1994 Z28 stock automatic....

Driving along highway last week at 65, went to give it a bit more gas, and all of a sudden 0 RPMs....just coasting for a few seconds, and then it kicks back in without having to restart the engine.....

Happens again a minute or two later, and then again.....get off highway....on side road, it happens again, and then I stall completely....get it to restart a couple of more times until I am pulled over waiting for a tow.

Around the last time it stalled, I started smelling the cats, but I think it's more to do with what was going on inside the engine than the cats themselves....

Anyway, took it to a shop, they pulled the following codes:

o 16-Low Resolution Pulse Failure
o 42-Est Grounded
o 36-High Resolution Pulse Failure

They said they idled the car for a while, and it screwed up badly again. Then the next day, they said they had the car idling for THREE FREAKIN' HOURS (which pissed me off), took it out for a road test, and nothing...not a peep....they said the car ran great (which it does, despite being almost 14yo and having 164,000 miles on it).

They did no work on the car except explore for a possible reason and didn't find much:

· all contacts wet, and oil soaked.
· Checked fuel pressure & volume….ok!
· Check opti-spark connector and harness for corrosion….OK!
· Check opti-spark high resolution signal and found frequency produced half of what specification is….clear code and road test vehicle….vehicle runs fine with no hesitation or stumble present at this time…..

After hearing they idled the car for 3 hours, I took it away from them, drove home (25 miles) without incident, stuck it in the garage for four days, and then took it to the dealer where I usually go. They said they found a loose wire going to the distributor which they tightened, and then injected dye into the engine to see exactly where the oil leak is coming from. I was told a month before this that the engine is leaking from the intake, valve covers, front cover, and water pump gasket, but that the dealer didn't want to go around changing all these seals because the engine is old and it might cause leaks to develop elsewhere due to pressure changes?

This car is running on its third opti-spark, so I wonder if that is dying on me again (water pump gasket leak sounds like it might be potential trouble for the opti-spark).

Any other ideas why the car would do what it did, and then one day later act as if nothing happened?

Thanks in advance!

 

You mentioned water pump gasket, that would be a coolant leak not oil. I had bad water pump drive seal leaking oil, the oil worked it's way onto the slotted disk in the opti, car died running at 50 MPH and would not restart got it towed home it started the next day ran two weeks died again with Hi resolution code. I replaced the WP oil seal, put in a new opti, and new opti harness cable. Tore the old opti apart and found oil on the optical wheel and pickup. IMO don't waste money on a new opti until you invest time or money to fix the front cover and wp seal leaks.

 

You're right....it's not leaking coolant, so it must be the water pump drive seal...my mistake....thanks for the reply...

 

Lo Res Fail = Opti

Better check that WP seal!

 

A follow-up:

I took the car back to the dealer, and they put some dye into the oil to track where the oil leaks are coming from exactly. They told me to drive it for 2 weeks, then come back.

Well, I took it to work one day (25 miles back and forth), and then decided that wasn't too smart, considering it could stall out without warning while driving, so I decided to drive it around close to where I live. Shortly into week 2, the car died on me again, so I stopped driving it and took it back to the dealer (had to have it towed, as it died on the way to the dealer, about 10 minutes into the trip).

Dealer says the black light when shone on the engine showed NO dye, no oil leaking at the moment (perhaps I did not drive it long enough?) They also said it is definitely my opti-spark causing the stalls, as they were able to reproduce the problem, and they put a new opti into the car. They opened up the old opti, and told me there wasn't any oil or water or coolant to be found inside (and when I say "old opti", it's not old at all....less than TWO YEARS old and only 13,000 miles have been driven since the last one was put in back in 9/06).

The rep looked over my records and saw that I had an opti put in Sept 2006 and also one in 2003. He called GM, AC Delco and some other rep and none of them would cut me a break on this replacement, although he said he would "only" charge me $575 for the opti (his "cost", or so he says) instead of $700...

The kicker in all of this is that back in 2006, I had my coolant changed by this same dealer, and shortly after, the opti died. This April, I had to have my coolant hoses changed because they were very soft, thus the coolant had to be replaced again (and I was promised by their Corvette tech that he wouldn't get the opti wet), and lo and behold, we are where we are today, with another opti being put into the car.

Thus, this opti makes it #4 for this car (including the original). I know why the original opti went bad, because I made the mistake of going to jiffy lube once, where they also changed the coolant (I wasn't aware of the opti's track record at the time)....but who knew this would happen at the dealer as well, not once, but twice....

And to think, I even warned them before they replaced my coolant hoses this time around (April) to make sure and keep the opti DRY....in fact, at first they told me they wouldn't do a coolant change because they couldn't guarantee they would be able to keep the opti dry! Can you believe that?

But when they saw the condition of the hoses, they had their Corvette tech tell me he wouldn't get it wet...

This whole thing seems like a giant, pricey joke....I'm more than pissed....is there anything else I can do, except fire off some letters to GM and Chevy? Not that that will do much good.....

 

Instead of paying more morons to keep ripping you off why don't you invest into some wrenches and learn how to take care of and maintain your car. Theyarethere to make money and obviously you don't mind payingthem. Why would you ever pay $575.00 for a part you can get for almost half of that straight from GM yourself, and then pay them tools to install it for god only know how much more.

 

I'd take this as a "lesson learned"... If you're paying $575 for an opti, I can only assume you're paying another $400 (or so) for installation... so, $1000 at the end of the day, and you're realizing that the quality of the work isn't there... IMO, I'd do what gatorhead suggested, and do the work yourself.

Buy some tools, a new GM Opti from Summitracing.com, and a Haynes manual, and get crackin'! That's what I've done over the past three - four years. Started off afraid to change a lightbulb, and now I'm ready to pull my motor.

Good luck man!

 

Maybe check the ICM (the thing your ignition coil is bolted to). Mine was running fine one day and all of a sudden died like that. It did it a few more times over the new week until it finally died for good. After replacing the ICM, no problems at all.

 

Uuh huh - what Gator said. There is plenty on info on this site as well as others, on how to change the opti. There are also quite a few knowledgeable gearheads here who can give you pointers if need be .

Just out of curiosity, have you ever had the opti wiring harness changed? Just because it's not corroded, doesn't mean that it's making good consistent contact. Their connectors been known to go bad. Oh - and it's a $40 part and takes a long-blade screwdriver and about 5 minutes to change.

 

I know nuffin! I agree with the connector theory as well and its worth a try, but highly unlikely. If I could get a grand evry six months I might have a tendency to drip something in there if I were dishonest. The difference between a stealership mechanic and and outside mechanic is the stealership mechanics are certified GM thiefs lol.

 

I would tend to agree with the "accidental drip" theory if they had come back at me and told me they found oil, coolant, water, whatever in the opti. But they said they found nothing in there....

I've been going to these guys for 10 years and never felt like they were ripping me off before. In fact, the one time I took the car to an independent shop is when I felt I was being ripped off....

The codes that I mentioned in my original post....they are opti-related, correct? Would they also be thrown if the ICM or coil were going bad?

Every other time the opti failed on me before this, the car would usually only bog down under heavy acceleration. It wouldn't just cut out on me like it's doing now, although I have read that stalling out is also a symptom of a bad opti.....

Here's something else I haven't mentioned before that might shed some light: whenever the car would stall out recently as described above, I would often wait a few minutes and try and restart it, sometimes successfully. As I would turn the key to the halfway point (the point at which the gauges would activate and the warning lights would light, but not far enough to actually start the car), I have noticed that the tachometer would flip up and down quite dramatically, in a way that was not normal...keep in mind I haven't even attempted to start the car at this point, I've simply turned the key halfway. Why would the tach flip out like that at that point...the engine isn't even engaged yet? Is that a sign of something else other than the opti?

 

The other GM's that I have come in contact with have done the same thing with the tach because of poor current flow from the battery. In most cases it was due to a bad connection at the battery. Usually when the tach would freak out, it was accompanied by a "clicking" sound.

Don't forget there are numerous connections that can all do the same thing. Particularly the ground strap from the left cylinder head to the frame that no one ever checks.

A poor battery connection, either on the positive or the negative side can play hide and seek as you mentioned. It can also give all sorts of random errors. ALSO, if the alternator is leaking AC out onto the DC supply line, it can cause all sorts of weird problems. It's easy to check. Put the meter on AC voltage at as low a scale as possible. Measure from the negative battery terminal to the output post of the alternator. There should be less than .03 VAC present. Just an FYI.