CEL - Codes P0204, P0300, P0304, P0306

Hi all, I'm relatively new to the forum and just got my first Porsche (996) 4 months ago. I am amazed at the wealth of information here. I was hoping for some guidance. I took the car out for a drive (nothing fast) after it sat for a couple weeks. Drove it to a restaurant with no problems. I started it up to leave and the car started shaking as if there was a mis-fire. I just get the codes from my Durametric and they are as follows: P0204 Porsche fault code 153 - Injector circuit cylinder 4 P0300 Porsche fault code 507 - Misfire detection (total) P0304 Porsche fault code 511 - Misfire cylinder 4 P0306 Porsche fault code 509 - Misfire cylinder 6 The car is a 2002 C2 with a VF Engineering Supercharger on it and 61K miles. I am guessing the plugs have not been changed since the SC went in ( I see no records of them being changed). I also noticed that the cylinder head heat shields are not there which I heard can accelerate the aging of the coils. I cannot find anything around the P0204 code for the injector circuit. I assume this means that the injector might be bad but not 100% sure. I work on my own cars so I have no problems doing much of the work myself (unless these codes require a professional). It's also fun to learn how your car ticks. I am not sure if fuel injector work is something I should get into or not. My thought is change the coils and plugs, reset the codes and see where things are at. Does anyone have any comments on whether I'm possibly on the right track here? Is there any other information you would want from me?

Additionally, the Check Engine Light was not flashing. It was solid.

If changing out the plugs and coils don't work look at the catalytic converter(s). I had misfires taking place on one bank and replaced everything to not avail. Then I found out the cat was failing so once I replaced it the misfires were gone.

Quotes source post: 9744589

P0204 is an OBD fuel and air metering related error code: Injector Circuit/Open - Cylinder 4; as per my reference. The P0300/P0304/P0306 are misfire codes. P0300 is multiple misfires. Since both cyl 4 and cyl 6 registered misfires, this explains P0300. What explains P0304? P0304 I think arises from the P0204 problem. That the CEL was not blinking suggests the misfire is a lean misfire and the open circuit error code on that same cylinder suggests the fuel injector is not working. I'm a bit leery of advising anyone to attempt fuel system work simply because of the very real risk of a fire. Whether a fuel injector -- # 4 cyl. -- has simply gone bad or there's a connector problem I can't say. Absent any work in that area the connector thus being undisturbed my money would be on the injector just being bad. While O2 sensors are relatively easy to swap from bank to bank swapping fuel injectors brings with it fire hazard or the risk one damages otherwise working injectors moving them from cylinder to cylinder or by flexing hoses/etc. introduces a fuel system leak. Up to you and your professional tech what you want to do. As for P0306 maybe you need to address P0204 first. It is only a WAG on my part but the rough running of the engine arising from the severity of the cyl. 4 misfire might be introducing a misfire condition at cyl 6. Oh yeah, the SC... Well, SC really takes a toll on plugs. But first, an aside: The SC requires no little HP to drive and thus if the SC adds say 75HP to the engine's output the engine might be making 125HP, the missing 50HP going to drive the SC. Thus the engine is boosted from say a base line of 300hp (I don't recall the factory output of your car's engine stock) to 425hp. This extra output takes its toll on plugs but requires perfectly functioning coils, too. Furthermore, more output means more heat and more heat means shorter lives for among other things O2 sensors. Might mention with more air being fed to the engine and assuming the fuel pressure remains stock to add the extra fuel the extra air requires the injectors are left on/open longer. This means they run hotter and this can only shorten their life. Thus, the injector of cyl. 4 might have reached the end of its life and the other injectors might not be far behind. Sincerely, Macster.

Thank you for such a thorough overview. I think given the fuel injector issue I am going to get it into the shop and not attempt to do this myself. I'll update and let you know what the results are.

I wanted to post an update to see if anyone has any additional thoughts. I pulled out the air intake pipes from the supercharger to get at the number 4 injector and simply made sure the electrical connection was pushed down. I then reinstalled the intake pipes. I took the car out this morning around the block and didn't feel the misfire. So I cleared the fault codes and drove it around the neighborhood (only around 30 mph). Car seems to be running fine right now with no feeling of a misfire. I drove it for about 5 - 10 minutes. I am not sure if I just didn't drive it enough or if I have some sporadic issue on my hands. I would think if the injector is bad, I would get a code right away right? Has anyone noticed if it is typical to have misfires come and go? I still plan on bringing it into the shop to get checked out but I like to be armed with some knowledge as I love learning about this car.

Quotes source post: 9752058

Ideally you want to do a follow up test drive driving the car like you were driving it when in your car's case the misfires occurred. The problem is after having a problem and attempting to fix it -- you may have fixed it -- the follow up test drive is tentative and doesn't really give the engine enough run time, under the varying running conditions, for the problems/symptoms to manifest themselves. The driver thinks what he did fixed the problem then during a longer drive the symptoms come back and the driver looks elsewhere when it was what he originally suspected but didn't fix right the first time. Or maybe he did fix the problem right the first time. To this I point out there are always 2 problems, unless there is just 1 or 3 or more problems. So, the fiddling -- intelligent fiddling -- with the wiring addressed one problem, but there's something else going on. Which brings me back to the SC thing... Fueling of any engine is very important and for a SC engine is even more important. This means as I touched upon earlier the injectors want to be in rosy health, but the fuel pump wants to be up to the task of being able to supply sufficient fuel to the injectors. My sole experience with a bad fuel pump is it just quit. But if a pump say gets weak as it gets hot it may not be able to deliver enough fuel and this can cause all sorts symptoms. Remember the engine is generating a lot more HP courtesy of the SC and the extra air it supplies. To do this the engine requires a lot more fuel. There's some margin in the fuel pump, how much fuel it can deliver, the fuel filter and lines, how much fuel they can flow without a problematic pressure drop, but this level of margin may vary and in your car's case the margin may be on the low side to begin with. A stock engine may not have ever been affected. But with the SC and the extra demands it places on the fuel system... Oh, that fuel filter. Since the engine is burning more gasoline the filter filters more fuel and fuel filter changes are based on miles with the assumption so many miles means so many gallons of fuel filtered. Well, the SC requires more fuel which throws this out the window. An inline filter can collect quite a load of trash and this works to affect fuel flow. Lastly, fuel pressure is critical. The DME expects fuel pressure to be within a narrow range and if under load the fuel pressure drops rather suddenly misfires can take place. (Might point out in the Turbo Porsche a fuel cooler is fitted -- chilled by the A/C system -- to help keep the fuel along with the pump in the tank cooler.) The DME will not log misfires -- at least lean misfires -- under low fuel level conditions. (My info -- source I can't recall now -- is if the low fuel level warning light is on this is what the DME goes by.) So, bottom line is you want to make sure the fueling system (and I think I mentioned the plugs/coils in an earlier post) want to be in tip top shape. But first treat the car to a longer test drive but be prepared at the first sign of trouble to back off even shut off the engine just in case there's something more serious going on. Sincerely, Macster.

I know it's been a while since I originally posted this issue so I figured I'd post an update. I have driven the car several times since the CEL and engine codes occurred. I have not been able to reproduce the problem. Good from that perspective, bad in that I have this hanging over my head now. At any rate, I've put her in storage for the winter and plan on have my local tech take another look once I pull it back out. When I think back to what I did after the CEL occurred. One thing I did was pull the air intake from the supercharger. I do remember the Blow-Off Valve was not secured tightly to the intake hose. I'm wondering if I fixed a vacuum leak when reassembling the intake pipes. Is it possible that a vacuum leak could cause a misfire and Injector Circuit/Open to occur? By the way, I never did post a picture of the car.

Sorry to Bump. Just wondering is anyone knew if it is it possible that a vacuum leak could cause a misfire and Injector Circuit/Open to occur? See post above.

A vacuum leak could cause a lean condition, which could definitely lead to a misfire.

Thanks for the reply, I appreciate it. Happy New Year All.

I have been scouring the internet to see if someone has been having the same issues as I have with my 997, and you my friend, are that person. Have you ever had any other issues with the car? Im getting the exact same error messages through my Durametric as you did, and Im going absolutely nuts trying to fix the problem. I, like you , am hesitant to go attacking fuel issues without good reason - so my next idea was to start pulling all the ducting to get some access to the injectors to check the wiring to them. Any info you can give me would be greatly appreciated. Thanks!

Unfortunately I don't have anything more to add. I had a loose intake hose connection from my supercharger blow off valve to the intake pipe. I fixed the connection and reset the codes. Haven't had the codes appear since.

Alright - I appreciate the help. At least I know that I could be having a vac issue that would cause that. thanks for replying back so fast.

I have the same codes and Zim in Texas diagnosed it as a loose injector harness plug on number four. I never unplugged this wire, but did unplug number five and found it truly difficult to get seated correctly. Also, the car has been shuddering when you come to a stop for several years now and that suddenly quit after number four injector connector was reseated properly. So go back and check to make sure that all your wiring harness connectors are seated completely. By the way that shuddering I mentioned was misdiagnosed as bad motor mounts.