Okay so let me try to start this out in a good manner seeing as I've been thoroughly aggravated with this car since November I bought this car in Florida it's a 92 with the LT1. originally one day I was driving in the rain and it just died out simple as that it would run when it wasn't humid and it wasn't rainy but as soon as it got rainy or humid out the car would stall I tracked it down iand noticed if you sprayed any kind of water near any of the harness near the computer the computer would just crap out. so I assume the computer I sent the computer out to Cardone biggest mistake in the world... they send it back it wouldn't run after that... So sent it back again. 3 times. Got fed up. I don't even think they gave me my right computer back. So autozone got me a repacement from bluestreak. Still wont run. Got a custom $200 prom thinking maybe that would fix it. No luck. Car cranks. Just wont turn over. N since getting computer replaced. Dash has never showed my milage anymore. Just says "0" im wondering if the computer came from a 91 or 94 as 92-93 interchange. Any way to tell or anyone have any input as to what to do next? Im near pittsburgh pa. And Ive had it with gm and there crap excuses for cars.

 

With all of this being debated I do have a couple questions though that may lead to the solution.


From what I've been told there's a handshake made between the ECM and BCM is it possible that the BCM and ECM that were originally in the car came from another car therefore when I replaced just the ECM it's looking for the handshake and getting an invalid passcode because it's program to my vin and it doesn't have the BCM's handshake. I'm only asking this because I hear the mileage is programmed in there so it has to be making a proper handshake.

 

Doesn't much Soundlike Im going to get a response here lol

 

That doesn't point to a problem with the ECM but a problem with the wiring.

Very rare for the eprom to go bad.
Put the original back in.

You mean the engine turns over but doesn't start?

Post the part number on the computer case. 92-93 's are interchangeable.

If you are talking about the odometer reading that information is contained in the Body Control Module also know as the CCM.

You first need to verify no error codes are set.

Short pin A to pin G on the diagnostic connector located above the
drivers right knee. Turn the ignition On and look at the speedometer
LCD.

Module 1 is the CCM
Module 4 is the ECM

Post back what you see. C12 and ----- are not errors.

If no errors you need to check for spark and fuel.

When you crank the engine, does any rpm display on the tachometer?

 

1. C32 C34 C36 C38
H27 H32 H34 H36 H38

Yes car rolls over but wont start. Old prom back in. Got new battery mileage displays now. No start.

 

You didn't say what Module the errors were for.

If the errors are for Module 1 the CCM

27 LCD Blanking Control Circuit Open or Shorted
32 LCD Data Circuit Open or Shorted
34 Data Clock Circuit Open or Shorted
36 Data Strobe Circuit Open or Shorted
38 M Clock Circuit Open or Shorted

These are all dash cluster related failures. Usually from a low charged
battery.

If the errors are for Module 4 ECM

27 Quad Driver Module Circuit #2 Used to monitor 2nd, 3rd 4th gear.
Obviously that's not your problem since the car doesn't run.
32 EGR Problem. Probably not your problem because the car doesn't run.
34 Map sensor voltage low. If this is a problem you can disconnect
the Map sensor connector and the ECM will use a fixed Map value and the Throttle Position Sensor to control fuel delivery.
36 Optispark High Resolution Signal failiure. Engine should still run by
using the Low Resolution signal. So if you were to pull a spark plug there should be spark at the plug.
38 There is no ECM 38 trouble code.

Have you checked for spark?
Have you checked fuel pressure?

For a fuel problem manually open the throttle body and spay some starter fluid into the
intake. Does the engine try to start? If it does you need to verify with a fuel pressure gauge
what the fuel pressure is. Low or no fuel pressure could indicate bad fuel filter, pump or fuel pressure regulator.

For no spark you need a volt meter.
Set meter to DC and at the Ignition Control module located on the passenger side of the intake
manifold. Disconnect the four pin plug.

With ignition On you should measure around 12 volts from Pin A Pink/Black wire to Pin C Black wire which is ground. If no 12 volt verify the 10 amp coil fuse is good.

If those measurements test good with plug still disconnected, set the meter to AC.
Measure the voltage on Pin B White wire while cranking the engine. Should change from 1
to 4 volts. If it doesn't the problem is the ECM or the Optispark.

With out a scope only thing you can do is to take some voltage measurements at the plug on the passenger side of the Optispark. Disconnect the plug. Turn the ignition On.

Verify there is 12 volts from the Yellow wire to the Black/Pink wire on the connector plug. That tells you power is getting to the Optispark.

 

So reading your post because I have a similar but not same no start. Yours is a DIES issue.
I am leaning on your issue as a wiring/ECM connector terminal/or opti issue. does your tach read when you turn it over?
Anyway, I am about to post my question here and you may be able to find some things out from any of the responses I get as well. 92's are pretty fussy.
Good luck, I will think more about yours as I write mine, there are some pretty darn smart Techs on this site.

 

Okay getting 12 V DC I'm not getting ac voltage changing from 1 to 4 V as a matter fact I don't think I'm getting one volt most the time now down on the OPTi spark I'm getting nothing at all no voltage to the yellow wire all. And something to add the onboard computer it says my key is not in the ignition when ignition is turned forward but if you slightly turn it back while it's in the on position it says the keys there I don't know if that could cause an issue though. I did try to take voltage readings with the Keyturn forward and slightly turn back but had no difference in results.

 

So the opti is NOT a mag pulse generator. An A/C wave form is not what the EST signal is on these. The signal from the photo sense will be a digital square wave EST signal through 2 wires 1) Lo Resolution (less windows on opti slotted wheel for cam reference) BLK/Red Circuit 453 to green plug socket 5 at the ECM, 2) Hi resolution (most little windows for RPM) PPL/Wht circuit 430 to same green plug socket 14 at the ECM.
The power to the Opti is the yellow circuit 631 green plug terminal 18 at the ECM. This should be constant and I think is supposed to be 12 V (Though book says reference voltage) but I think that's just how they word it and is not 5 Volt reference voltage. but not sure yet.
While dealing with mine, I discovered unrelated wiggle tests at the ECM connectors that had contacts with resistance at the crimp(s) to the contact (in the plug), a couple failed the drag tests Socket in plug Not good contact to pin on ECU, and one wire that was damaged.
I have my entire dash out and looking for serial data circiut 800 splice S222, but admittingly have had a lot of distractions keeping me from my beloved 92 Vette. It too is effected all summer with its little occasional no start as result. I have not updated my post until I have it FIXED, but saw yours pop up.
So you sent your ECU out, it must be OK now. I would use the correct "chip" at least until you resolve the no start.
When you turn the engine over with a scan tool on data stream you should see a RPM, or even some lift on your tachometer signal if the opti is working.
Hoping this helps on the opti part of your diagnosis.

 

When you disconnect the 5 pin connector at the optispark and use a meter with one proble on Pin D Pink/Black wire and the other probe in the Pin C Yellow wire you should measure 12 volts with the ignition On.

If you don't verify the ECM 5 amp fuse is good located in the passenger side end of dash fuse panel.


Are you running the CCM key in ignition test? That switch can be flaky but won't cause a no spark or starting problem. It's used by the chime module and to program the PKE.

I'm looking at a 93 service manual so the optispark harness pin out shows.

Pin A Black/Red wire is Low res signal
Pin B Purple/White wire is the High res signal
Pin C Yellow wire is ignition feed
Pin D Black/Pink is signal ground
Pin E I believe is a shield wire and only used on a 92 harness.

 

Hooked on Vettes - your 93 manual matches my 92 FSM as well.

 

36Volt can you unplug the connector at the optispark and probe the Yellow wire with the ignition on and verify the voltage?

 

Good morning,
Yes I will do that very shortly, leme sip some coffee.
So you are talking about the opti connector passenger side of engine intake manifold yellow wire reading key on... will do.

 

Yellow wire (terminal C) I get battery voltage (12.5V battery is not fully charged now)
Also:
Pin A Black/Red wire is Low res signal
Pin B Purple/White wire is the High res signal
I found these have 5V reference from ECM as well. Apparently the photo cells when forward biased by the light pull the 5V to ground then back again to create the digital square wave. This would be called a "pull down" signal.
side note:
Many digital systems use pull up or pull down, even module serial data pre-CANbus.
Older Serial data depending on manufacturer could be pull up or pull down.
Pull up - circuit idle is zero induced signal is voltage rise (usually 5 volts)
Pull down - circuit idle is reference voltage and induced signal is a ground pulse.

 

Yes I don't have no power at those two wires I check the fuse fuses good.

 

If you disconnected the 5 pin Optispark plug at the side of the plenum, are you measuring the Yellow wire that goes back towards the firewall and not the end that goes to the Optispark?

Measure the voltage at the ECM 5 amp fuse with the ignition On.
Should be 12 volts. If you look at the top of the fuse there are two exposed metal contact test points on the fuse where you can take your measurement. Both test points should be 12 volts

You can use the cigar lighter outer metal shell for your ground probe.

 

Okay I have an update it seems my meter was pretty messed up that quit measuring out of nowhere anyways there is in fact power going down to the yellow wire the harnesses kind of shaky though the pins are rusted out I'm gonna try to replace the harness and then report from there I didn't verify voltage but the test light shows there's power going to it

 

Okay I got the harness ordered would you believe just for the connector with four little wires hanging out of it not even a harness just the connector is $60 ????

 

Ya, I would believe that. Hope that fixes it.

 

So I have some good news it seems the wire going to the distributor was the culprit had to clean off the connections as well because they were corroded next step is figuring out what's wrong with the digital dash it lights up sometimes sometimes adult if you tap the Dashboard it will turn on but even with that working the speedo doesn't ever do anything the gas gauge functions as it comes in and out but I guess that's next to fix