Misfire???

[motorhead584]

Hello all,

I have not posted here much but hope to contribute more in the near future. I have a 2002 Trans Am Firehawk Vert. Mods include texas speed 1 3/4" long tubes, texas speed catted y-pipe, SLP MAF, loudmouth 2 catback, Frost mail order tune (after the bolt-ons), vette wheels, MSD wires, spark plugs that are about 2 years old with 500 miles or so, UMI strut tower brace and subframe connectors, K&N filter, Baer rotors, Goodridge brakelnes/Hawk pads, B&M shifter, spec stage 2 clutch/spec steel fylwheel, pro-products 80mm throttle body, slp smooth bellows. The car sat for about a year, occasional starts and runs in the year. I pumped the old gas out, replaced the fuel filter, and used Heet/Seam foam water removers and lucas oil fuel treatment. The car is still misfiring I believe. The service engine soon light blinks on and off while driving and there is a rough idle after running for a few minutes. Reading the forums it seems it could be the O2 sensors which were installed new with the headers about 2 years ago. I installed the Densos. Any thoughts?

[35th-ANV-SS]

Misfires could be a lot of things. Have you gotten the codes read? If so, what were they? If not, Autozone will read them for free.

Aside from that, I'd start with the easy stuff first. Check to make sure all your plug wires are in good shape and snapped on properly. Check to make sure a gremlin didn't chew up a vacuum hose or that a vacuum hose hasn't dry rotted. Clean the MAF. You can check the fuel pressure to ensure you're getting proper fuel to the motor. Should read around 58psi.

[motorhead584]

I haven't had the codes read but will very soon. I cleaned the MAF and checked the plug wires/vacuum hoses. It seems to only throw a blinking light when driving which I've kept to a minimum since this occurred. Haven't checked the fuel pressure but will tomorrow. Thanks for the response.

[35th-ANV-SS]

Could also be a weak fuel pump or lazy O2's. Let us know about the codes and/or fuel pressure at the rail.

[pajeff02]

Subscribed. If you end up replacing the O2 senders, the Bosch P/N 13111 replacements are the way to go. The parts store will try to sell you 13444, so be ready for an argument. I would suspect something other than the senders, but only some diagnostic work is going to rule them out.

[jfl330]

You might want to pull one easy to get to plug from each side and see what it looks like. O2 sensors work a whole side at a time so one plug will give you good indication of the status.

The blinking SES light indicates random misfires. Check that al the plug wires are fully seated on both ends. Check for any vacuum leak downstream of the MAF. PCV hoses are known weakspots. Can you read O2 sensors with predator or similar? If you have a smartphone, you can get a bluetooth OBDII plugin and read everything on the phone, extremely useful. Especially the fuel trims.

Jon

[motorhead584]

So I finally had the code read. It was PO302 (general misfire). From doing forum searches I understand this is for cylinder #2. I removed the spark plug, looked fine. Next step I would guess is the fuel injector and/or coil pack. The thing that gets me is this only happened after the car was stored for about a year which would push me towards the injector. Good tip with the smartphone...

[SteveC]

I haven't had the codes read but will very soon. I cleaned the MAF and checked the plug wires/vacuum hoses. It seems to only throw a blinking light when driving which I've kept to a minimum since this occurred. Haven't checked the fuel pressure but will tomorrow. Thanks for the response.

Your engine is running in "limp mode" which means you basically have no timing, it is firing left bank/right bank.

[0rion]

swap that injector and see if the code follows it to another cylinder.....then you can do the same with the coil pack.