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P0303, P0306 codes - How concerned should I be?

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I searched for various permutations of the P030x misfire code, but didn't come up with any advice regarding the seriousness.

I have a 2003 996TT X50 that I drove up to Virginia for the 13 Hour race (unfortunately in an Integra, not in a Porsche :lol: ). After a blustery, rainy Saturday night, I packed up on Sunday morning and upon startup got a check engine light. Since it was not flashing (and I had no good options to have someone look at it) I drove cautiously back home to Atlanta and plugged in the Durametric. There was a misfire on cylinders 3 and 6.

I cleared the code and it has not yet reappeared. How concerned should I be? What could have caused a misfire on both "front" cylinders? I replaced plugs and coil packs about a month ago, but the car has probably 1,000 miles on it since then.

My car is always garaged, but not a garage queen since she is my daily driver (and occasional camping vehicle :D). Did the rain cause the misfire?

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You are having misfires in cylinder 3 and cylinder 6. Check the electrical connectors, coil packs, and spark plugs in that order.

Because it happened in the rain - my guess would be bad connections or cracked coil packs.

Thanks, Loren. I was very gentle installing the new plugs and packs last month and the "3" and "6" coil pack connectors were the easiest to click on the packs. I don't really want to tear everything back apart, but I don't know if I am being foolish clearing the code and waiting for it to reappear - or hopefully not reappear!

Might this be a one-time fluke? Am I taking a risk waiting for the code to reappear?



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  • 1 month later...

Interesting! I just drove 350 miles in hard rain, had the car parked in it for a few hours, and also got P0303 and P0306 (same cylinders). I have 60500 miles and plan on doing my own service this Christmas break. I went ahead and ordered the coil packs to change them out while I'm down there doing the plugs.


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  • 2 months later...

You guys have any changes since these posts? Any re-occurrence? Same thing happened to me yesterday. Drove a bit, parked, had heavy rain... when I got back in the car and started it up, I got the check engine light and it's cylinders 3 & 6 misfiring. I noticed no signs when I started it up, drove just like it should. Planning on clearing the codes and seeing what happens, but I guess it may be the coils. Plugs are new, dealer had the engine out for some trans work a few months ago and changes the plugs then.

Could they have done anything? I don't want to bring it back there again. Paid WAY too much and the only reason I brought it there was that I expected the work I had done be paid by warrantly, but they denied it. No longer on warranty now.



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  • 2 weeks later...

Since I had filled up the day before, my thought was that mine was either cause by a bad fill-up, water getting in the fuel, or crud build-up on my injectors. So, once empty, I filled up with a bottle of techron and gas and went WOT as much as possible over the last week and I've had no problems. Hopefully I blew whatever it was out of there. Been running great.

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You guys have any changes since these posts? Any re-occurrence? Same thing happened to me yesterday. Drove a bit, parked, had heavy rain... when I got back in the car and started it up, I got the check engine light and it's cylinders 3 & 6 misfiring.

Ben -

I haven't had any more codes, but the heaviest precip I have driven through recently has been snow. eek.gif Seems like a one-off occurrence.

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