Can someone help me in trouble shooting my Opti. I have a no start problem in my 94 MT. It just died out of the blue. I do not have spark at the coil. I pinned out the ignition control module and everything but the terminal C (AC Signal) checked out ok. Can someone tell me what the pin outs are for the opti connector so I can check there. I am mainly looking for the low signal pin. The car does not give any codes indicating a problem. Coil and ICM check out fine. I think it is either the opti low side or the pcm since it ran fine and then just died. Started up, ran for a short time fine, and then died again. Now it won't start at all. Thnxs for any help you can give.

 

This does not sound like an Opti problem, It sounds like a bad ICM. This is the little black box that is bolted to the ignition coil bracket.

 

I thought so to but I swapped it out with a known good one from my friends car and still nothing. Based on one of your past post terminals A and B are 5 volts on the opti connector and Terminal D is ground. These check out OK. Does this mean that terminal C is the low side signal from the opti? How can I check that? Does this need to be connected when I check it? Is there such a thing as a coil and ICM not "matching"? They are both OEM but I only changed out the ICM with anther OEM.

 

I don't have my manuals here to refer to today, but if the low-res signal is faulty, you should get a code (16, if I recall correctly). A high-res signal fault will also set a code (36, IIRC).

I would tend to agree that this probably is not an Opti failure.

Be well,

SJW

 

I sure hope it isn't the opti since I just put in a new dynaspark last summer. Since the car ran fine when it did run and just died without warning I think I can going to look closer at the ICM and PCM. The wiring and connector all look good, clean, and tight. Thanks

 

Well you have a good start but let me help you some. Your 5 volt measurements on A & B of the opti don’t mean anything unless you looked at it with a scope and rotated the engine. That opti section does not fail much. It drives the PCM so lets look at the PCM output which drives the ICM which is a easy signal to measure. These tests out of book I have just re-worded it.

Here are a few tests to get you started on the problem. Be the utmost of careful not to short anything to ground. ING key off, remove ignition module connector and check the ground connection on pin C - BLK/WHT wire, (resistance about 0) .

Next, “Key on”, check for 12 volts DC at pin A - PNK /BLK wire and pin D – Dark green wire. If no voltage check the coil fuse 10A, (#25), or wiring.

If all is good, set meter to read AC volts and connect probe to terminal B - white wire. Have some one crank engine, meter reading should be between 1 to 4 volts. Key off! Put connector back on. If OK, this indicates opti and PCM are probably working. If not, opti or PCM could be source of problem. Figuring out which one might take some doing and would be phase 2. *If you make this measurement on terminal B with a scope you should see about 4 -5 volts p-p. ***

If all is good, the IGN coil should put out spark. Remove high voltage coil wire from coil. Attach another wire from coil and hold near ground while some one cranks engine. If is arks, other wire could be bad. If it does not ark ICM or coil could be at fault Since you tried a ICM that could point to the coil. There is no matching. I’m running a Auto Zone coil myself, I do have 2 OEM ICMs. Check these items and see how you do.

 

Thanks for all the great help. Here are the findings from the ICM pin out.

Ignition control module (ICM) - Key OFF
Pin C - BLK/WHT wire, (resistance about 0) should be ground = good ground with .2 Ohms

Ignition control module (ICM) - Key ON
Pin A - PNK /BLK wire, should be 12 V = 12.13 V
Pin D – Dark green wire, should be 12 v = 12.14 V

Ignition control module (ICM) - Key ON CRANK ENGINE
Pin B - white wire (AC Volts setting) should be 1 -4 V = .005V AC setting .016 V DC setting

This looks like the problem is before the ICM which would be the opti low side or PCM. I should get a code for the low side opti problem but I do not get any codes at all. What tells the PCMwhen there should and shouldn't be an opti low side signal? Is there another crank sensor to tell the PCM to look for the low side opti signal?

 

I have a scope to look at the low opti signal. Does anyong know the pin out of the opti connection (the one on the pass side of the manifold)?

 

This is a very interesting question. I don't have my manuals with me now, but I pulled the following info from http://www.troublecodes.net/GM/94_57P.shtml

Code 16: A low resolution pulse was not detected by ECM within 720 high resolution timing pulses.

Code 36: ECM detected less than 40 high resolution timing pulses between each low resolution pulse for 5 consecutive cycles.

This raises the question of whether or not the ECM will note any anomaly if it receives neither low-res nor high-res pulses from the Opti, and I don't know the answer to this. I'm guessing it may not detect a fault if both signals are completely absent. The FSM may be able to shed some additional light on this.

If you can get an O-Scope on the Opti signal lines, you should be able to quickly determine whether or not the Opti is furnishing any pulses to the ECM.

Also worth checking, especially if you don't have an O-Scope available would be the power/ground connections to the Opti.

Please post any follow-up info/results, as I'm sure many of us could benefit from what you learn about this.

Be well,

SJW

 

Looks like you posted this while I was composing my previous reply. Good to hear you have a scope.

I don't have my FSM here now, but with Google's help, I found the following info buried on this web page:

http://lt1tech.com/cgi-bin/ultimateb...c;f=6;t=003885

The low-res signal wire is PIN 2 on the BLACK PCM connector. It's a Red wire w/ black stripe.

Hopefully this is accurate info.

If you have low-res pulses, and no low-res DTC set, the Opti should be feeding the ECM enough info to at least start and run the engine. The ECM can run the engine with no high-res pulses detected, but will not run the engine without low-res pulses. In your case, the ECM may very well be seeing neither (in which case, I'd suspect a harness fault on the power or ground line, as it seems unlikely to me that both of the Opti's optical sensors would fail at the same time, but ya never know, especially if they took a voltage spike).

Good luck.

Be well,

SJW

 

Just to double check to make sure we don't go off in a wrong direction, since you have a scope there, I would like you to recheck pin B of the ICM connector. Set the horrizontal on scope slow rate and crank the engine and try to lock up any signal if there is one there.

From my 94 book, - Post updated fixed errors.

***PCM pins are on PCM connector labled BLACK ***
Opti - pin A - low resolution signal (red/black) to PCM pin B2
pin B - high resolution signal (purple/white) to PCM pin B20
pin C - 12 volts DC input power (red says the book but my color is yellow) to PCM pin B14
pin D - Ground - (pink/black) to PCM pin B3

These signals must be measured with connectors connected and not removed.

What I have done to make measurements in the past is to take a straight pin (like from a sewing kit) and slide it down along side of the wire into the connector where it will make contact with the metal pin down in there. I found this is the least destructive way to tap into an circuit. Pin D of the opti should be the highest pin or closest to the coil wire connector.

check the PCM fuse #33, 5A, if it blew the PCM is not going to do anything, probably not even throw a code.

There is no other crank sensor.
Doing good so for

 

If an opti causes a sudden failure it will usually set the above code.I too do not feel it is an opti issue.If you have done the proper FSM testing for the ICM my money is on the coil.ICM's can have wiring issues that is why it is important to do the tests.

 

One place to always check when there is no spark is the connection that sits between the injectore on the passenger side of the manifolf.
This harness carries all of the signals between the ECM and the ciol/ICM/opti.
Unplug this harness where it connects between the injectors and check for corrosion or a loose connection.

 

Ok, I was trying to use my scope to check the opti signal when I noticed something strange. With the key on the fuel pump would prime but then seem to blip and prime again. It would do this before but I thought it was just trying to keep the pressure. As soon as I disconnect the opti to ecm connector on the side of the manifold it stopped. Plug it is back together it blips. I put my spark detector on the end of the coil plug with the connector together and blipping. I was getting random sparking. I put the coil wire back on the opti and the car fired up and ran great but died out of the blue (same symptoms I had before). The fans also came on right when it started which shouldn't happen.

Is there a filter for the low level resolution? Could the PCM be getting a dirty signal. With the fuel pump going on an off and random spark I am baffled. I would say it is a ground but I the ground on the opti- pcm test good and I also put on a secondary ground with no difference. What would the opti connection do with fuel pump blipping. The more I think about it, the more I think it is the PCM. Still no codes. When I ran, it ran great. Nice and smooth, steady idle.

 

Wow - don't know where to start. Don't want to go off in 6 different directions. Well, if you have a fuel pressure gauge I would measure the pressure for starters. I know you said you had no codes but if there was one, the computer will start the fans as a safety measure. I measured my pin B on the ICM connector and it indicated 1.5 VAC with a DVM as I cranked the engine. If that signal is not there, there is no drive pulse for the ICM and coil to make Hi-volt. It's real important to make sure if you have it (pin B) or you don't or you will go off in a wrong direction and waste time.

I would tend to agree with the others that the opti is OK as an opinion. Just wanted to provide you with as much information as possible if you needed it. Hope you checked out the PCM fuse...basics.

As for the fuel pump, no warn fuzzy. Its like the pump relay kept getting energized which is driven by the PCM.....humm. Take another look, need to narrow the search, can't go off in 6 directions.

** In thinking about this for a while, the fans running, the pump re-cycling and no signal voltage on the pin B all are PCM related and seem to point to the PCM doing strange things.

 

I have a fuel pressure gauge on the rail and when the pump primes it goes to 42psi. When the fuel pump relay blips it jumps. I checked a few other things last night.

Opti pin C (DC input power) = 12.10V
Opti pin D (Ground) = tested good for a ground

I will try to get the scope on the opti to PCM wire as well as the PCM to ICM wire to see if they match and see if the PCM is giving the same signal or if it's doing its own thing.

Again the big thing I found strange was the random spark coming from the coil wire with just the key on and not cranking. The PCM must have given a signal to the ICM for some reason.

 

All of the symptoms you're seeing suggest that the ECM is doing strange things. I'd suggest you check all connections/fuses associated with the ECM. If you don't find anything wrong, jostle some connectors, etc to see if you can find an intermittent contact.

It's quite possible that the ECM is failing, but with so many connections to/from the ECM, I'd try to exhaust all other possibilities before I bought a new one. Maybe you can get lucky and find somebody in your area who has a spare ECM that you can swap in as a test.

Good luck. Keep us posted.

Be well,

SJW

 

I worked on the car a bit last night. Since I was able to get it started for 2 minutes the other night I decided to check out the code situation again. I did get a few history codes this time. H36 and H72. I know H3 is the high resolution of the opti but I knew something was screwy with that. H72 is gear selector switch. This is strange. Right at the begining of all this stalling and no start problem I had another history code for engine oil over temp (can't remember the #). I'm wondering if this is another finger point at the PCM. It is throwing strange unrelated codes, as soon as I hook up the opti to the pcm the fuel pump relay (during priming, key on, no cranking) blips, and I get random sparking at the coil (again without cranking the motor). When it ran it ran nice and smooth and but just dies out of the blue after 2 minutes.

Since the strange things stop when I disconnect the opti at the side connector, I'm going to see if I can plug my old opti in at the connector just to see if the strange happenings continue. This may help eliminate the opti internals more.

 

This was posted by Jerris on 03-06-2006:

Contrary to popular belief, on a 92 LT1 the cause of an intermittant code 36 is NOT a bad opti. The opti almost never comes back to life when it goes out.
According to the 92 FSM, the cause of intermittant code 36 is usually a bad connection between the opti and the ECM.
The FSM says to "CHECK EST WIREING FOR ROUTING TOO CLOSE TO THE SECONDARY IGNITION COMPONENTS OR OTHER COMPONENTS THAT MAY INDUCE ELECTROMAGNETIC INTERFERENCE ON TO THE EST SIGNAL WIRE THAT MAY CAUSE A FALSE EST SIGNAL TO THE DIS SIGNAL TO THE DIS MODULE.
THE DIS FAULT LINE WILL BE IN THE LOW STATE ANYTIME THAT THE IGNITION MODULE DETECTS A FAULT THAT FORCES THE IGNITION MODULE TO GO BACK TO BYPASS MODE.
AN INTERMITTANT CONNECTION CAN CAUSE AN EXTRA EST SIGNSL AND SAT A CODE 36.


This may explain my false signals and random sparking at the coil without cranking the motor. I do have (for over a year) a new set of Taylor wires. Everything seems to be routed OK. I move the wires away from things. I may try sheilding each component to see if it helps eliminate any interference.

 

I seriously doubt that you have an issue that will be helped by shielding the plug wires, or an issue with the plug wires themselves. If RFI or EMI from the plug wires is getting into the low-voltage system somewhere and causing problems, it's probably a result of a deficiency somewhere in the low-voltage system that's making it uncommonly susceptible to this. This is among the last places I'd begin looking for the cause of your problems.

As Jerris suggested, take a very close and hard look at the Opti harness connection on the right side of the intake plenum. Scrutinize this carefully for any signs of corrosion, a loose or sprung pin, a recessed pin, etc. Also try wiggling this connector to see if any anomalies come & go while it's being jostled. Do the same with the harness where it meets the Opti.

If you find nothing there, scrutinize every connection at the ECM, and then begin checking connections elsewhere.

Check/tighten/clean all engine and chassis grounds next.

Then check all fuses -- not for blown fuses, which obviously would not produce intermittent faults, but for loose/overheated/corroded connections between fuse & socket. We very recently had a C4 owner here on this forum who traced the source of some truly bizarre electrical gremlins to an overheated contact at one of the heavy fuses under the hood.

I think you're on the right track, and I have a hunch you're gonna nail this bug very soon. Keep us posted.

Be well,

SJW