rather fresh having been replaced at 132K miles. While the engine perked up some from the fresh coils and plugs (and likewise from the fresh O2 sensors) the misfires have not gone away.

The tech believes the problem to be a couple of sticky injectors.

I tried first Swepco fuel system cleaner -- the tech gave me a bottle -- then followed this with a bottle of Techron then another bottle.

The misfires still happen. The engine never misfires at any other time I might add.

You can try a fuel system/engine deposit cleaner. The best is Techron. Get a bottle -- which I think treats 20 gallons -- and add it to the fuel tank then fill up the fuel tank to help mix the stuff up.

Drive the car normally. The general rule is if you notice any improvement in the engine to run a 2nd bottle when the fuel tank level gets down to say 1/4 tank. I didn't really notice any improvement after one bottle but ran a 2nd bottle anyway.

I might add before and after Techron I had switched to using Chevron gasoline and while my Boxster engine perked up after a couple of tanks of Chevron gasoline the Turbo engine did not.

Anyhow, after the Techron it is advisable to change the oil/filter. The Techron can increase oil contamination and the last thing these engines need is more oil contamination.

Might add that what I have done to prevent the misfire errors from happening is to forego my usual let the cold engine idle until the secondary air injection pump shuts off and the engine RPMs drop.

What do now after a cold Turbo engine start is to as soon as the engine is running solidly albeit at an elevated RPM (~1K) after cold engine start to gently back the car out of the parking space and gently drive the car until the engine is warmed up. This keeps the misfires at bay but why I'm not sure.

In the meantime I continue to run Chevron gasoline in the Turbo and next service when I take the car in I'll ask the tech what is the next step.

 

Thanks mate. It seems we have an identical problem!

What about cleaning the injectors mechanically? Feasible? Or do they need to be replaced? I presume big job big $?

 

Never had to clean injectors. I recall coming upon articles that cover injector cleaning. The injectors are removed and put into a cleaning cabinet and cleaner is forced through the injectors and one can observe the injector spray pattern. Initially the pattern is not very fine and not symmetrical but as the cleaner works the pattern gets finer and the pattern much more symmetrical. The transformation is rather remarkable.

Primarily the problem is at the tip. When the engine is shut off some fuel can leak out around the injector tip and then dry and leave deposits. If one doesn't use a high detergent gasoline and compounds this with short trips over time this process can result in a build up of deposits to where it interferes with the injector's spray pattern.

Trouble is for the Turbos the injectors are hard to get at. When I talked to my tech about the possibility of the two injectors having marginal connections and maybe it was worth it to disconnect and connect them to eliminate any surface corrosion he was not very enthusiastic about this idea due to the tight fit of everything and the injectors and their connectors being hard to get at. I believe in order to get at the injectors the intake might have come out or possibly the engine will need to be dropped.

Have not yet had the opportunity to discuss this with the tech in depth.

You can clean the injectors in place. Use Techron. If the injectors are dirty (have deposits) this will clean the injectors, remove the deposits.

If the misfires go away after one -- and I'd just plan in using two bottles, two separate treatments -- of Techron that's a win for you.

If not then injector replacement is probably going to be the next step. I don't recall the mileage of your car but probably you would want to replace all 6 not just the 2 currently suspected of causing misfires.

I know with 147K miles on my 2003 Turbo if when I take the car in for its 150K mile service and if the tech believes injector replacement is necessary then I'll have all 6 replaced.

No way I'm going to have just 2 replaced and then in a few months (or less time) when one or more other cylinders misfire for the same reason replacing one or more injectors and doing this again and again until all 6 are replaced.

If 2 need to be replaced all 6 will be replaced.

 

Thanks mate. Might do the same.