Random Misfire issue

[GripGirl]

Hello everyone, I've had my 2003 Boxster S for just a little over a month. Picked it up from the original owner 3.5 hours away from my area who had extensive maintenance records from an aftermarket Porsche specialist shop.

Car has 60k miles. Owner has receipt for 60k mile service done earlier this year.

Shortly after daily driving the car, check engine light comes on. Codes are: P0300, P0301, P0302, P0304, P0305 (random misfire in cylinders 1, 2, 4, 5).

Took it to the Porsche dealership, who diagnosed it as needing coils. We brought the car home and my husband (a mechanic) replaced all the coils using parts from Pelican, and he cleared the CEL.

Check engine light came back on 4 days later. Same codes for the same cylinders.
I don't feel like bringing it back into the dealership and paying yet another $170 for a bad diagnosis.

I'd appreciate any insight as to things we should be checking. MAF? Vacuum leak? Wires? Voodoo hex?

[Brando]

Check the connectors and replace the plugs as well. My 2006 Cayman threw a misfire code literally 1 day into ownership (by me). A new set of plugs and coil # 1 fixed it. Mechanic also cleaned up the connections.

[GripGirl]

Plugs were replaced earlier this year at the 60k mile service, so I'm not sure that's it. I'm not opposed to checking but I'm not hopeful about that fixing it.

I just find it odd that it is a misfire in cylinders 1, 2, 4, and 5. If I understand correctly, those are the two front cylinders on either side of the motor. (Why not the back one?) Is there another cause -- fuel rail maybe?

I JUST got rid of a problematic car that I threw way too much money at in guessing what was wrong with it. I don't want to have to go through that again.

[BYprodriver]

$170 should entitle you to something of similar value! I would return there & allow them a 2nd chance at no cost to you. My 2000 Box S has 102K miles & original coils although admittedly a easy gig here in So. CA

[steveng1993]

I too once had a car with a wicked misfire problem that I too to an indy which then promptly said it was the coils, pay me for an hour please. I bought 6 new coils and it wasn't the problem. Exactly as you. In this car's (bmw e36) case it was the ecu that took a dump. I don't think that in either case yours or mine the shop did a real diagnosis, they just took a look, yep, the coils. From all the hundreds of posts I have read online never have I heard of a coil misfire causing problems on more then 1 or 2 cyl.

In your case there can be a few causes that I can think of, my first suspicion would be a vac leak issue. I recently had a problem on my other bmw where I thought I would swap out fuel injectors. I ended up getting tons of misfire codes with the new injectors, old injectors back in corrected that problem.

If it was me in your case I would probably take it back to the dealer you had it at and insist they do a smoke test.

[bell]

Definitely sounds like a vacuum leak, that or the fuel pump is on it's way out......a smoke test will show any vacuum leaks as mentioned....

[GripGirl]

Thanks everyone. I'm trying to avoid taking it back to the dealer if I can. Their dealership is under construction and they are working from a much smaller space now, so it takes a week just to get in there.

Husband is going to hook it up to the smoke machine tomorrow at his shop and test for a leak. Wish us luck.

[paulv]

Originally Posted by GripGirl

Thanks everyone. I'm trying to avoid taking it back to the dealer if I can. Their dealership is under construction and they are working from a much smaller space now, so it takes a week just to get in there.

Husband is going to hook it up to the smoke machine tomorrow at his shop and test for a leak. Wish us luck.

GripGirl,

Have your husband read the freeze frame data from the CEL going on and post them here -- looking for rpm, vehicle speed, O2 readings, Fuel trim (short term and long term). Before testing stuff, try some diagnostics.

Regards,
paul...

[tomk]

causes of these kind of symptoms can very tough to nail down, especially via message boards

its easy to waste a lot of money and time i always do the easy and cheap things first, try a bottle of drygas, look for vacuum leaks, check the bulkhead connector to the FI harness, fuel filter but before you buy something expensive take it to the dealer if you are not sure
good luck