guruerror

Hello...hopefully someone here can help with my prob.

I've got a 93 Z-28 LT1 (83,000) which was off the road for about 2-3 years and has now developed a problem where the idle is a little rough, occasionally sputtering and dying while idling, and occasionally buck and sputter during normal driving; typically on the freeway between 1,500 and 2,500 RPM.

When the bucking and sputtering occurs, the Check Engine light will come on and I'll have to slip the transmission into neutral, give the engine a couple of revs to temporarily resolve the issue (for a few miles). When the problem gets real bad (making the car nearly undrivable) I pull over, turn the motor off and back on to resolve the issue...there have been several times when this would not resolve the issue either and I've let it set overnight -- it then starts without a hitch and I'm back at square one.

I first took it to the family mechanic who reported a 'high resolution pulse error' being stored in the computer. This mechanic gave the car a complete tune-up (plugs, wires, etc.) and even put a new distributor and cap on (AC/Delco).

Drove fine for a few days...then started back up. Took the car back to the same mechanic, he tried a new PCM (AC/Delco). This smoothed the idle out but it still cutoff twice. When this mechanic tried to get codes from the new computer his equipment could not make a connection to the replacement PCM...so I had him replace the original PCM and took it to the dealership.

The dealership replaced the vacuum hoses and claimed the car was done. Drove fine for a day (still had the rough idle - but had more power)...cut off a day or two later.

The dealship has now had the car for one week and claims to have 'no clue.'

ANY help would be GREATLY appreciated.

Thanks in advance,
Brent

white97T/A

have you replaced the coil and ICM?

what about the fuel, have you checked the pressure?

WS6T3RROR

high rez or low rez errors for that matter are opti related. and i'd say the reason the car cuts out is because without those signals the pcm cuts the fuel to the motor because it assumes it isnt running. you should try to replace the entire opti not just the cap and rotor because the way i understand it that isnt typicly the part that fails its a piece that you cant replace without swapping out the whole assembly. the other thing to check would be the computer harness that goes to it which also tends to corrode up sometimes, but be careful taking it apart its been hot plenty of times and will probably be extremely brittle.

guruerror

The dealer made no mention of checking the coil or the ICM. I'll pass that along.

Regarding the Opti...pardon my ingorance...but isn't the Optispark the same thing as the distributor? The first mechanic said the he replaced the complete distributor and the cap.

guruerror

Okay...I just got off the phone with the dealer. They've got their Corvette guy looking at the problem. They are currently checking the ICM and coil.

I asked about the Optispark (again with my limited understanding of this unit) and told them that the car just had a new distributor and distributor cap installed. The service manger reported that the Optispark is not 'part' of the distrubtor...that it is seperate, and has quoted about $1,700 for that unit.

Someone PLEASE educated me before I give up and a used Chevette to drive to work.

trans9_5am

Here is a little info:

http://shbox.com/1/4th_gen_tech2.html#opti_test

http://shbox.com/1/93-94_opti.jpg

http://shbox.com/1/optical.jpg

Find out for SURE that the complete opti was replaced. It sounds to me like the cap and rotor were the only things replaced and not the optical sensing unit but thats just a guess. Again just throwing stuff out there but how old are your O2's?

Brandon

WS6T3RROR

1700 for an opti? you're ****ting me. they're like $390 bucks for the early ones. NAL-10457702 is the part number in summit for the early one from gm. and its really not that hard of a unit to swap out the guys i know who have had problems with them can change them out really quickly. my guess is still that you're pcm isnt seeing a proper signal from the opti and its cutting the fuel off for the motor. the harnes to the opti is about 40 dollars if i remember rightly also and it should be checked for corrosion.

shoebox

High resolution problems are going to be one of two things in 99% of cases:
-the distributor (not referring to cap or rotor portion)
-the wiring harness to the distributor

A complete GM opti (distributor, including cap and rotor) for your car can be had for about $300.

The person who told you that is a complete fool, lying, wants all your money or all of the above.

guruerror

Given that the unit is only $390...I'm assuming the remainder would be labor ($1,310). I know that there is a lot of disassembly to get to the unit (I watch my previous mechanic do the job)...but that still seems high.

AND my previous mechanic says that that's what he replaced...could it be that this item already went bad? If so...is there something else wrong that could be causing repeated units to fail?

shoebox

If it was replaced with a GM unit, it would have a one year warranty. No one can predict the lifespan of a part (especially one that has electronic components).

Injuneer

Check the wiring.... corrosion on the harness terminals can cause problems, as Shoebox has already pointed out. If you really got a complete Opti replacement, and it didn't solve the problem, its worth looking at the harness connector on the Opti to see if its damaged. Also check the gray "Opti test connector" on the bracket on the passenger side of the intake manifold that also supports the EEC purge solenoid.

Charging TA

As soon as I read the original post the first thing I thought was wiring harness, Id completely replace the wiring harness from the computer.

Two or so years ago I was working on a almost-new-at-the-time Audi, the car had gone to a "German car specialist" for fluid changes. They had for some reason disconnected the battery and had tried jump-starting the car (you cannot disconnect the battery on VWs/Audis/Mercedes/etc without having a pigtail cigerette adapter plugged in). So the car went to a Audi dealership, and they could not figure it out after a month, so the owner brought it to one of my clients who is a mechanic, he asked me to look at it and I did. First thing I said is that its the wiring harness, because we could not get the computer to read. The mechanic did not really believe me, but tried testing the wiring harness. A few weeks later I heard that the car had been taken to a Audi dealership an hour away, the problem ended up being the wiring harness.

The car would run and such, but you would have to manually shift the automatic and such.

93zted

try some different gasoline. Mobile ,Cheveron and Exxon have better detergents in them. The fuel injectors inthese engines clog easily. check fuel pressure by installing a pressure gauge on the rail to get a reading . 37lbs is what the GM book says but they run a lot better @40-42 lbs. Any car that has sat around for long periods of time can have partially clogged or "dirty" injectors which can cause some of the driveability problems you describe.

HBHRacing

Bad gas isn't going to cause hi res failure.



Where are you located? I would highly recomend another shop. Any one that works on GM's should have at least a basic understanding of how the optical spark dis works and how to repair them. Even when we suply parts and labor we only charge around 800 for an opti install. If the dealer can't understand whats going on then it's time for someone else to look at it. I can literaly diagnose that code in less then 3 mins. Check a 5 volt refference and then a wave form and I know if the opti is sending the high res pulse or not. For a compitent tech it's a very simple matter.

Fastbird93

Like has been stated before, if it's a DTC 36 High Resolution Pulse faulty code being thrown, it's 99% of the time the opti or the harness. Of note, the car should still run good with a DTC 36 present, says so right in my 93 Service Manual: "The engine does not need the high resolution pulse to operate."

Personally I'd double check the cap and rotor that were installed. It's generally perceived as a terrible idea to just replace those two components of the opti instead of the entire thing.

From the way you were describing your problem however, it almost sounds like you're having ICM overheating issues. That's the first thing I thought of.