95 Z28 LT1 Falls on its face at 5000rpms.
 

I'm new here and to owning a 4th gen F body Z28. I've owned a couple of older models but the newer ones have a whole list of problems I've never encountered. Mine is a 95 Lt1 as far as I know it is completely stock but in prestine condition except for the 120,000 miles it has on it. It uses no oil , doesnt smoke, and purrs like a kitten. However From a dead stop take off ( In pedal to the metal situations) at 5000 rpm it will stall (not quit) but start sputtering and popping like the engine spark has a governor on it. It does this prior to shifting to a higher gear. If I'm rolling 35-40 miles per hour it doesnt do this and will reach speeds over100+ miles per hour quickly without the stall. There's no way I'd race anyone with this happening because I'd most likely get burned.
Question: Is this due to the factory chip or is it being caused by the optispark? I have had the car put on a computer and the only thing we've found that may be causeing a problem is that when we scoped the fresh air intake pump it showed signs that the brushes were worn and causing the car to give a EGR Error reading from time to time. The pump still pulls the right amount of voltage but ever so often the service engine soon light will come on at slow speeds I.E. 30mph and lower. By shutting of the engine and waiting 5-10 seconds the light resets itself and doesnt come on again until a later time. Sometimes not for a week or so. Any insight to solving this problem would be helpful. Like I said I'm new to the 4th Gen F Bodies so yeah I guess you could consider me without a clue. This car is fast for stock. I know its potential is far greater than what I'm seeing. Help me bring it to life. Thanks

there are tons of possibilities on this
 

definately do a search..

for me it was the coil wire... brittle after 70K miles.

New coil wire solved it... Then I did plugs and the remaing plug wires from the set I bought..

Most common cause for the symptoms you state are "opti spark"...

good luck

JT

From the prior owner of this car I have been told that it had a 100,000 mile tune up i.e. new plugs, wires, etc. If this is the optispark would replacing it solve the problem or are there additional things that need to be done? I'm not stupid just new to this particular set up.

What code are you getting? Have you checked anything like fuel pressure to rule out this? You might try changing the fuel filter and check all the routine maintenance items to be sure there in good working order. The pcv value might need replacing also.

You will have better luck with this on the "LT1/LT4 Engine Tech" forum. I'll move it there for you...........

The secondary air pump, or AIR system, will not affect how the engine runs. The AIR system only operates for a couple minutes ate startup, to help the cat(s) heat up faster, then it goes off. If the system blows a fuse, it will set DTC 29, but other than that, you will not know the AIR pump is not working. There was a factory recall on the 95-97 LT! AIR pumpp systems.

The AIR system and the EGR system are totally separate, and a problem with the AIR pump will not cause the EGR code to set. The EGR code is common at low speeds/low engine loads, because that is the only time the EGR system gets turned on, so that;'s the only time the code will turn on the SES light.

Get the exact code.

OK this clears up some of the questions. Eliminating the air pump as a problem. When we scoped the air pump and read the error code I don't recall the number but I do remember it saying EGR error. Guess I'll have to run another test to determine the number. More money....shoulda paid more attention the first time I guess. I thought maybe the computer had been programed to govern itself above 5000rpm. (Don't even know if thats possible, as I said I'm new to this set up and dealing with computers. I'm from the old school of open the hood and see the motor. lol) A.K.A. my old faithful 69 Chevelle SS with 396, Muncie 4Spd, 411 rearend. But I want to learn and hopefully with the help of the people on this site I will succeed in getting where I want to be. Since the car is stock I have a long way to go and a lot of money to spend but will get there eventually. I do however want to keep it street legal.

Worn plug wires
Worn opti
Worn valve springs

Oh yes in refrence to the air pump fuse. I did find out about the recall on that and the GM dealership rewired the car with the new 30 amp fuse block. Mainly because of the pump being worn it was blowing the stock 20 amp fuse.

I'm sure you've already ruled this out but I put 87 octane in mine one day because thats all the gas station sold and I was on E. It would act like it was hitting a rev limiter at high rpm and seemed to run fine everywhere else. Filled up with premium and some octane booster and fixed it.

You may have something there. Next fill up I'll use 91 octane and a bottle of octane boost and see if things change. Thanks

Will try 91? Do you usually run 89? LT1s like 93. That's what's recommended if you can get it.

Have had to replace any coolant lately?If so,then your water pump(sits directly over your distributor(optispark),is bathing your opti,and shorting it out.Hope this helps.When up on a lift,look at the bottom of the water pump.:cool:

Not loosing any fluids, optispark is dry. i have been running 87 octane due to gas prices. Owners manual didn't show a recommendation of 93 if it did I missed it, but will double check. The highest octane available here without going to the airport is 91. So I will try a tank of that with octane boost. Anyone know what the general increase of octane for a 15 gal. fuel tank might be by adding a bottle of octane boost? And maybe a prefered brand?

octane booster is a gimic, just get 91 or better grade gas

You Owner's Manual recommends that you use premium unleaded fuel, rated 91 octane or higher. It notes that you can go as low as 87 octane, "but your vehicle may not accelerate as well." Check out page 6-4.

Octane requirement will vary with elevation (high altitude = lower octane requirement) and with ambient air temperatures (low temperature = lower octane requirement).