AutoTap and Misfires

[ideutsch]

Well, I finally broke down and bought AutoTap. It just seems like the SES light never goes out and I'm tired of the dealer. So the code I get is P0420, catalyst system efficiency below threshold. So I clear the codes (there were three instances of that code) and go out for a small drive, having autotap record all sorts of stuff. Got to a straightaway and floored it. At WOT, when RPMS reached about 5600 I was getting 210 misfires in every cylinder. They started off small, but as the engine speed increased so did the misfires. However, no code was thrown. It seems to me that having that many misfires would be bad, but I don't feel any loss of power and there's no DTC being thrown.

I have the log file still if anybody wants to see it. Is this normal?

[jmihalchik98]

bad #4 o2 sensor and/or cat

[Camarorulz]

I was having misfires at high-rpm in 4th gear because of a bad catalytic converter. You may think that there is no performance drop off from misfires, but believe me there is. I didn't really notice the drop in performance until a stock-*** Civic beat me on the highway. :eek:

I'll bet it's your cat.

[jmihalchik98]

shanes cat went when he was on the juice and he cut .6 in the 1/4 by replacing the cat.

[ideutsch]

I guess I should have mentioned that this is a new cat, I've maybe had it for a month. Already had 2 GM cats go out on me in the past year, now onto an aftermarket one. I was thinking it's probably an O2 sensor, but autotap shows decent readings coming from all three.

[Turbo V6 Camaro]

5600 RPM/2 = 2800 /60 = each cyclender firing 46.6 times a second!!!! so 210 misfires over 1-2 min time frame would only be noticed on the dyno or at the track.

check: plugs, wires coil packs. and you O2 and your cat.

also most peoples ingtion modual starts going bad the get hig RPM misfires.

[malice10985]

I would check all compontents of the ignition system like viper04af said.

Once I had a spark wire shift while I was driving and it melted itself against the exhaust. That caused super misfires and an SES light.