I diagnosed an intermittent no-start to my opti.

The first time i drive the car on any given day, the opti correctly provides a signal to pcm (i have a multimeter wired up to the low res signal) I can even agressivly drive the car, and aside from some intermittant higher rpm misses, the car runs well. If i stop and turn off the car for a few minutes, then start it up again (like to fill up gas for instance) opti still provides low res signal and everything is fine. BUT If i park the car and let it sit for 1-2 hours, the car either 1. wont start b/c the opti does not provide a low res signal or 2. will start but only run for a minute or so and then dies, throwing a Low Res Signal SES code. I have confimed with the multimeter that when the car doesnt start, it is because the opti provides no signal to the PCM. (furthermore, if i unplug the opti harness and probe the pcm side of the low res wire with the ignition on, i read the correct 5v value, so its not the pcm)

If i let the car completely cool off for 3-5 hours or overnight, the whole story i told you repeats.

The opti has failed on me occasionally while driving, which sets the Low Res Signal SES light and kills the car.

The engine does not appear to be running at an abnormally high temp. Highway is about 180deg, stop&go traffic it will get to 210 maybe 220 if it sits long enough.

This is a brand new GM opti that i put in about 1month/2000 miles ago. It was problem free until about two weeks ago when all of this started. I have two questions:

1. What is it about letting the engine heat soak while parked that causes the optical portion of the optispark to fail?

2. Will replacing the opti solve the problem, or is there some bigger heat-related issue here?

-Kyle

 

The optical encoders are solid state (p-n junction) devices. Any solid state device can go out at any time. Think of a light bulb that goes out when it's turned on. More often the failure of these devices is either caused by or is further aggravated by, heat. We see it with ignition modules a lot. Luckily heat related failures can be tested for easily with a heater and some freeze spray. But not in your case.

What I can't understand is how you can see the feedback signals with a multimeter. Does it have some sort of graphing feature to show the wave form in a type of o-scope fashion?????? The feedback signals are much to fast for a multimeter to respond to. Please explain.

 

Check the end of the opti harness that plugs into the OPTI for corrosion

Also did u replace the vacuum harness that attaches to the bottom of the opti? If the vacuum restrictor goes bad.. that round thing in the middle of your vacuum tube goes bad it can allow full manifold pressure on your opti. Your suppose to get a new one with the opti. if u did not get a new one harness with the opti you should beable to return the opti and get a new one for free and buy the vacuum harness because you were sold a opti without a new vacuum.

 

I just set the multimeter to read AC volts. It takes an RMS value of the square wave sent out by the opti. If the opti is sending a signal , the meter reads a constant 1.86V, if there is no signal it reads 0V. I ran the probe wires into the passenger area so i can monitor the signal while i drive/crank the engine. Ideally i should use an o-scope, but this was the best i could do for now.

Can corrosion cause a heat-related problem?? The car runs fine when its been sitting overnight.

No i didnt replace any of the vacuum harness -- I boutght the opti from GM, and it did not come with it. It was supposed to???

Whats interesting to me is that i had a vaccum leak develop at the PCV valve about a week before my opti started showing signs of trouble. I have since fixed it, but it didnt seem to help the no-start problem. Could this leak have caused the opti to prematurely fail?

 

Corrossion can kill the signal from opti to pcm. Its really easy to check just pull the plug and look down into the opti with a flashlight to see if there is any blueish crystalization on the connectors. Also look on the end of the wiring harness that plugs into the opti.
This is not likely the case. because once this happens the car wont start.. ever. But it can and will kill the connection while your driving and just stop your car like u stated.

no the pcv wouldnt have damaged the opti.

Also that Opti electrical harness... Disconnect it from the PCM and see test it to make sure its ok.

CHeck that stuff first.

PM me about getting a new opti. Im at work gotta go