Have you tried to go with a colder plug and a smaller gap in them? I really think this is the problem that many of us had (have) when we experienced the cutting out. The only other thing i think that helped was the MDS box but i would try the plugs and gap first. I haven't had any cut out in a while now. Man this thing pulls hard all the way to 6500RPM.

Later,
Sean and Sherry Morley
Kansas Chapter Rep - Welcome to the VMOA!
Member Number #1479
Our Website - Morley's MuscleCars and MuscleBikes - http://www.fbody.com/members/one2dma...Musclecars.htm

 

get this:
I am a machinist,we build molds for a direct supplier for gm,
i have a 95 z28 rag top and i have the problem at about 4600 rpm it sounds like there is an ak47 going off under the hood,only on the drivers side,well the president of the supplier we supply for used to race the z28 back in 95 and he said,it may be a head gasket or the head itself may be warped,i have changed out the optispark twice and it still does the same thing,the optispark is a sealed unit except by the head where apparently coolant can enter and what happens is the coolant doesnt mix well with the optispark causing the explosion's you hear under the hood,i mean from 600 rpm to 4600 rpm my car rocks and rolls as soon as it hits that rpm BOOM ABNG BOOM,IT'S LIKE I AM EMBARRESED TO DRIVE IT,BUT THIS MAY BE THE CAUSE,YOU'LL HAVE TO DO COMPRESSION TEST ON THE COOLANT,FUEL,AND OTHER'S TO FIND THE EXACT PROBLEM,but he says thats probably your issue as well as mine?i noticed some recalls and was wondering if someone could help me decpher them.
1st-dec 98- 87-65-27
2nd-july 98- 83-15-12
3rd-june 96- 631514a
4th-may 96- 676117a

with the problem above the dealership diagnosed the problem as a optispark,but again i have switched it out twice and its still ****,so,i am leaning toward head gasket or a warped head,it may be able to be machined or you may need new heads,which if thats the case i suggest lingefelter heads to gain another 500rpm to help out in the ponies department!!!!

 

I would seriously try replacing the spark plugs with at least one heat range colder and then closing the gap up on them some. You may find out that this fixes the problem. Worst case your out $20 and some time. A heck of a lot better than doing a head gasket (which i don't think it is).

We had a problem similar to what you are describing when the car was completly stock and it was one of the wires going into the optispark was nearly burnt through (or a plug wires was nearly burnt through). I'm not a 100% sure what it was as it was fixed under warranty.

We did have a cat collapse which restricted the car and even made it stop running. I don't think that is the problem with yours but something to look at as well.

Later,
Sean Morley

 

thanks Sean,

I will give it a try,you know as much as any with these z's that they arent fun too work on,but i will definetly look into it.and i will save the thread to let you know the final result as a ye or ney...by the way, i am selling it,if you know anyone who may be interested,i am asking the payoff amount,the warranty company dumped me after they put 5600.00 into it last year,i have all the reciepts,then i put new rotors and ceramics at all four corners. anyhow i am a beleiver in advertising,it works,thanks for your help,,Dano

 

I have read all 20 pages of this
why........
cuz my turd is doing the same thing
i have all these mods so i never noticed it until i got a wide open space at 3 in the mornin

Alot of you guys say your wires and plugs were the culprit
but me....i am the proud owner of a delteq coil pack system
i will never change the opti again..GM should pay me for ever seeing that stupid invention. All of us have adjusted our own valve lash
I really think that is the problem and ive already played with them 6x
Where do you purchase the hydrarev kits and are they really worh it
My dyno run says i break up at 4700 and really bad
Vibrations are worse than a mack truck but only after it breaks up
still put out 315hp at 4500 on the dyno tho

 

i read through this whole thing myself, 2 years and cant seem to get a legit answer.

my datalogs are normal, but every gear, ~5200rpm, feels like im hitting a 2 step. cause i know my redline is 6k.

just did all my plugs (TR6 @ .029), i have 1 burnt wire i am about to replace, and am putting in a msd blaster coil this weekend. if that doesnt resolve my problem im not sure what to do, as i think my spark is getting "blown out" from the boost on the stock ignition. probably check the valve lash next, but the way the car acts, it does feel like floating valves..it feels like an actual rev limiter, as i tried to push past it once.

 

compression test!

 

I had the same problem,
First time I tried to fix it, I changed the plugs and wires including the wire from the coil to the Opti. Problem fixed.
After six months it started again, this time I bought a scantool and I got strange results on my IAT sensor, it was showing 155F when the outside air was 40, so I pulled it out and tested it, it came out just fine, I checked the voltage on the connector and it was fine as well (5V)
So I decided to just disconnect the IAT sensor, guess what.....car pulls great, no more miss/hesitation/stutter.

 

well, ran new wires, and bought an msd blastercoil off a friend, and it is pullin to 6k like a champ.

just an opinion of mine, the 93's have no maf, the MAP and IAT are much more important to us than the 94-97 guys. if everything was working correctly with the sensor, it wouldnt read 155F. but if it was broken it would read like 300 something, or negative 33 if its touching...or the other way around, i dont remember exactly.

 

Had the same stumble problem many of you guys mention... was bumming me out.

Posted a separate thread about a month ago when I couldn't find the right "key words" to search for.

Found this thread, and light bulbs went off.

Anyway, I was pretty sure that it was a bad coil wire based on the fact that everything was running great until the coil wire fell off 2X while driving... Noticed car would stumble (ak47 on driver's side) at ~5000 rpm..

Car wouldn't start the other day. Got around to it today... new coil wire (didn't do the other 8 plug wires yet... don't have the stones for that job right now)...

Car is BACK... pulled like a freight train up to 6000...

I appreciate everyone's input on the site.

JT

 

I've been fighting with ignition problems for almost the entire time i've owned this car. Bought a Delteq thinking it would give me a nice performance gain and help alleviate some of the ignition problems associated with LT1's .... boy was i wrong. Car starts and misses at idle... misses on rev, just misses everywhere. I've tried replacing the optispark, spark plugs and plug wires... still doesn't work. This is all leading me to believe that when i get this misfire figured out (if i ever do) i should get a LS1 z28 instead.....


My advice: if you want to mod your LT1 (or even LS1 im sure) wait, save up a LOT of money and just do it all at once - rip the motor out of the engine bay while you're at it. Get ceramic coated headers and wrap them, seal up every piece of harness you can and just keep it as sealed up as possible. Remove the A/C and all of its components, relocate the battery to the back if you can and yank ALL of the emissions crap out of there - just free up as much room in that engine bay as you can, you'll thank yourself for it! Point being, just save up and do it all at once with someone who is KNOWLEDGEABLE and has done all this before....

 

problem with doing it all at once, if something was to arise, where the hell would you begin to look?

 

I ended up selling my car, with the miss. I am guessing that it was the opti seal, as it was leaking a little bit of oil around the opti. That is my best guess as to what happened. The buyer is a friend of mine so he will be installing a new opti and seal this weekend. I will post back if that solves it.

Good luck to all........

 

So while I can't tell you what specifically was wrong (as there were many questionable areas) I can tell you what was done to fix the car. Car now runs excellent with no more miss.

1) There was an oil leak somewhere that actually caused the opti to have oil inside of it. How, I don't know, but when they swapped in the new one they said the old one had oil in it.

2) The 3 bolts holding the cam (?) in place (this is what they said, though it could have been the timing chain maybe) were screwed up, as in 2 were finger tight and stripped and one had the head of it fall off just by looking at it. They said the cam was probably moving around in there or something, hence screwing up the timing and such. I am unclear exactly what happened as I never was in that area but something seriously was messed up according to them. I would bet that this was the cause.........

Hope this is all helpful!

Brian

 

Car is fixed, miss is gone. Seems like it was those 3 bolts that were the problem. They drilled and tapped them and put 3 new ones in and it is all better. If you are plum out of ideas maybe you should take a peek at those bolts, since apparently they can just got to hell as nobody had ever been down there before.