(car is a 97 m6 Z28 w/ 69k miles) I've been trying to figure this out for sometime now and have just about had it. The deal is under partial throttle, response is great and car feels strong all the way up. Now, under full throttle in 2nd gear and up the car goes in and out of power between 4k to 5k rpm. It will studder to different degrees between this rpm range. Heres the kicker, it does'nt always do it. There are days when the car runs real strong, but the majority of time it falls on its face under full throttle between that rpm range. Another thing to note is it will also stumble sometimes in 5th and 6th at the 2k rpm range when given heavy throttle (i.e: passing on the highway), mainly in 6th though.

Ok, what I've done so far... I put in a new opti and prior to that I changed the spark plugs a couple months earlier. Changed the fuel filter. The plug wires are somewhat new, I did look at them in the dark with motor running too see if I had any light shows and didn't see anything. Check fuel pressure regulator and it was fine. Changed coil also.

The one thing I'm wondering is, could bad o2's give my symptoms? I did do the SeaFoam treatment about a month prior to all this and I've heard it can mess up the o2's?

Any help is greatly appreciated. If I can't easily figure it out soon do any of you know of a good shop in Southern California?

 

I have been having the same problem. I am putting in new plugs today and am gonna check all my wires cause I am pretty sure one is burnt.

 

But if it were plugs or wires, wouldn't that cause a problem ALL the time?

 

mine is weird. sometimes it's terrible and sometimes not so bad. I had really cold plugs in there for when I had the bottle on it and everyone I have pulled out has been extremely black. I think mine may just be a bad miss. If I get the plugs finished today and the wires all worked out I will be able to tell for sure.

 

I would re-check all the plug boots at the opti to make sure that they are seated nice and tight.
Check the coil and make sure it is grouded good.

 

Any thoughts on the o2's?

 

At the risk of sounding like a weeney, why in the hell do my posts regarding this topic never get any solid help???

How bout this then, any good mechanics in So Cal?

 

first thing to ask is what are the mods on the car?

it could be misaligned rrs, bad or wet opti (could dry if vented), plugs, wires, coil.... not sure why wires/coil would go out at 4-5k tho, check vaccuum tubes on the opti, they could come loose easily.

if thats what you wanted to hear

 

Only engine type mods are K&N cold air intake and cat back exhaust. Its a 97 so it has a vented opti, and I had the problem before and after putting in the new opti.

 

Check the cat. At wot, I don't think the 02s are being used as your car goes off of set tables, so you can rule those out.

 

I hooked up a Snap On Scanner to my car today and drove around. like 6,000 misfires within minutes and they are all on the drivers side. Opti? Injectors? what does everyone think.

 

it could very well be the injectors go ahead and check them then take them off and take them to some place that has that machine that will clean them. I did that on mine (at school for free!) it didn't fix my loss of hp problem but it certaintly didn't hurt it! It also shows you how they're fireing in relation to each other.

 

im guessing it could be your fuel pump,but like others have said,the sensors arent "on" at wide open throttle,so it most likely isnt any of the sensors,except for maybe the knock sensor(s),it could be pulling timingbut i doubt it.Ill list the things it COULD be:

Fuel pump,injectors,Optispark,coil, bad wires,plugs (doubtful),knock sensors (doubtful), or maybe just a vaccum leak (doubtful) .

Maybe you should try parkin in a dark parkin lot (preferrably not in a bad part of town ) and look under the hood and rev the engine up and SEE if any of the wires are arching. If you see any sparks or lights then its DEFINATELY an ignition problem. If you see any armed hooded suspicious looking people walkin up to you its DEFINATELY a mugging problem.

 

i've been to only one mechanics in socal. His name is Don Lorenzent(if i'd spelled corectly) he is close to disneyland at anaheim city..
here's his email: dynodonl@yahoo.com
he is specialist in 3rd gen camaros.. BUT my friend once rebuilt his tranny(a 94 Z28) with Don.. and it all went good.. i've had him fixed some problems with my car too.

 

Thanks guys, nice to see some responces.

MauriSSio- I already tried that in my garage at night and all looked fine.

TMD95z28- thanks for the shop idea, I'll check him out if I can't get this figured soon.

I'm thinking it may be fuel related, just was hoping someone may have the exact same symptoms and could tell me exactly where to look.