MAP sensor, and stumble question
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Joined: Jun 2001
Posts: 545
From: Tampa
Hi Don,
Thanks for your feedback. The car is not starting all now. It turns over but is not catching on. I think I'm going to buy a different Code Reader and see if my Innova is broken.
All the wiring I can get to looks good (no corrosion/broken pins/insulation etc). I have not been able to get to the one on the opti itself as it looks like I have to pull everything to get to that.
Since I have fuel pressure to the regulator even with no start how can I test injectors to see if they're good?
Thanks for your feedback. The car is not starting all now. It turns over but is not catching on. I think I'm going to buy a different Code Reader and see if my Innova is broken.
All the wiring I can get to looks good (no corrosion/broken pins/insulation etc). I have not been able to get to the one on the opti itself as it looks like I have to pull everything to get to that.
Since I have fuel pressure to the regulator even with no start how can I test injectors to see if they're good?
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Joined: Jun 2001
Posts: 545
From: Tampa
Update: just tried a new scan tool (Actron) which is supposed to flash the SES lights a number of times to indicate a code. Result: no SES flashing at all. I can hear the fans come on when the Actron is plugged in, but nothing blinking on the SES light, car still not starting.
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From: Hell was full so they sent me to NJ
You can not flash the codes on the SES light on any year LT1 except the 93. Your Actron "scan tool" is nothing more than a switch that shorts the two required ALDL pins together. It says on the box that it will work for a 94, but it WILL NOT WORK ON A 94. Even if you had a 93, all you need is a paper clip to short the ALDL pins, not the Actron "scan tool".
I would contact the manufacturer of your OBD-I/OBD-II scan tool to find out why its not working.
I would contact the manufacturer of your OBD-I/OBD-II scan tool to find out why its not working.
Thread Starter
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Joined: Jun 2001
Posts: 545
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Thanks Fred. I'll be taking the Actron back to get a refund tomorrow. I will also call Innova and find out what's up with the 3120 as you recommend. I continued doing DMM testing today with the following results for the Opti wiring:
Grey harness near manifold:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.89 V
Wire D: 0.06 V
Wire harness that plugs into the Opti:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.90 V
Wire D: 0.06 V
I read on another poster's thread that the GM manual states anything over 4.6v on wire A and B denotes a bad PCM. Can anyone verify this?
On ICM connector:
Wire A to ground C: 0.03 V
Wire D to ground C: 0.04 V
Wire B (white) to ground: 0.01 ACV with the motor being cranked with the key in ignition.
I'm trying to understand how the circuit flows. Does it go from PCM to Opti, then Opti on to the Coil and ICM?
The main questions i have from the above tests are:
1) Does the 5.xx V on wire A and B on Opti harness and connector indicate a bad PCM?
2) Why do I have no Voltage on the ICM wiring, both when plugged in and disconnected from the ICM?
3) How does the circuit flow? Does it go from PCM to Opti, then Opti on to the Coil and ICM?
Grey harness near manifold:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.89 V
Wire D: 0.06 V
Wire harness that plugs into the Opti:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.90 V
Wire D: 0.06 V
I read on another poster's thread that the GM manual states anything over 4.6v on wire A and B denotes a bad PCM. Can anyone verify this?
On ICM connector:
Wire A to ground C: 0.03 V
Wire D to ground C: 0.04 V
Wire B (white) to ground: 0.01 ACV with the motor being cranked with the key in ignition.
I'm trying to understand how the circuit flows. Does it go from PCM to Opti, then Opti on to the Coil and ICM?
The main questions i have from the above tests are:
1) Does the 5.xx V on wire A and B on Opti harness and connector indicate a bad PCM?
2) Why do I have no Voltage on the ICM wiring, both when plugged in and disconnected from the ICM?
3) How does the circuit flow? Does it go from PCM to Opti, then Opti on to the Coil and ICM?
Last edited by foxbat; Apr 4, 2009 at 11:33 PM.
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From: Hell was full so they sent me to NJ
Look at Shoebox's wiring diagram, sheet "pcm3". It shows the Opti, ICM and coil with complete circuitry, at the bottom of the page. The high ("B") and low ("A") res pulse patterns go to the PCM, to tell it the cam position. Knowing the cam position, the PCM determines when to fire the injectors (94 and up only - full sequential) and the igntion. The signal from the PCM goes to the ICM to fire the coil (white wire from pin B5 to ICM "B").
Shoebox also has the PCM pinouts, with the voltage for each pin (Connector B is on "pcm conn b"). The high and low res signals are shown as 0 or 5 volts, which I believe Speedy has already exlpained. I've never heard that anything over 4.6V represents a faulty PCM. The PCM sends 12V to the optical module ("C"). The optical module generates either a 0V or a 5V signal for the high and low res pulses, depending on whether the light is passing through the slot in the optical wheel. The output is a square wave. You could turn the engine slowly and see if the signal on A and B vary between 0 and 5V as they are supposed to. The low res will vary 4 cycles per crank rev, the high res will vary 180 cycles per crank rev. You could also read the frequency if your DMM has a frequency capability. The frequency will be 4X the RPM for the low res, and 180X the RPM for the high res.
OR..... you could just read the codes. The PCM will set a code for loss of either the high or low res pulse pattern.
Shoebox also has the PCM pinouts, with the voltage for each pin (Connector B is on "pcm conn b"). The high and low res signals are shown as 0 or 5 volts, which I believe Speedy has already exlpained. I've never heard that anything over 4.6V represents a faulty PCM. The PCM sends 12V to the optical module ("C"). The optical module generates either a 0V or a 5V signal for the high and low res pulses, depending on whether the light is passing through the slot in the optical wheel. The output is a square wave. You could turn the engine slowly and see if the signal on A and B vary between 0 and 5V as they are supposed to. The low res will vary 4 cycles per crank rev, the high res will vary 180 cycles per crank rev. You could also read the frequency if your DMM has a frequency capability. The frequency will be 4X the RPM for the low res, and 180X the RPM for the high res.
OR..... you could just read the codes. The PCM will set a code for loss of either the high or low res pulse pattern.
Thread Starter
Registered User
Joined: Jun 2001
Posts: 545
From: Tampa
Look at Shoebox's wiring diagram, sheet "pcm3". It shows the Opti, ICM and coil with complete circuitry, at the bottom of the page. The high ("B") and low ("A") res pulse patterns go to the PCM, to tell it the cam position. Knowing the cam position, the PCM determines when to fire the injectors (94 and up only - full sequential) and the igntion. The signal from the PCM goes to the ICM to fire the coil (white wire from pin B5 to ICM "B").
Shoebox also has the PCM pinouts, with the voltage for each pin (Connector B is on "pcm conn b"). The high and low res signals are shown as 0 or 5 volts, which I believe Speedy has already exlpained. I've never heard that anything over 4.6V represents a faulty PCM. The PCM sends 12V to the optical module ("C"). The optical module generates either a 0V or a 5V signal for the high and low res pulses, depending on whether the light is passing through the slot in the optical wheel. The output is a square wave. You could turn the engine slowly and see if the signal on A and B vary between 0 and 5V as they are supposed to. The low res will vary 4 cycles per crank rev, the high res will vary 180 cycles per crank rev. You could also read the frequency if your DMM has a frequency capability. The frequency will be 4X the RPM for the low res, and 180X the RPM for the high res.
OR..... you could just read the codes. The PCM will set a code for loss of either the high or low res pulse pattern.
Shoebox also has the PCM pinouts, with the voltage for each pin (Connector B is on "pcm conn b"). The high and low res signals are shown as 0 or 5 volts, which I believe Speedy has already exlpained. I've never heard that anything over 4.6V represents a faulty PCM. The PCM sends 12V to the optical module ("C"). The optical module generates either a 0V or a 5V signal for the high and low res pulses, depending on whether the light is passing through the slot in the optical wheel. The output is a square wave. You could turn the engine slowly and see if the signal on A and B vary between 0 and 5V as they are supposed to. The low res will vary 4 cycles per crank rev, the high res will vary 180 cycles per crank rev. You could also read the frequency if your DMM has a frequency capability. The frequency will be 4X the RPM for the low res, and 180X the RPM for the high res.
OR..... you could just read the codes. The PCM will set a code for loss of either the high or low res pulse pattern.
Now since the PCM is sending signal to wire B on the ICM connector to fire the coil, I do not have between 1-4 volts there while the car was being key-cranked. Had much less..almost nothing. Should I check the B5 white wire at the PCM under same conditions (cranking) to verify 1-4 volts at PCM, or does lack of 1-4 volts at the B ICM connector = bad coil, bad opti, or bad ICM ?
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Thanks Fred. I'll be taking the Actron back to get a refund tomorrow. I will also call Innova and find out what's up with the 3120 as you recommend. I continued doing DMM testing today with the following results for the Opti wiring:
Grey harness near manifold:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.89 V
Wire D: 0.06 V
Wire harness that plugs into the Opti:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.90 V
Wire D: 0.06 V
I read on another poster's thread that the GM manual states anything over 4.6v on wire A and B denotes a bad PCM. Can anyone verify this?
On ICM connector:
Wire A to ground C: 0.03 V
Wire D to ground C: 0.04 V
Wire B (white) to ground: 0.01 ACV with the motor being cranked with the key in ignition.
I'm trying to understand how the circuit flows. Does it go from PCM to Opti, then Opti on to the Coil and ICM?
The main questions i have from the above tests are:
1) Does the 5.xx V on wire A and B on Opti harness and connector indicate a bad PCM?
2) Why do I have no Voltage on the ICM wiring, both when plugged in and disconnected from the ICM?
3) How does the circuit flow? Does it go from PCM to Opti, then Opti on to the Coil and ICM?
Grey harness near manifold:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.89 V
Wire D: 0.06 V
Wire harness that plugs into the Opti:
Wire A : 5.04 V
Wire B: 5.03 V
Wire C: 11.90 V
Wire D: 0.06 V
I read on another poster's thread that the GM manual states anything over 4.6v on wire A and B denotes a bad PCM. Can anyone verify this?
On ICM connector:
Wire A to ground C: 0.03 V
Wire D to ground C: 0.04 V
Wire B (white) to ground: 0.01 ACV with the motor being cranked with the key in ignition.
I'm trying to understand how the circuit flows. Does it go from PCM to Opti, then Opti on to the Coil and ICM?
The main questions i have from the above tests are:
1) Does the 5.xx V on wire A and B on Opti harness and connector indicate a bad PCM?
2) Why do I have no Voltage on the ICM wiring, both when plugged in and disconnected from the ICM?
3) How does the circuit flow? Does it go from PCM to Opti, then Opti on to the Coil and ICM?
Thanks. I'm getting a clearer picture now. Sounds like the info I read about 4.6v on A/B = bad PCM is bogus, and clearly the wiring is ok between the PCM and Opti.
Now since the PCM is sending signal to wire B on the ICM connector to fire the coil, I do not have between 1-4 volts there while the car was being key-cranked. Had much less..almost nothing. Should I check the B5 white wire at the PCM under same conditions (cranking) to verify 1-4 volts at PCM, or does lack of 1-4 volts at the B ICM connector = bad coil, bad opti, or bad ICM ?
Now since the PCM is sending signal to wire B on the ICM connector to fire the coil, I do not have between 1-4 volts there while the car was being key-cranked. Had much less..almost nothing. Should I check the B5 white wire at the PCM under same conditions (cranking) to verify 1-4 volts at PCM, or does lack of 1-4 volts at the B ICM connector = bad coil, bad opti, or bad ICM ?
Why are you doing all this?
I didn't see one place in the all the previous pages where you said you checked even one plug for spark????????
Thread Starter
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Joined: Jun 2001
Posts: 545
From: Tampa
Per Haynes: tested battery voltage to coil (pink wire) 0.00 V
Tested primary resistance on both coil slots with the OHM scale: went as high as 16.XX.
Tested secondary resistance on high OHMS: -1
Where does the coil get 12v from? Via the ICM? Not sure how to test ICM? Is this sounding like an ICM Coil problem vs Opti?
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Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
What about the other cylinders? Why is this like pulling teeth????????
Its very clearly shown on the wiring diagram I referenced.... pink wire from a fuse in the U/H fuse box to the coil. DID YOU EVEN LOOK AT THE WIRING DIAGRAM????
The PCM sets codes for the ICM and the Opti. CHECK THE CODES!!!!!
Both the ICM and the Opti optical will show problems due to heat soak if they are failing.
Where does the coil get 12v from? Via the ICM?
Not sure how to test ICM? Is this sounding like an ICM Coil problem vs Opti?
Both the ICM and the Opti optical will show problems due to heat soak if they are failing.
Thread Starter
Registered User
Joined: Jun 2001
Posts: 545
From: Tampa
What about the other cylinders? Why is this like pulling teeth????????
Its very clearly shown on the wiring diagram I referenced.... pink wire from a fuse in the U/H fuse box to the coil. DID YOU EVEN LOOK AT THE WIRING DIAGRAM????
The PCM sets codes for the ICM and the Opti. CHECK THE CODES!!!!!
Both the ICM and the Opti optical will show problems due to heat soak if they are failing.
Its very clearly shown on the wiring diagram I referenced.... pink wire from a fuse in the U/H fuse box to the coil. DID YOU EVEN LOOK AT THE WIRING DIAGRAM????
The PCM sets codes for the ICM and the Opti. CHECK THE CODES!!!!!
Both the ICM and the Opti optical will show problems due to heat soak if they are failing.
Fred, I was not aware of having to check all cylinders for spark and I did look at the diagram, but I did not see arrows pointing to the direction of electricity travel. Also, I am aware you have advised me to check codes several times but I have tried that with no success via my Innova (unable to read PCM) and Actron which you noted was no good for my car. My laptop has Vista so I'm having problems operating Freescan.
I'll follow up on this stumble issue next week after new wires.
Thanks.
Thread Starter
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Joined: Jun 2001
Posts: 545
From: Tampa
Update:
Agter replacing the ignition fuse last week the car started. I replaced the two burnt plug wires today and it's back to not starting again. The start/no start thing has been going on for a while. Ign fuse is good. here's some new testing info:
1) Got the Innova to read my PCM after talking to tech support: no DTC's found
2) Tested for spark: at first no spark while cranking, then it started with one wire disconnected while testing spark.
3) ICM connector (connected): A,D 12v, C 2.65 ACV while cranking. ICM harness disconnected: A,D 12V, C up to 5.5 ACV while cranking.
4) Coil pink wire: 12V
5) Put on a spare coil - no change - no start
6) Had Autozone test the ICM: passed all tests
Looks like the coil and ICM are not at fault. Voltages on all wires look normal except 5.5 ACV on the ICM while cranking with connector off. I'm not sure what to do next. I have a new Delphi Opti on standby, but I'm not sure if it's a bad opti with no DTC, harnesses and voltages all seem normal?
Agter replacing the ignition fuse last week the car started. I replaced the two burnt plug wires today and it's back to not starting again. The start/no start thing has been going on for a while. Ign fuse is good. here's some new testing info:
1) Got the Innova to read my PCM after talking to tech support: no DTC's found
2) Tested for spark: at first no spark while cranking, then it started with one wire disconnected while testing spark.
3) ICM connector (connected): A,D 12v, C 2.65 ACV while cranking. ICM harness disconnected: A,D 12V, C up to 5.5 ACV while cranking.
4) Coil pink wire: 12V
5) Put on a spare coil - no change - no start
6) Had Autozone test the ICM: passed all tests
Looks like the coil and ICM are not at fault. Voltages on all wires look normal except 5.5 ACV on the ICM while cranking with connector off. I'm not sure what to do next. I have a new Delphi Opti on standby, but I'm not sure if it's a bad opti with no DTC, harnesses and voltages all seem normal?
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Posts: 545
From: Tampa
I have spark at the coil.
I was getting ready to take off the harmonic balancer this morning so I had to tap on it lightly with a rubber mallet. I tried starting again it came to life. Shut it off, and it struggled again before firing up. It's been doing this on and off today, but it starting eventually after a couple cranks.
I tested fuel pressure again both KOEO (39-40 psi) and with motor idling (no load 36-37 psi) and in 2nd gear under 'load' with wheels chocked and handbrake engaged and clutch partially up (36-38 psi) needle trembling a bit, but no less than 35psi. Unplugged the FPR vacuum line at idle: 45psi. Did a WOT rev in the driveway: steady 35-36psi. My gauge hose is not long enough to tape on the windshield for an actual WOT street run.
I was getting ready to take off the harmonic balancer this morning so I had to tap on it lightly with a rubber mallet. I tried starting again it came to life. Shut it off, and it struggled again before firing up. It's been doing this on and off today, but it starting eventually after a couple cranks.
I tested fuel pressure again both KOEO (39-40 psi) and with motor idling (no load 36-37 psi) and in 2nd gear under 'load' with wheels chocked and handbrake engaged and clutch partially up (36-38 psi) needle trembling a bit, but no less than 35psi. Unplugged the FPR vacuum line at idle: 45psi. Did a WOT rev in the driveway: steady 35-36psi. My gauge hose is not long enough to tape on the windshield for an actual WOT street run.