You are getting reference but are you getting the correct highrez to lowrez ratio?

If you have access to a dual axis DMO, look at the overlay of the high and low rez off the opti. It should be a clean trace with 4 lows to each 180 high pulses, You can also compare the signal with the CrnkPS.

Corrosion will screw you up, I changed on opti only to discover it was the POS overpriced 50$ harness.

Simple guess, replace the opti cable. Bluish buildup is a sure sign (plus no codes and progressivly worse go/no go).

-Craig

BTW, there is an OBDII param that calculates the ratio of high to low but it is only so-so for diag

 

I had something like this happen once, I replaced everything you listed and replaced the icm 3 times.. gave up and took it to the dealership, it was still the icm. Apperantly the 3 I bought from autozone were all junk. I learned to only buy good electical parts that week.

 

are you sure the coil driver is working? when it dies, hook a DMM up to the coil input connector and look to see if its switching the coil on and off likes its suppossed to. the module is transistor based, and it is constantly swithing on and off and its supceptible to heat damage if it doesn't cool properly

 

Damn Jordon. I would deffinatly say opti but you have tryied two? Many times I will get cars in for no run and no codes. I will verify fuel, spark and injector fire. If you have fuel but no spark or injector fire = Opti. Spark plus injector fire but no fuel? I trouble shoot the pump and power to it.

Now there is also a little known fact about the Opti sending the signal to turn the fuel pump on We had this happen a few years ago while a car was under warranty. It may run a few days it may run 30 seconds. The Dealer had the car four times before the owner said "I aint paying another dime till you fix it!" (they kept nickles and diming him on top of warranty). He got tired of walking places while his car was stuck in the road. Turned out to be opti.

We have also had the opti harness screw us over. Looked fine, tested fine but in the end replacing it fixed the problem of dieing while driving down the road. The contacts evedently would get hot and not make contact.

No Code Present does not rule out the opti. If it looses power to run the optic's there will be no codes as the PCM just thinks the motor is not turning. Codes can only be set if one of the optic's ,high or low res, are working or if there is intermitant signal's.

Next time it dies I would run tests from the PCM on the Opti wires I am with you on it sounds like a wiring issue.

Good luck Jordon!

 

Thanks for that little explanation on alternative opti troubleshooting. I know I learned something new today!

 

I agree... good stuff Mr. McGroo.

-Mindgame

 

I had a similar problem with my car a few years ago. Car didn't throw any codes, sometimes it would start, sometimes it wouldn't. I also replaced the ICM a few times and installed a new coil. Also replaced the cap and rotor on the opti. Each part would fix the problem for a day or two, then back to the no start/shut off issue. The shop I took it to couldn't find it, they even gave me the car back and it died in their driveway. Anyway, the shop paid for a GM tech to test every part of the engine and it turned out to be a bad optical sensor even though there were no codes in the computer. I'm so glad I'm running an LTCC now.

 

My car does this too, last time it ran for 15 minutes in the driveway before dying and not starting again. I have had luck unplugging and plugging back in the opti harness on the side of the intake.

Anyone have the testing specifics for electrical testing at this location?

BTW- I have replaced the opti and the opti harness 4 times as well as the vaccuum harness trying to fix this problem. Also I am on my second PCM since this has been happening.

 

disconnect the oil pressure switch at the back of the intake manifold and crank the car. the PCM energizes the fuel pump for 2 seconds when it first turns on. after that, it deenergizes the fuel pump relay if there are no references signals coming from the opti. However, the car is designed so that if the fuel pump relay(PCM controlled, btw) goes out, sufficient oil pressure will close an oil pressure switch, providing voltage to the fuel pump circuit. this oil pressure switch is located at the back of the intake manifold. with its connector unplugged, if you crank the vehicle for 10 seconds and the fuel pump stays on the whole time, the PCM is powering the fuel pump relay because it is receiving signals from the opti. if, after cranking for 10 seconds the fuel pump shuts off after about 2 seconds, the PCM is deenergizing the fuel pump relay because its not receiving signals from the opti.

 

from there, you will know if its the opti or not. if its not the opti, its time to check voltages at the 4 pin connector at the Ignition Control Module(ICM). on the harness side, pin "A" should have batt voltage with key in run or start, no voltage otherwise.pin "B" is the output form the PCM that switches the ICM on and off so you should see a digital signal(i'm not sure what magnitude) while the car is cranking if the PCM is trying to spark the engine. pin "C" is a ground for the ICM. it should have good continuity with the 3 grounds bolted to the ICM bracket(the PCM gounds out here also), and all 3 grounds should have good continuity with batt ground. pin"D" is the ICM's output to the coil, switching it on and off as required. pins A, b, and C you can chek to see if they have the right signals coming form them(voltage between A and C with key on should be BATT voltage, B to C should show the digital signal while you crank the car). if all that is correct or pin A did not have BATT voltage, it is time to check the voltages at the coil connectors. there should be 3 or 4 wires (the 4th being a white wire used for a tachometer)there should be 1 white wire with a black stripe(pin "A" on the black connector{it may also be a green wire}); 1 pink wire with a black stripe(pin "B" on the black connector); 1 pink wire with no stripe or a black stripe(pin "B" on the grey connector); and maybe a white wire with or without a black stripe(pia "A" on the grey connector{for a tachometer}).pin B on the grey connector should have BATT voltage with the key on. pin B on the grey connector should have continuity with pin A on the ICM's connector(this wire carries BATT voltage from the positive side of the coil to the ICM, so if ICM connector pin A didn't have BATT voltage, this wire MAY be at fault). pin A on the grey connector goes to a tachometer input if its connected. pin A on the black connector will have a digital signal that switches from high to ground(this signal grounds the coil's primary side, turning the coil ON
{dwell time}, when the signals switches back high, it cuts the coil OFF, firing the secondary lead{coil wire}). the main thing on this circuit is that it is connecting and disconnecting from ground, cutting the coil on and off. after thatthe only other thing left is the coil itself. there are 2 sockets on a stock style coil(not counting the secondary lead's socket). one socket takes pin "A"'s from the black and grey connectors, the other socket takes the pin "B"'s. the side that takes the pin "B"'s is the positive side of the coil, and both its holes should have zero resistance between each other, if not, batt voltage that comes from the key on will not get to the ICM. the side that takes the pin "A"'s is the negative side, and both its holes should have zero resistance between each other. the connector colors(grey and black) that go to the coil may be reversed, but the specific pins(A & B) are the same. see these diagrams from Shoebox's webpage:
http://shbox.com/1/95_ign_system_schematic.jpg
http://shbox.com/1/harness7.jpg

 

I just want to pint out NONE of thiese test even the ones I typed up will work to find a problem un-less the car is acting up

 

any new word on the situation?

 

Ahh i am having the same problem on my 93Z. it died when i was driving. Then it started the next morning and ran for about 10-15 mins then died and now nothing. no spark. is getting fuel and signals, coil is brand new and fine (double checked coil) . the opti harnes checks out good and so on. After all the testing I've done i've come to the conclusion that either its wiring or the ICM which I am trying to get tested ASAP so I dont buy a new one for no reason. i guess the PCM could be bad too. need to test more.

 

Light it on fire????? haha jk

 

Did you visually inspect the harness on both sides? A meter test didn't show a problem for me but when I took off the weather pack on the opti side, the cause was easily seen. Same with buildup on the pins in the opti.