Opti question
Thread Starter
Instructor
Joined: Feb 2009
Posts: 204
Likes: 0
From: Pinellas Park Florida
You cannot look at all parts as having the same probability of failure. The ICM although connected to the coil and could have similar codes but the ICM fails much more than a coil. And also if you have read any amount of posts, the opti fails frequently as compared to the PCM. The PCM actually has a rather low failure rate and hardly ever hear of one actually being bad and correcting a problem. PCMs are actually very reliable unlike the ECMs in the earlier years. The opti fails left and right all the time.
I hope you have done some of the basics as suggested. The PMCs might be cheaper but harder to find. It bothered me you can't it to crap out in the driveway where you can take measurements. If you go for the PCM, I would hang on to my original one.
I hope you have done some of the basics as suggested. The PMCs might be cheaper but harder to find. It bothered me you can't it to crap out in the driveway where you can take measurements. If you go for the PCM, I would hang on to my original one.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
That is the frustrating part. My son is a service advisor at a dealership and gets the parts cheap. I will not be able to keep my old PCM unless I forfeit the core charge. He has gone through the flowcharts in the FSM. I still think that the new ICM is bad also. With the old ICM I get codes 36 & 42 when it stalls. With the new ICM I get a code 42 right after it starts up, and code 36 after it stalls.
I would just then replace the ICM. It's under $100 and easy and fast to replace. If you are wrong it's not bad having a spare ICM for the future.
I would much rather take a shot on the ICM than give up a "working" PCM that is factory programmed. IMHO.
Most of the time the opti does not just kill the engine and then go again. They usually make poor running, bucking and other delightful things. But there is no absolute for the symptoms and anything can go.
It's just that from the law of averages I would put the PCM on the low end of the list. It's a tough choice when following the FSM, but there has to be a mix of written information with knowledge and experience.
Thread Starter
Instructor
Joined: Feb 2009
Posts: 204
Likes: 0
From: Pinellas Park Florida
I don't normally takes shots but.....
I would just then replace the ICM. It's under $100 and easy and fast to replace. If you are wrong it's not bad having a spare ICM for the future.
I would much rather take a shot on the ICM than give up a "working" PCM that is factory programmed. IMHO.
Most of the time the opti does not just kill the engine and then go again. They usually make poor running, bucking and other delightful things. But there is no absolute for the symptoms and anything can go.
It's just that from the law of averages I would put the PCM on the low end of the list. It's a tough choice when following the FSM, but there has to be a mix of written information with knowledge and experience.
I would just then replace the ICM. It's under $100 and easy and fast to replace. If you are wrong it's not bad having a spare ICM for the future.
I would much rather take a shot on the ICM than give up a "working" PCM that is factory programmed. IMHO.
Most of the time the opti does not just kill the engine and then go again. They usually make poor running, bucking and other delightful things. But there is no absolute for the symptoms and anything can go.
It's just that from the law of averages I would put the PCM on the low end of the list. It's a tough choice when following the FSM, but there has to be a mix of written information with knowledge and experience.
My son is pretty good around cars but doesn't have experience with vettes. He is determined to figure out what is wrong without throwing parts at it. I have been letting him do it his way seeing as he is saving me a bunch of money. If it wasn't for him I would have to take it some place. I think that at some point I need to bite the bullet and take a shot at something and the ICM is probably the best place to start. I think that the Opti would be next although it cost more than a PCM. If it isn't the Opti a spare one would be better than a spare PCM.
Le Mans Master
Joined: Mar 2001
Posts: 7,999
Likes: 14
From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
Cruise-In III Veteran
Cruise-In IV Veteran
St. Jude Donor '12
Ask your son if he can go old school - put an ocilliscope on it.
I forget which pin from the opti is the low pulse and high pulse but he should be able to see nice clear digital wave forms. Then check the inputs and outputs on the ICM.
Mine was crappings out doing the following:
Run car for 20 - 30 min (disable the fans let it get into the 250 range)
shut it down, wait 15 - 20 minutes let everything get good and heat soaked
Start the car and see what happens - mine would stumble, rpm all over the place, almost die
OBTW - my problem was resolved with a new ICM and coil. Opti didn't go out until the water pump went. I have a new problem, it appears related to the emissions canister with lots of pressure build up in the gas tank.
I forget which pin from the opti is the low pulse and high pulse but he should be able to see nice clear digital wave forms. Then check the inputs and outputs on the ICM.
Mine was crappings out doing the following:
Run car for 20 - 30 min (disable the fans let it get into the 250 range)
shut it down, wait 15 - 20 minutes let everything get good and heat soaked
Start the car and see what happens - mine would stumble, rpm all over the place, almost die
OBTW - my problem was resolved with a new ICM and coil. Opti didn't go out until the water pump went. I have a new problem, it appears related to the emissions canister with lots of pressure build up in the gas tank.
Thread Starter
Instructor
Joined: Feb 2009
Posts: 204
Likes: 0
From: Pinellas Park Florida
Ask your son if he can go old school - put an ocilliscope on it.
I forget which pin from the opti is the low pulse and high pulse but he should be able to see nice clear digital wave forms. Then check the inputs and outputs on the ICM.
Mine was crappings out doing the following:
Run car for 20 - 30 min (disable the fans let it get into the 250 range)
shut it down, wait 15 - 20 minutes let everything get good and heat soaked
Start the car and see what happens - mine would stumble, rpm all over the place, almost die
OBTW - my problem was resolved with a new ICM and coil. Opti didn't go out until the water pump went. I have a new problem, it appears related to the emissions canister with lots of pressure build up in the gas tank.
I forget which pin from the opti is the low pulse and high pulse but he should be able to see nice clear digital wave forms. Then check the inputs and outputs on the ICM.
Mine was crappings out doing the following:
Run car for 20 - 30 min (disable the fans let it get into the 250 range)
shut it down, wait 15 - 20 minutes let everything get good and heat soaked
Start the car and see what happens - mine would stumble, rpm all over the place, almost die
OBTW - my problem was resolved with a new ICM and coil. Opti didn't go out until the water pump went. I have a new problem, it appears related to the emissions canister with lots of pressure build up in the gas tank.
Sounds like it is worth a try. The coil has already been replaced. I was getting a code 16 as well as the 36 & 42 before I changed the coil and ICM. Now code 16 is gone. Thanks.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
95-96 Photo LT4
Does anyone have a photo of the tubing, etc under the left fuel rail cover? I took a thousand photos of my R & R but not under there.
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Does anyone have a photo of the tubing, etc under the left fuel rail cover? I took a thousand photos of my R & R but not under there.
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
Jake
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Does anyone have a photo of the tubing, etc under the left fuel rail cover? I took a thousand photos of my R & R but not under there.
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
If you have one with the cover off of a 95-96 LTX or a 96 LT4, it would be a great help. Specifically the routing of the vent tubing from the opti to the intake.
Eddie
Jake
Last edited by JAKE; May 12, 2010 at 03:30 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Intermediate
Joined: Oct 2009
Posts: 31
Likes: 0
From: Austin TX
Oscilloscope
Just thought I'd chime in on my progress or lack thereof with the same problem. I put an equivalent to a scope on my car to measure three things:
Signal from the PCM to the ICM
High res signal from distributor to PCM
Low res signal from distributor to PCM
Low res signal is always there. High res signal was intermittent. I found that if I wiggled the connector under the right plastic cover (over top of the injectors), I could make the high res signal come and go. I jumpered a wire around the connector and now it is steady.
I found that where the wires from the distributor went into the main wiring harness, they go through a piece of plastic that seemed to pinch them a bit. I think this caused a break in the wire. You might have your son put a scope on these signals at different points on the wire and see if he can make them go away, especially when wiggling the wires or the connector.
Still, when I try to start the car, I have no signal from the PCM to the ICM for about 6 seconds of cranking, and then the signal appears and the car will start and run well. I do still get the following codes:
C12
H36
H42
H62
H64
H42 (ignition control circuit shorted) makes me wonder if something else isn't wrong that keeps the signal from the PCM to the ICM from being there.
Onward through the fog.
Signal from the PCM to the ICM
High res signal from distributor to PCM
Low res signal from distributor to PCM
Low res signal is always there. High res signal was intermittent. I found that if I wiggled the connector under the right plastic cover (over top of the injectors), I could make the high res signal come and go. I jumpered a wire around the connector and now it is steady.
I found that where the wires from the distributor went into the main wiring harness, they go through a piece of plastic that seemed to pinch them a bit. I think this caused a break in the wire. You might have your son put a scope on these signals at different points on the wire and see if he can make them go away, especially when wiggling the wires or the connector.
Still, when I try to start the car, I have no signal from the PCM to the ICM for about 6 seconds of cranking, and then the signal appears and the car will start and run well. I do still get the following codes:
C12
H36
H42
H62
H64
H42 (ignition control circuit shorted) makes me wonder if something else isn't wrong that keeps the signal from the PCM to the ICM from being there.
Onward through the fog.
Thread Starter
Instructor
Joined: Feb 2009
Posts: 204
Likes: 0
From: Pinellas Park Florida
Well after much testing and messing around with things I decided to go ahead and purchase a new PCM. I know some of you don't think that that is the problem, but I am at the point of needing to do something to get it back on the road. The PCM is cheaper and easier to replace than the opti. It has been ordered from GM and I should get it this week. I'm keeping my fingers crossed.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
for what it's worth, an opti is nothing more or less than a distributor and like all distributors the rotor and rotor cap need occasional changing. Back in the day, with a "conventional" distributor (as in easily accessible), this is done on a routine basis. not so with the opti's. I suspect many opti "failures" are in fact rotor and rotor cap issues. what I noticed most when I changed out the opti on my engine was just how badly deteriorated the cap and rotor were.
Le Mans Master
Joined: Mar 2001
Posts: 7,999
Likes: 14
From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
Cruise-In III Veteran
Cruise-In IV Veteran
St. Jude Donor '12
Just thought I'd chime in on my progress or lack thereof with the same problem. I put an equivalent to a scope on my car to measure three things:
Signal from the PCM to the ICM
High res signal from distributor to PCM
Low res signal from distributor to PCM
Low res signal is always there. High res signal was intermittent. I found that if I wiggled the connector under the right plastic cover (over top of the injectors), I could make the high res signal come and go. I jumpered a wire around the connector and now it is steady.
I found that where the wires from the distributor went into the main wiring harness, they go through a piece of plastic that seemed to pinch them a bit. I think this caused a break in the wire. You might have your son put a scope on these signals at different points on the wire and see if he can make them go away, especially when wiggling the wires or the connector.
Still, when I try to start the car, I have no signal from the PCM to the ICM for about 6 seconds of cranking, and then the signal appears and the car will start and run well. I do still get the following codes:
C12
H36
H42
H62
H64
H42 (ignition control circuit shorted) makes me wonder if something else isn't wrong that keeps the signal from the PCM to the ICM from being there.
Onward through the fog.
Signal from the PCM to the ICM
High res signal from distributor to PCM
Low res signal from distributor to PCM
Low res signal is always there. High res signal was intermittent. I found that if I wiggled the connector under the right plastic cover (over top of the injectors), I could make the high res signal come and go. I jumpered a wire around the connector and now it is steady.
I found that where the wires from the distributor went into the main wiring harness, they go through a piece of plastic that seemed to pinch them a bit. I think this caused a break in the wire. You might have your son put a scope on these signals at different points on the wire and see if he can make them go away, especially when wiggling the wires or the connector.
Still, when I try to start the car, I have no signal from the PCM to the ICM for about 6 seconds of cranking, and then the signal appears and the car will start and run well. I do still get the following codes:
C12
H36
H42
H62
H64
H42 (ignition control circuit shorted) makes me wonder if something else isn't wrong that keeps the signal from the PCM to the ICM from being there.
Onward through the fog.
If you don't mind me asking - what did you use instead of an ocilliscope to look at the pulses?
Intermediate
Joined: Oct 2009
Posts: 31
Likes: 0
From: Austin TX
I used my laptop with a data acquisition (DAQ) board from National Instruments: http://sine.ni.com/nips/cds/view/p/lang/en/nid/14605.
It's about $280, but it has several analog inputs. I just spliced into the wires and cabled them inside the car to the DAQ board which connects with USB to my laptop.
Just as a side note, I've seen this problem on a few forums where the AC goes out at the same time. I have a code (can't remember the number) that my oil temperature sensor voltage is low. That means the car thinks the oil is very hot and shuts off the AC. I'm not sure if this is related or not, as I haven't tested it, but it coincides on my car with the distributor problem and seems to coincide in other cars as well. I also have a code 42 which is an ignition circuit shorted. this happens when the high resolution pulse from the opti is absent for a certain number of revolutions, I think it's 80.
It's about $280, but it has several analog inputs. I just spliced into the wires and cabled them inside the car to the DAQ board which connects with USB to my laptop.
Just as a side note, I've seen this problem on a few forums where the AC goes out at the same time. I have a code (can't remember the number) that my oil temperature sensor voltage is low. That means the car thinks the oil is very hot and shuts off the AC. I'm not sure if this is related or not, as I haven't tested it, but it coincides on my car with the distributor problem and seems to coincide in other cars as well. I also have a code 42 which is an ignition circuit shorted. this happens when the high resolution pulse from the opti is absent for a certain number of revolutions, I think it's 80.
