Voltage readings on opti harness?
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From: S Fla
Voltage readings on opti harness?
My car has been quitting while I'm driving. 94 6 speed. No warning of any sort. It's running right up until it's not.
Here are the voltage readings from my opti harness.
Pink never has voltage. I believe it is the ground.
Red always has either battery or alternator voltage. 12 to 14 volts.
Purple/ white and red/black both have 4.9v dc when key is on the run position and when cranking.
Purple/white has 2.5v dc and 2.1 volts ac when it's running.
Red/black has 1v dc and 1.8v ac when it's running.
I tried multiple grounds to be sure I was getting a good reading. They all gave the same numbers. Also, all readings were the same in both sides of the connector, even when I was moving it, trying to see if the signal would change.
Here are the voltage readings from my opti harness.
Pink never has voltage. I believe it is the ground.
Red always has either battery or alternator voltage. 12 to 14 volts.
Purple/ white and red/black both have 4.9v dc when key is on the run position and when cranking.
Purple/white has 2.5v dc and 2.1 volts ac when it's running.
Red/black has 1v dc and 1.8v ac when it's running.
I tried multiple grounds to be sure I was getting a good reading. They all gave the same numbers. Also, all readings were the same in both sides of the connector, even when I was moving it, trying to see if the signal would change.
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From: Cape Coral, Florida
Hope some or all of this video helps !!…on almost all GM’s I’ve seen a pink wire is normally a power feed…where in South Florida are you located ??…I saw you posted last year about this issue.
Last edited by C5 Diag; Mar 22, 2023 at 11:30 PM.
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From: S Fla
Thanks, C5 Diag. Sorry I didn't respond sooner. It's a secondary car, and it's been a hectic couple of weeks. I finally got back into it and verified that my opti readings are the same at the ecm, so there are no problems with bad wiring or connectors. I'm thinking it might be my ecm. I'm losing both fuel and spark, but the ecm is getting the inputs it needs. I can get a blank ecm for around, or under $100. I've started experimenting with tuners, so I can save the tune from my current ecm and upload it to the new one. I've also found that I have no idea how to use a tuning program.
I'm on the south side of West Palm.
I'm on the south side of West Palm.
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
My car has been quitting while I'm driving. 94 6 speed. No warning of any sort. It's running right up until it's not.
Here are the voltage readings from my opti harness.
Pink never has voltage. I believe it is the ground.
Red always has either battery or alternator voltage. 12 to 14 volts.
Purple/ white and red/black both have 4.9v dc when key is on the run position and when cranking.
Purple/white has 2.5v dc and 2.1 volts ac when it's running.
Red/black has 1v dc and 1.8v ac when it's running.
I tried multiple grounds to be sure I was getting a good reading. They all gave the same numbers. Also, all readings were the same in both sides of the connector, even when I was moving it, trying to see if the signal would change.
Here are the voltage readings from my opti harness.
Pink never has voltage. I believe it is the ground.
Red always has either battery or alternator voltage. 12 to 14 volts.
Purple/ white and red/black both have 4.9v dc when key is on the run position and when cranking.
Purple/white has 2.5v dc and 2.1 volts ac when it's running.
Red/black has 1v dc and 1.8v ac when it's running.
I tried multiple grounds to be sure I was getting a good reading. They all gave the same numbers. Also, all readings were the same in both sides of the connector, even when I was moving it, trying to see if the signal would change.
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Joined: Jul 2016
Posts: 67
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From: Morganville NJ
My '93 Opti was fine until I think it got wet. Gen I version. Your problem may or may not be Opti based. I decided to just get it rebuilt or bite the bullet and get a Petris.
The rebuild was done and fixed all my issues. The bearing was going and it needed the cleaning. Sealed and upgraded to Gen II with MSD cap.
If you are good until it gets hot, there could be a few more issues. I decided to do the Opti first, new water pump while it was off and change plugs and wires. As you know, the Opti requires the water pump and balancer to come off. I only wanted to do this once.
The rebuild was done and fixed all my issues. The bearing was going and it needed the cleaning. Sealed and upgraded to Gen II with MSD cap.
If you are good until it gets hot, there could be a few more issues. I decided to do the Opti first, new water pump while it was off and change plugs and wires. As you know, the Opti requires the water pump and balancer to come off. I only wanted to do this once.
Le Mans Master
Joined: Sep 2013
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From: near the thumb in the mitten
Opti doesn't operate like conventional distributor ignition. Opti sends 2 reference signals to PCM. PCM sends signal to ignition module and sets.up injector pulse. 94 has Sequential Fuel Injection opposed to batch aka Multi Port Fuel Injection. There was a post about testing Opti references with an oscilloscope several years ago. I don't remember who did it. A guess would be 93 ruby
Team Owner
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From: Park City Utah
I agree that an DVOM isn't going to be that useful. I also agree that an oscilloscope is the BEST way to test the opti; you can actually watch the two signals and see the size of the low res windows.
But the cheapest/fastest, test is to look at your tach when the car dies, but is still rolling down the road w/the engine turning. If the tach is at "0", that is pretty strong evidence that the opti has stopped working.
But the cheapest/fastest, test is to look at your tach when the car dies, but is still rolling down the road w/the engine turning. If the tach is at "0", that is pretty strong evidence that the opti has stopped working.
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From: S Fla
Thanks for all the advice. I've finally got a little time to look at the car, and talk with you who are trying to help me.
1st. The tach does go dead when the car stops. So here's a question. The reference signals come to the computer. The computer then send signals to the ignition module and the injectors. What about the fuel pump? I lose power to the pump (measured on the pump side of the connector at the tank) and the ignition. If the fuel pump voltage is not directly enabled by the reference signals from the opti, then I either have a different issue or multiple issues.
Speaking of multiple issues.... the car no longer cranks when I try to start it. Brand new battery. $200 😡🤬😡🤬 I remember paying less than $100, more suddenly it's twice as much. I have power to move the seats, turn on the radio, run the windows. Just nothing going to the starter. Could an issue with VATS be causing my problems?
That brings up something else. I downloaded Tunercat, TunerPro, EEHack (didn't work), and Flashhack. I wanted to turn off VATS just to be sure, but have no idea how to even input the bin into them. I think I copied my current tune with Flashhack. There's some other file (ADX or something, not looking at it right now) that I don't know how to import, either.
Fun, fun
1st. The tach does go dead when the car stops. So here's a question. The reference signals come to the computer. The computer then send signals to the ignition module and the injectors. What about the fuel pump? I lose power to the pump (measured on the pump side of the connector at the tank) and the ignition. If the fuel pump voltage is not directly enabled by the reference signals from the opti, then I either have a different issue or multiple issues.
Speaking of multiple issues.... the car no longer cranks when I try to start it. Brand new battery. $200 😡🤬😡🤬 I remember paying less than $100, more suddenly it's twice as much. I have power to move the seats, turn on the radio, run the windows. Just nothing going to the starter. Could an issue with VATS be causing my problems?
That brings up something else. I downloaded Tunercat, TunerPro, EEHack (didn't work), and Flashhack. I wanted to turn off VATS just to be sure, but have no idea how to even input the bin into them. I think I copied my current tune with Flashhack. There's some other file (ADX or something, not looking at it right now) that I don't know how to import, either.
Fun, fun
Drifting
Joined: Jun 2020
Posts: 1,355
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From: Northwest Ohio
Fuel pump will not run continuously if engine not running. Only fuel pressure matters (do you have it and how much).
When you turn to key on, does the security light go out on the dash or stay constant on? If it shuts off it is not VATS.
You need to test at the starter to see if it is getting voltage during crank. Do you hear any clicking at all when you go to start?
You may have a bad ground too…remove and reattach your battery cables (clean them up first) and make sure they are tight on the battery. Measure voltages from several spots to ensure good voltage. There is also a bus/block by the battery that can corrode. Unhook and clean up the wires/terminal.
I had my car go completely dark when attempting to crank due to a poor battery cable connection on a brand new battery. Cleaned and made tighter and no issue.
When you turn to key on, does the security light go out on the dash or stay constant on? If it shuts off it is not VATS.
You need to test at the starter to see if it is getting voltage during crank. Do you hear any clicking at all when you go to start?
You may have a bad ground too…remove and reattach your battery cables (clean them up first) and make sure they are tight on the battery. Measure voltages from several spots to ensure good voltage. There is also a bus/block by the battery that can corrode. Unhook and clean up the wires/terminal.
I had my car go completely dark when attempting to crank due to a poor battery cable connection on a brand new battery. Cleaned and made tighter and no issue.
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From: S Fla
Here come the edits, for things I forgot to mention.
Heat does not seem to be part of the issue. It will stall before it's even warmed up. Sometimes it will start again immediately. Sometimes it takes quite a while.
Heat does not seem to be part of the issue. It will stall before it's even warmed up. Sometimes it will start again immediately. Sometimes it takes quite a while.
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From: S Fla
Fuel pump will not run continuously if engine not running. Only fuel pressure matters (do you have it and how much).
When you turn to key on, does the security light go out on the dash or stay constant on? If it shuts off it is not VATS.
You need to test at the starter to see if it is getting voltage during crank. Do you hear any clicking at all when you go to start?
You may have a bad ground too…remove and reattach your battery cables (clean them up first) and make sure they are tight on the battery. Measure voltages from several spots to ensure good voltage. There is also a bus/block by the battery that can corrode. Unhook and clean up the wires/terminal.
I had my car go completely dark when attempting to crank due to a poor battery cable connection on a brand new battery. Cleaned and made tighter and no issue.
When you turn to key on, does the security light go out on the dash or stay constant on? If it shuts off it is not VATS.
You need to test at the starter to see if it is getting voltage during crank. Do you hear any clicking at all when you go to start?
You may have a bad ground too…remove and reattach your battery cables (clean them up first) and make sure they are tight on the battery. Measure voltages from several spots to ensure good voltage. There is also a bus/block by the battery that can corrode. Unhook and clean up the wires/terminal.
I had my car go completely dark when attempting to crank due to a poor battery cable connection on a brand new battery. Cleaned and made tighter and no issue.
I went out to check on the security light. The car therefore decided to start.
Will our cars have the block in the same place? I can't remember what year yours is.
Time to sit in the car and listen to the stereo for a bit.
Team Owner
Joined: Aug 2004
Posts: 21,543
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From: Park City Utah
1st. The tach does go dead when the car stops. So here's a question. The reference signals come to the computer. The computer then send signals to the ignition module and the injectors. What about the fuel pump? I lose power to the pump (measured on the pump side of the connector at the tank) and the ignition. If the fuel pump voltage is not directly enabled by the reference signals from the opti, then I either have a different issue or multiple issues.
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Joined: Aug 2021
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From: S Fla
What pedricd said. If you loose opti signal (indicated by your tach dropping out)....AND at the same time, you lose fuel pump, that is a very strong indicator that you've lost your crank/cam signal (the opti). The fuel pump should continue to run w/the engine rotating b/c of the oil pressure switch, but that may have failed a long time ago.
Even so, the oil pressure would raise enough during cranking to allow the fuel pump to come on.
What am I missing?
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From: S Fla
Even when this car is a pain, it's pretty cool. My 11 year old son came out and is hanging out in the car with me. Fun cars are the best. Even broken they're good. 😁
Also, it's not starting again. The security light is on, and stays on.
If I could figure out how to set up and use TunerPro, I'd turn off VATS and see what happens.
Also, it's not starting again. The security light is on, and stays on.
If I could figure out how to set up and use TunerPro, I'd turn off VATS and see what happens.
Team Owner
Joined: Aug 2004
Posts: 21,543
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From: Park City Utah
This part....
I was trying to avoid confusion but probably complicated the issue. If you were using the fuel pump as an indicator that you're opti died...ECM lost crank signal and shut down the FP relay and pump....you could be misled if the engine were still spinning (in gear, car moving) b/c the engine would still have oil pressure, and thus, the oil pressure switch would (should) be sending power directly to the fuel pump. So, you'd still see power at the pump, and perhaps conclude that the power is from the FP relay/ECM when in fact it would be from the oil pressure switch.
If the car loses power to the pump at the same time the engine quits firing, then I'd say the OPTI died, and the oil pressure switch had also checked out...probably a long time ago.
I was trying to avoid confusion but probably complicated the issue. If you were using the fuel pump as an indicator that you're opti died...ECM lost crank signal and shut down the FP relay and pump....you could be misled if the engine were still spinning (in gear, car moving) b/c the engine would still have oil pressure, and thus, the oil pressure switch would (should) be sending power directly to the fuel pump. So, you'd still see power at the pump, and perhaps conclude that the power is from the FP relay/ECM when in fact it would be from the oil pressure switch.
If the car loses power to the pump at the same time the engine quits firing, then I'd say the OPTI died, and the oil pressure switch had also checked out...probably a long time ago.
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From: S Fla
I pulled the codes. All 3 were historical. On section 1, it had H51 and H53. In section 9, it had H72. So, I have for H51, Calibration error mem-cal, ecm or EPROM failure.For H53, I have Battery Voltage, Low/High/Error or EGR valve solenoid, circuit error.For H72, I have vehicle speed sensor lost. Does any of this make a bell go off?
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From: S Fla
This brings something else to mind. I've been getting a Low oil level light intermittently. Scares the heck out of me, because the car is relatively new to me and I've had cars that should be full show no oil at all when I checked them. But, when I check this car, it's always full. Then the light goes out. Until it comes back on again. Stupid thing. I've got the new sensor, but just have not installed it. Could it be involved?
Drifting
Joined: Jun 2020
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From: Northwest Ohio
Security light staying on when key is in run position is a VATS issue. It won’t start when this is occurring.
All your rando issues could point to bad connections/grounds etc… have you checked and cleaned them? Maybe try reseating your PROM.
But I also suspect you are doing a lot of cranking with running the battery down etc. and introducing phantom non-issues as a result.
I think you need to restart troubleshooting. Disconnect battery and charge it to 100% first. Don’t crank it endlessly. With a fully charged battery and the car reset this way do you have VATS issues?
All signs of your running issues (ie after getting started) seem to point at loss of opti signal…. Either the opti/harness, bad signal to noise ratio (grounds/connections/interference) or something with the ECM.
All your rando issues could point to bad connections/grounds etc… have you checked and cleaned them? Maybe try reseating your PROM.
But I also suspect you are doing a lot of cranking with running the battery down etc. and introducing phantom non-issues as a result.
I think you need to restart troubleshooting. Disconnect battery and charge it to 100% first. Don’t crank it endlessly. With a fully charged battery and the car reset this way do you have VATS issues?
All signs of your running issues (ie after getting started) seem to point at loss of opti signal…. Either the opti/harness, bad signal to noise ratio (grounds/connections/interference) or something with the ECM.
Drifting
Joined: Jun 2020
Posts: 1,355
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From: Northwest Ohio
I pulled the codes. All 3 were historical. On section 1, it had H51 and H53. In section 9, it had H72. So, I have for H51, Calibration error mem-cal, ecm or EPROM failure.For H53, I have Battery Voltage, Low/High/Error or EGR valve solenoid, circuit error.For H72, I have vehicle speed sensor lost. Does any of this make a bell go off?
This brings something else to mind. I've been getting a Low oil level light intermittently. Scares the heck out of me, because the car is relatively new to me and I've had cars that should be full show no oil at all when I checked them. But, when I check this car, it's always full. Then the light goes out. Until it comes back on again. Stupid thing. I've got the new sensor, but just have not installed it. Could it be involved?