6G Celicas Forums

I recently purchased a 96 st and thought I would run seafoam through it... took it up through the brake booster line. Of course it smoked like crazy, but was still smoking a few days later with a CEL on.

Took it to autozone, code P0302 #2 cylinder misfire. the plugs looked like they had a lot of grayish yellow deposits on them, #2 was significantly worse, so i replaced all the plugs with autolite double platinum and the car still has trouble accelerating... if i take off from a light it feels like i'm in third.

i also tried disconnecting the battery and resetting the afr (pull ecu hazard and efi fuses, idle for 10 mins) and still having problems. also checked all the plug wires, they look ok... I havent yet pulled off the dizzy cap.

Could it be the O2 sensor? but it didn't throw an O2 sensor code?? I suppose I could throw in the O2 sensors from my other celica, but my parts car is a 94 st obd-i and has a 1 wire front O2 sensor and my dd is a 96 st obd-ii cali-spec and has a 2 wire front O2 sensor. so idk if this will work. Haven't looked under the cars yet to take a look at the post cat sensors... if there are any?

I'm worried about my cat too cause of the misfiring. Any ideas?

I found this vac line just chillin... from the look of the vac diagram, it goes to the TVV, I put it back, cleared the code but the car still runs bad.

Anyone think this is the O2 sensor? Its the only thing I can think of... I might just replace it.

Seafoam loosens carbon deposits. If you used it comprehensively, it's entirely possible you fouled your plugs. Most people who run it on a regular basis either do it just before they do a tune-up, or swap in cheap plugs while they run the Seafoam through the system then swap back to their normal plugs.

If a cylinder isn't firing, it's generally either ignition or fuel. Damage to your catalytic converter is unlikely to produce misfire in only one cylinder, if at all. Have you checked to see that you have spark on cylinder 2? Tried swapping wires to see if the misfire moves with the wire?

Thanks for responding galcobar,

I replaced the plugs but it is still misfiring. I took them out to take a peek:

Here is the plug in the #4 cylinder... looks fine


Here is the plug in the #2 cylinder... its blacker, probably as a result from the misfiring, not the cause


I also pulled the #2 wire of my parts car and put in on my dd, same problem. I also removed the cap and rotor and inspected them. They are like new. I didnt try to switch the wires. Should I switch #2 and #4 for this?

Usually I warm the car up before I drive it, but yesterday I just hopped in and drove it. The acceleration was all there and it was running smooth, but once the car gets warm the #2 cyl misfires... at idle, at load, whatever. I took a vid of the O2 sensor voltage, you can see it go really low or go to 0 during a misfire. Could the O2 sensor be going bad? There is no O2 sensor code... or maybe the O2 sensor is just reacting to presence of gas in the exhaust stream and the problem is being caused by something else?

http://www.youtube.com/watch?v=ey484flhgvY

Lots of after-seafoam problems are O2 sensor related... I want to be more sure before I just go throwing parts at it.

Bump... trying to get this fixed early this week... might need to take it to a shop cause I really need a car to ship parts out.

Did anyone look at the video?

try swapping fuel injectors between cylinders, or is this only a no-spark issue in #2? hows the compression in #2?

Did 2 compression tests this morning:
150 - 150 - 147 - 149 (forgot to have WOT)
154 - 145 - 150 - 151 (WOT)

Also switched #2 and #3 wires, still misfiring, but i didnt drive it long enough to throw a code. I'll check spark when I have my mechanic friend help me this afternoon... we are also pulling the fuel rail and swapping the #2 injector on both cars.

compression is fine, that cylinder is fine mechanically. there is some fuel getting to the cylinder because the plug is blackening but you're not getting good or complete combustion for whatever reason, poor spark or a bad fuel injector. ohms check the injectors and make sure they all read about the same resistance. mechanically the injector can be clogged or stuck open and either of those will admit fuel but cause rough running. as for spark a cracked cap will cause this as well. from how the plug looks you probably have either a weak spark or too much fuel. its pretty dark which is rich.

I decided against pulling the fuel rail because I have to remove the upper intake plenum to get to the fuel rail bolts which means new gaskets, etc. I checked the resistance of the injector, its right on spec at 13.8. Unfortunately I cant continue to guess on this, i'm gonna have to bite the bullet and take it to a shop. Need this car at 100% ASAP because it isnt inspected in this state yet, and it wont pass with a CEL.