Cylinder missfire p0303

[99FirebirdV6]

Hello all. This would be my first posting here. I will make the long story short. About one week ago i got a ses code P0303. Had it checked at the mechanincs and they said there was no problem. Just today the engine started acting really weired.. the engine is shaking like i am driving through speed bumps and throwing p0303 code all the time. i know its definately missfire. took it to the same mechanincs again.. they are telling me i need to change the spark plugs. My car has 70k mil. and i dont it the spark plugs were never changed. So I will get the spark plugs and the wires changed tomorrow. The labor fee they are asking is $178 to do that. How hard is it to change them... does anybody have any good instruction to do so.

Also what do you guys think about the problem... i know its definately missfire... the car has very rough idle now... and constantly shaking.

i kinda lost my trust on those mechanics coz they told me last week the spark plugs are fine and now they are saying go change the spark plugs.

thanks

[98Camaro3.8]

P0303 means cylinder 3 is misfiring. Plugs+wires would always be the first guess.

If you've never changed plugs/wires on a 4th gen V6 F-Body, it will be a huge pain in the *** to do it.

If you don't like that mechanic, try finding another shop to take it to.

[99FirebirdV6]

I forgot to mention.... the mechanic also told me that the last code it gave was for multiple misfire.

I also noticed that during idle the voltage meter goes down (and comes back up) and if the headlight is on it seems like its about to die.

Could it be the coils?

[98Camaro3.8]

Yes it could be the coils, but the most likely cause is always plugs+wires. Could be lots of other things too, but always start with the simple/common stuff. ;)

[97rs4life]

plugs and wires. I had a misfire awhile back on mine, was a bad wire so I replaced all the wires and plugs

[kinetic]

yeah, it's a pain in the *** (hands, really) to change the plugs, because of the positioning of them.

but personally, I'd change them myself, because parts are expensive as it is, and then there's labor...

just get the plugs, wires, and a 5/8" socket + 6" extension, and wrench, and do it yourself (one plug/wire at a time). the results will be more satisfying, especially knowing you did it yourself, IMHO.

[nda0602v6]

I had the same problem with the misfire plus I was getting another code (po420). I replaced the spark plugs with AC Platinums, replaced the air cleaner, the drivers side oxygen sensor and the fuel filter. I also switched to premium gas for a while too. Doing all that seemed to fix the missfire problem completely, no more po303 codes. I'm still getting a po420 code but I'm having the Cat replaced next week under wannarenty.

It took me about a 45-minutes to change the plugs and it was my first time doing them on an 4th gen F-body. My 3/8" swivel head wratchet really helped out.

[98goldbird]

I believe #3 is in the middle on the driver side. You could get to it, but the wire change is a PITA. What I would do is change the plug yourself, and if that doesn't fix the problem, then the wires are up to you. You could change them yourself or have someone else do it. Reason why they're charging so much is because #1-3 wires are clamped together to the firewall to avoid touching the pipes and fouling up. And that grommet that they're attached to is a PITA to take out or undo. I actually had to cut mine.

[99FirebirdV6]

problem fixed. it was actually a bad coil. the coil for cyl. 3 and 6 was bad. replaced and workes just fine.

man.. i almost paid more than 200 to get my spark plugs changed.

thanks guys.