OK, I have been having a problem lately with the car feeling like it's misfiring. It only does it above 3000 rpms regardless of how hard i'm in the throttle. It is intermittent, but is beginning to happen more and more often. Also, sometimes it will be very slight, and sometimes it will be very violent. I had some work done on the car, and they said they pulled rear o2 codes (blown rear cat... been like that for way longer than i've been having this problem) and an EGR code. I have a pretty good knowledge about LT1s, but I'm not sure if the EGR could cause this to happen. Any help would be appreciated.

 

Now it's doing it every time I get above 3000 rpms. I've asked a few friends, and they said it sounds like that could be it. Any other opinions?

 

Coil, coil WIRE, clogged cat
Check for those first.

JR

 

Normally, egr well cause problems at idle or just off idle, not at 3k.Ck plugs, wires, opti, icm and wiring, coil and coil wire.

 

The EGR can also cause surging at cruise, but your symptoms don't sound like that. If it is a "violent" occurence, it is probably spark related.

 

I thought about that, but it does do it occasionally at cruise, and I've had burned wires before. It feels nothing like that. Also, when it was spark related, it only did it when the engine heated up (plug wires), and now it will do it whenever it wants to. Tonight on my way home, I got on it, and it spat and sputtered all over the place. A minute later i got on it again, and it was strong all the way through. Then I got on it again, and it sputtered again. Clogged cat may explain it. I've been spitting out pieces of that cat for a year and a half now. Maybe it just got a piece too big to get rid of this time. I know it sounds crazy, but it's done this before, and i'll just find a good empty stretch of road and I guess it finds its way out my cutout.

 

It's most likely the cat. Since you know the cat is fragged and your problem is under high load and/or high RPM it definately points to the cat. I've been in a car with such a bad cat it couldn't even make it up a hill with your foot to the floor Sometimes they will go quickly so I would do something about it before it gets real bad.

Since we're all a bunch of great mechanics here I'm sure we'd all try to find the cause of the melted cat before simply bolting a new one on to have the same thing happen again It's typically an ignition problem or exhaust leak that overheats a cat to meltdown, although some cats just go bad.

Also keep in mind that those pieces of the catalyst brick like to get lodged in the muffler, depending on what type of muffler is on the car.

 

It's a flowmaster catback, but i never run my exhaust closed. Cutout is always open. Loud and obnoxious is the way to go!! The cat started to frag right after i got my cutout, so i think that had something to do with it. Anyway, here's an update. I believe it is the cat because writing my last post gave me an idea. Went to our local "deserted road" and did a couple of 145 mph bursts and a couple of 110ers, and the engine woke up. still sputters a little bit, but it's about 97% better right now. didn't want to push it too much more tonight. That's alot of work for an engine in 10 minutes time, so i'll go see if i can't blow more out tomorrow. That's what you call a shadetree mechanic boys!!!! Thanks for all the help. Z ya later.