Replaced opti and month later same no start and hesitation. Dealership insists the opti is good even with two opti codes(High and low resolution pulse) Could my coil or ignition module be to blame? Thanks.

 

Neither of them, but a bad connection to the PCM, or a PCM error could throw those codes.

 

That's what the dealer told me but I didn't believe them. Guess it's diy diagnostic time. Thanks.

 

To diagnose a bad Optispark:

1. Yank off your main ignition wire and test if it's getting spark from the coil while you crank. Spark should jump out of this wire to ground. If spark tests good here but not at any of the other plug wires, then the Opti is toast.

2. If even the main wire doesn't get spark, make sure the other half of the Optispark (namely, the optical trigger) is doing its job; this means check to see that the PCM is relaying the trigger signal from the Optispark to the coil module. Unplug the coil module, locate the correct pin on the connector, and check for incoming AC voltage while cranking. No AC voltage means a bad Opti, defective PCM, or poor connection between the two.

If there is AC voltage, but yet no spark at the main wire, your Opti is fine and your coil and coil module, or your main ignition wire itself, or related wiring are to blame. More tests can eliminate the wiring.

 

Louis is right... but allow me a shortcut - check the coil wire, too.

The thing is, the opti codes are either opti related or they are PCM related.

 

Although I mentioned the coil wire up there as something you might narrow things down to, really in this case since your Opti is throwing codes, it can't be the coil wire or coil or any of that, and here's why. The optical sensor part of the Optispark is actually completely separate from everything else in there, and has nothing to do with routing spark. The optical sensor simply watches the cam all the time and sends back a square wave signal for the PCM to do whatever with. Overall you can think of the OptiSpark as two completely unrelated parts crammed into one case. Any codes that deal with the Opti deal with that optical portion, since that trigger is what goes to the PCM. On the other hand, if the spark-routing part of the Optispark fails, the computer has no idea that the spark isn't getting to the right place other than that the car won't start, so no codes are thrown.

Upon actually reading your post, you say there's high and low resolution pulse codes present. As I described, that's the optical sensor's job and it's totally not doing it. Assuming that it's actually plugged in (it's likely not, check the connector tightness) and the PCM isn't fried (unlikely given your case) or unplugged, you need to replace that Opti.

 

There have been some cases, rare though, where someone had the high-voltage coil wire too close to the Opti-Spark low voltage wiring harness extension.
The induced voltage from the coil wire caused noise in the low-voltage Opti-Spark wiring causing Opti-Spark low and high res codes to be thrown.

Try moving the high voltage coil wire far away from the Opti-Spark electrical harness.
The '92 Opti-Spark harness had an electrical shield around that wiring (that's why the '92 has a six pin connector under the right side injector cover), but GM discontinued that in later years.

Another problem for some is chronic re-occuring corrosion in the Opti-Spark electrical connector right at the Opti-Spark -- they say it turns green inside.

Tom Piper

 

My connector was green when my Optical trigger pooped out on me. I reckon that implies that the delicate sensor components beneath the socket also had some corrosion. That may be why mine failed.

Also, speaking of the high voltage wires, in general always make sure your high voltage wires are placed orthagonal (perpendicular/90 degrees) to any other wiring harnesses. This way it cannot induce a current in those harnesses, because the magnetic field its own current induces twists in a way as to only induce current in things at least partially parallel to it. It's not always possible to route the high voltage wires the recommended several inches away from all the important sensor wiring, so in a lot of cases you just have to resort to letting them touch and making sure they're very close to 90 degrees to each other.

 

First I want to thank you guys for all your help. I got into an accident on Last Tue. in my other car and need the 'Vette to run now. I should hev given more info in my first post but I wasn't thinking... I(Dealer under thier warranty) replaced the opti five times in two years. Usually with four codes and my tach and ASR going crazy. Two opti codes, p0372, and p1371. Other two I don't remember but they were MAF related. Usually a no start condition and or major misfire. Now I have the four codes(Dealer says high and low resolution MAF and p1441 which I knew about) and it runs fine at times. Stalls at times and won't start for a few hours or maybe a day. Dealer says when it stalls the injectors continue to flow fuel into the motor and the pcm "keeps time". Which I assume means the pcm thinks the motor is still running. They say they plugged in a new opti after a stall and the same thing happened so it's a wire or pcm. They refused to replace the opti stating it was operating fine. I said if you plug in a new opti after a stall, the computer still is operating thinking there was a problem and plugging a new opti wouldn't change that until it saw it was running without the problem. So it would need to restart and run. They said I was wrong. Time is now an issue and I might buy a pcm and see what happens. Running down a bad wire(which I've never done) sounds like it could take a few days. Should I try replacing the pcm and see what happens? Thanks for help guys!

 

Simple and relatively easy wiring check is to unplug the wiring harness at the opti and then at the other end under the pass side fuel rail cover.
Then check all wires for continuity. This short harness is at high heat area and while not prone to failure it is maybe the easiest place to start.

 

It's brand new. Dealer said it was bad so I replaced but it didn't correct the problem. Thanks though

 

What did you pay for it? I got quoted $200 from the parts department for that little wire. Surely he had made a mistake and clicked the wrong thing, but he insisted that it was the price, and I walked out in disgust. I bet I could buy a kit to make 10 of those for under 30 bucks.

And one more thing, your symptoms of running fine at times were similar to mine with a bad opti. Opti symptoms have incredible variety; it may or may not start, may or may not make the tach go crazy, may or may not continue pulsing the injectors, may or may not keep running once started, may or may not run consistently rough, it goes on and on. The opti could do any number of things depending on how far along it is damaged. It's really hard to conclude things based on the symptoms alone; a multimeter is the only true way to diagnose a bad opti, and even that only eliminates everything but the Opti and PCM. You need an oscilloscope and test harness to prove which of those two is bad, or you could just note that your PCM shows no unusual behavior and generally seems pretty happy and intact other than what pertains to the opti.

 

If you're getting low-res and high-res Opti failure codes, one or more of these faults will be the cause:

1. Pulses are not being generated by the optical sensors in the Opti. This could be due to failure of the optical module, or due to a mechanical failure internal to the Opti unit.

2. Absent power feed to the Opti.

3. Absent ground feed to the Opti.

4. Open circuit between the Opti and ECM/PCM on the high-res and low-res lines. If these codes both appeared at the same time, a wiring harness fault seems unlikely, as this would be quite a coincidence (unless the harness got munched by mice, a connector pair got separated, etc).

5. Failure in the ECM/PCM in the signal input circuitry that receives the low-res and high-res pulse trains from the Opti.

Do have a look at the proximity of the coil wire to the Opti harness, as Tom Piper advised. He has noted numerous times on this forum that he is aware of one or more cases where this caused problems, and if he says it's so, you can bank on it.

If you don't have the diagnostic skills, tools/equipment, and a factory service manual, I recommend you get this car to the best diagnostician you can find -- one who knows these cars very well or one who really, truly does know how to read and understand the information in the service manual and is expert in troubleshooting electrical system malfunctions, and is equipped to do so. Sadly, most autmomotive technicians simply don't have the understanding of electronics that is required to efficiently and accurately isolate and repair this type of fault. Hiring a true expert will let you out the other end $$$ ahead of where you'll be if you either throw parts at the problem or hire somebody who isn't up to the task. An ace diagnostician with an oscilloscope and DVM should easily be able to isolate this fault for you within an hour or two of raising the hood. Time and cost to repair it will depend upon its cause.

Best of luck with it.

Live well,

SJW

 

I think I paid $120-$130. Dealer wanted $240. Got mine from gmpartsdirect.com. Usually they take a long time to ship parts but I got the harness in a week!

 

I got mine on ebay for $30. It fits and works perfectly.