Misfires and flashing CEL - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Hello, this is my first time posting on the forum. i’ve had my boxster (03 S) for about 10 months and i’ve done a lot of maintenance and work on it. it’s been driving really well and hasn’t given me any major issues until today. My tank was just about empty with the fuel light on, so i stopped and filled my tank. i only ever use 93. i pulled out of the gas station and got it up to about 6k until it lost power and had a big backfire out of the exhaust. the car had been up to operating temperature for a good 30 minutes, and i had only stopped for maybe 5 minutes to refuel. i had to have the car towed and it runs awfully. I had 3 codes show, random misfire, misfire on cylinder 2 and misfire on cylinder 1. i disconnected the coil packs on cylinders one, and then two. each time i fired the car up it sounded the same. i replaced the plugs and no change. coil packs were replaced in august, they’re still in excellent condition. since i’ve owned the car i have done the IMS and chain tensioners so i don’t see how that could be an issue. But then again the sound reminds me of when a spark plug popped out of the head on my old vw bug. I’m usually good at diagnosing issues on this car but this time i’m truly stumped and i’d greatly appreciate any feedback or input.

Try clearing the codes and seeing if they come back. Is the place you got gas from a usual location/brand you usually get it from? just to be sure it's good to post the actual codes set and any pending codes. It sounds like you were getting p0300, p0301 & p0302 but the actual codes help verify it isn't anything else.

Usual place yes. Cleared them and reset the ecu, came back instantly. It stopped flashing though. codes are p0300, p0301, p0302, p0303. seems like the issue is isolated to bank one. really hoping it’s not something major. i might try swapping the bank one and two coil packs and seeing what happens. as the motor cooled down it got more and more difficult to start. i’d have to crank it a bit and it would sort of chug. lots of vibrations.

when mine did that I had a chewed fuel injector wire,..Frank

easy thing would be to swap coil from cylinder 1 to anything on bank 2. clear the codes and see if it follows. If not then you know plugs & coils are good. Next would be wiring. Do you have a durametric? You could watch the number of misfires on each cylinder. I would let it cool down overnight and then in the morning clear the codes, then start the engine. Does it run bad for the first 2-3 minutes or does it run good and then after 2-3 minutes run bad?

http://986forum.com/forums/boxster-general-discussions/28644-1998-boxster-p0301-p0303-odb-2-reading.html I hope you are not having the same problem described in this post.

i suppose fortunately that doesn’t describe exactly what’s going on. the car cooled down all the way to where the SAI pump kicked on like it does on a cold start and it ran equally like garbage. going to swap coil packs, check vacuum leaks and then move onto wiring. seems like a fun weekend ahead!

I would say you're either getting to much air or too little fuel to bank 1. Check vacuum leaks. If not that, then it's likely a fueling issue. Gas.near.me has been particularly ****************ty since the shortage, even 93 octane. Try running a bottle of techron or seafoam. If that doesn't fix it, I would consider replacing the fuel filter and then the injectors. Sent from my POCOPHONE F1 using Tapatalk

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I’m around atlanta so we got hit with a shortage too. Checked for vacuum leaks, didn’t find any. ran the engine while spraying starter fluid inside the hole for the valve on the intake boot and the rpms increased but it didn’t smooth out at all. i’m wondering if the noise it makes is a dead injector? at idle it’s quiet, but when you open the throttle at all it’s a bad clunk clunk. I can attach a video if it would be more helpful

The occurrence of a backfire after filling with gas points to an open purge solenoid that allowed gas to enter your intake. The backfire could have damaged your intake or its gaskets, leading to vacuum leaks. Sorry, I am not familiar with the evap systems in Boxsters, this is just general automotive advice. I would smoke test the intake. Sent from my SM-G781W using Tapatalk

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I do have an occasional howling by the fuel tank, which to my understanding is where that solenoid would be located. i’ll see if i can get my hands on a smoker for the intake. maybe it failed all together and there’s some kind of vapor lock? i know this is a completely different animal but i’ve had it happen on my old vws

my bank two primary o2 only reads about .04 volts and doesn’t change. the bank one sensor works properly with fluctuating values. I don’t know if this has anything to do with it. I replaced all o2s in december.

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I wish i had a durametric. It’s been on my shopping list for a while, but i was about to do a full suspension refresh. I might have found something as my bank two o2 sensor is reading nothing, but confirmed it was working by swapping it with bank one. seems like that might be the dead cylinder, but the why is now the big scary question. bank one gets a normal o2 reading, but yet that’s the side i’m getting misfire codes for. I’m still stumped. Pulled all the injectors and verified they’re all working and resistance tested them, they all seemed okay, except cylinder one injector smelled like burnt electronics.... and had the most visible deposits on it. i’ve already ordered a new set.

Here is the link to the video of my engine. any thoughts would be greatly appreciated https://youtube.com/shorts/TdszKNnrBtM?feature=share

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If bank 2 O2 Sensor gave no signal in bank 2 but it did when you switched it to bank 1 then the sensor works. So you have a wiring problem on bank 2 O2 sensor wiring. Sounds like you have multiple issues. What cylinder are you saying is dead.??? And why do you think it is dead???? Did you get a code for the bank 2 O2 sensor not working???

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I have aftermarket headers, and the o2 attaches onto the pipe coming off cylinder 6. i have no o2 codes. I think the cylinder is dead because there is no signal coming off that sensor even after i’ve verified it works. so if there is no combustion happening it would read close to .0v like it is? I pulled cam plugs and verified that the can timing isn’t out since everything lined up with my locking tools from the ims kit. I’m going to try and see if it is a wiring issue with the o2 circuit, but i dont see how it would just fail out of the blue, but anything is possible i guess. I tried attaching a link to a video i posted on youtube showing how the car sounds and runs but i don’t think it let me post it

Get an eye dropper full of water and drip a couple of drops on the header tube for the cylinder you think is dead while the engine is warm and running; if the cylinder is dead, the water will just sit there, if it is working, it will flash off as steam.

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I’ll give it a shot when i get the injectors back in and fire it up again. any tips on double checking the wiring? I did continuity test on all injector plugs to rule out a short, resistance tested coils and they were all .9ohm. they’re recently new beru packs.

Curious why you think it's the injectors. From reading it looks like you have at least a wiring issue with the o2 sensor. What sensor on the cylinder are you referring to? do what JFP suggests. Very much doubt you have a bad cylinder as you would have more problems and noises if so. To test the injectors the best thing to use is a NOID. It will tell you if an injector is getting power. You can also bench test each injector to see if they at least work, which I bet they all do.

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Those O2 sensors should be 4 wire sensors. On a 4 wire look for two wires of the same color they are the heater circuit. They should show 12v with key on. Of the other two one is ground. The other one is the signal wire back to the DME/ECU Hope that helps. I have gone back and re- read your posts in this thread. In post #12 you stated that the O2 sensor voltage was .04 In post #13 you state it is reading nothing. In post # 15 you state there is no signal but the voltage is close to .0v Seems that the bank 2 sensor is working. These O2 sensors work in a very very narrow range. You stated you have not gotten any O2 sensor codes so my guess (after re reading your posts) is that the wiring is fine. You could back prob the harness to sensor connection from the sensor side of the connection and check the two wires that are the same color. you should get 12v or near battery voltage with key on. If that circuit (heater circuit) is good I would bet that the wiring is good. But that Cyl. may be dead as you stated. If you think you have a dead Cyl. you can check it with a compression gauge. Or use a vacuum gauge hooked up to the intake. The needle will tick every time the dead cyl. comes up on the compression stroke. Compression gauge will be easier if your not familiar with reading vacuum gauge needle action. Or as JFP stated water on the exhaust for that cyl.