Misfire at high load/rpm

[GinsuGuy585]

For some reason cylinder one was misfiring last night while I was doing some heavy pulls. The freeze frame info:
Load - 87%
Intake temp - 68F
TPS - WOT
RPM - 5067
Fuel trim - 100.87%
Speed - 87.5mph
It also said it was running open loop, which I assume is normal when you mash on the pedal.

I just did the Sea Foam treatment (thats why I was running it hard) but I have had this problem at high rpm/high load before; always on cylinder one. I'm thinking it's plug/wire related, but if anyone has had this issue before please chyme in. This only happens when I get to 5k rpm.

Also I threw a 420 - Cat low efficency (normal, sim will be in soon) and a 137? (can't remember) the obd2 reader said the MAP sensor had low frequency. I'm wondering if that could be because of the sea foam or the cold weather and hard driving. Likewise if you have had this before speak up.

[97rs4life]

Re: Misfire at high load/rpm

is your cat. conv. a hi-flo aftermarket one or stock one yet?

how old are your o2 sensors?

how many miles, what year car, mods, etc?

[GinsuGuy585]

Re: Misfire at high load/rpm

Stock cat, I'm going to hollow it out asap (weather permitting). No idea about the o2 sensors, but the front one is fine. I'm betting the cat is just dead or already hollow. Car has 106K on it, probably driven hard most of it's life, but I've added engine cleaner to the gas every 5th tank since I got it a month and a half ago and it runs fine.

Exhaust (after cat) was a custom job put on by the previous owner. It looks like whoever did it cannibalized a flowmaster catback. It has the resonator box, but no muffler, and from there a Y-pipe to dual pipes (where the muffler should be.) It sounds better than other blowmasters I've heard so I'm not complaining.

I'm getting an oil change tonight or tomorrow, and doing a plug/wire change right after that.

[tkoforpresident]

Re: Misfire at high load/rpm

what year car?

[GinsuGuy585]

Re: Misfire at high load/rpm

1997 base model.

[GinsuGuy585]

Re: Misfire at high load/rpm

So I'm going to run it gently just so it will run all of it's internal tests, then get an inspection before the low cat efficiency code pops. They only plug into your obd2 and make sure it's not throwing codes, no sniffers, no questions. :)

[CoasterKev06]

Re: Misfire at high load/rpm

I had the exact same happen to me... however I didn't throw a cat code. My purge solenoid through one. My SES light started flashing at me and throttle response sucked for about 5 minutes...

My guess is that it's a plug problem since my wires are practically brand new (< 1 year old) taylor spiro pros...

[GinsuGuy585]

Re: Misfire at high load/rpm

I forgot to mention that, but the SES light did flash for a bit. I didn't notice a big change in throttle response.