Confusing p1371 code.
09-20-2021, 08:30 PM
#16
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Join Date: Apr 2021
Posts: 31
Re: Confusing p1371 code.
Not sure which one is the white wire because my ICM harness has been replaced and they're all different colors than OEM. Pins A and D checked out fine at 11.8 DC volts. Pin C read 0.0 ohms. Pin B was the only parameter that was off. I thought the pulse that the PCM sent was based off of the High and Low res signals that the optical sensor sent out?
09-21-2021, 01:03 AM
#17
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Re: Confusing p1371 code.
Pin B is the white wire (circuit 423). From PCM connector C2 pin 5:
http://shbox.com/1/1996_ec_03_ign_system.jpg
The PCM needs to know which cylinder is approaching TDC. It knows this based in the width (duration) of the low resolution pulse from the Opti. It knows the width of the low res pulse by counting the number of 1° high res pulses between the leading edge of the low res pulse to the trailing edge of the low res pulse. Four of the cylinders have a unique variable width pulse ranging from 7° to 22° wide. These four variable width pulses alternate with four equal 2° width pulses for the other cylinders.
Then, the PCM uses the timing tables (RPM on one axis, MAP on the other axis) to determine how many degrees in advance of TDC the spark (or the injector pulse) should occur. At exactly the right time the PCM sends a 5 volt pulse to the ICM to fire the correct plug, based on the position of the Opti rotor. The PCM is not simply picking a pulse out of the Opti's low res or high res stream, and forwarding it to the ICM. The PCM sends it own pulse to the ICM, and opens the injector with its own ground pulse. The source is a 5-volt regulated power supply in the PCM.
I use only the optical sensor in an OEM vented Opti to feed the cam/pseudo-crank position data to a MoTeC M48Pro engine management system, with an IEX 8-channel ignition module, driving 8 LS1 coils in direct fire. Works the same way. The MoTeC adds additional options on injector timing, allowing the injector pulse to be based on the leading edge of the Opti low res pulse, or the trailing edge of the low res pulse, and can calculate the start of the injector pulse by using “start of event” calculation, or back-calculating using an “end of event” basis. This helps coordinate the injection pulse width with the intake valve opening to prevent fuel from impinging on a closed valve, when possible. It's complicated.
http://shbox.com/1/1996_ec_03_ign_system.jpg
The PCM needs to know which cylinder is approaching TDC. It knows this based in the width (duration) of the low resolution pulse from the Opti. It knows the width of the low res pulse by counting the number of 1° high res pulses between the leading edge of the low res pulse to the trailing edge of the low res pulse. Four of the cylinders have a unique variable width pulse ranging from 7° to 22° wide. These four variable width pulses alternate with four equal 2° width pulses for the other cylinders.
Then, the PCM uses the timing tables (RPM on one axis, MAP on the other axis) to determine how many degrees in advance of TDC the spark (or the injector pulse) should occur. At exactly the right time the PCM sends a 5 volt pulse to the ICM to fire the correct plug, based on the position of the Opti rotor. The PCM is not simply picking a pulse out of the Opti's low res or high res stream, and forwarding it to the ICM. The PCM sends it own pulse to the ICM, and opens the injector with its own ground pulse. The source is a 5-volt regulated power supply in the PCM.
I use only the optical sensor in an OEM vented Opti to feed the cam/pseudo-crank position data to a MoTeC M48Pro engine management system, with an IEX 8-channel ignition module, driving 8 LS1 coils in direct fire. Works the same way. The MoTeC adds additional options on injector timing, allowing the injector pulse to be based on the leading edge of the Opti low res pulse, or the trailing edge of the low res pulse, and can calculate the start of the injector pulse by using “start of event” calculation, or back-calculating using an “end of event” basis. This helps coordinate the injection pulse width with the intake valve opening to prevent fuel from impinging on a closed valve, when possible. It's complicated.
09-21-2021, 02:37 AM
#18
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Join Date: Jul 2019
Location: Duvall, WA
Posts: 184
Re: Confusing p1371 code.
Saw this a couple days ago. My opti is aftermarket(Spectra) so would he be able to rebuild it even though it doesn't have the Mitsu sensor? And if so would this be a better alternative to buying a Summit Opti? Because it seems like those are my only two options at this point.
09-21-2021, 11:53 AM
#19
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Join Date: Apr 2021
Posts: 31
Re: Confusing p1371 code.
Pin B is the white wire (circuit 423). From PCM connector C2 pin 5:
http://shbox.com/1/1996_ec_03_ign_system.jpg
The PCM needs to know which cylinder is approaching TDC. It knows this based in the width (duration) of the low resolution pulse from the Opti. It knows the width of the low res pulse by counting the number of 1° high res pulses between the leading edge of the low res pulse to the trailing edge of the low res pulse. Four of the cylinders have a unique variable width pulse ranging from 7° to 22° wide. These four variable width pulses alternate with four equal 2° width pulses for the other cylinders.
Then, the PCM uses the timing tables (RPM on one axis, MAP on the other axis) to determine how many degrees in advance of TDC the spark (or the injector pulse) should occur. At exactly the right time the PCM sends a 5 volt pulse to the ICM to fire the correct plug, based on the position of the Opti rotor. The PCM is not simply picking a pulse out of the Opti's low res or high res stream, and forwarding it to the ICM. The PCM sends it own pulse to the ICM, and opens the injector with its own ground pulse. The source is a 5-volt regulated power supply in the PCM.
I use only the optical sensor in an OEM vented Opti to feed the cam/pseudo-crank position data to a MoTeC M48Pro engine management system, with an IEX 8-channel ignition module, driving 8 LS1 coils in direct fire. Works the same way. The MoTeC adds additional options on injector timing, allowing the injector pulse to be based on the leading edge of the Opti low res pulse, or the trailing edge of the low res pulse, and can calculate the start of the injector pulse by using “start of event” calculation, or back-calculating using an “end of event” basis. This helps coordinate the injection pulse width with the intake valve opening to prevent fuel from impinging on a closed valve, when possible. It's complicated.
http://shbox.com/1/1996_ec_03_ign_system.jpg
The PCM needs to know which cylinder is approaching TDC. It knows this based in the width (duration) of the low resolution pulse from the Opti. It knows the width of the low res pulse by counting the number of 1° high res pulses between the leading edge of the low res pulse to the trailing edge of the low res pulse. Four of the cylinders have a unique variable width pulse ranging from 7° to 22° wide. These four variable width pulses alternate with four equal 2° width pulses for the other cylinders.
Then, the PCM uses the timing tables (RPM on one axis, MAP on the other axis) to determine how many degrees in advance of TDC the spark (or the injector pulse) should occur. At exactly the right time the PCM sends a 5 volt pulse to the ICM to fire the correct plug, based on the position of the Opti rotor. The PCM is not simply picking a pulse out of the Opti's low res or high res stream, and forwarding it to the ICM. The PCM sends it own pulse to the ICM, and opens the injector with its own ground pulse. The source is a 5-volt regulated power supply in the PCM.
I use only the optical sensor in an OEM vented Opti to feed the cam/pseudo-crank position data to a MoTeC M48Pro engine management system, with an IEX 8-channel ignition module, driving 8 LS1 coils in direct fire. Works the same way. The MoTeC adds additional options on injector timing, allowing the injector pulse to be based on the leading edge of the Opti low res pulse, or the trailing edge of the low res pulse, and can calculate the start of the injector pulse by using “start of event” calculation, or back-calculating using an “end of event” basis. This helps coordinate the injection pulse width with the intake valve opening to prevent fuel from impinging on a closed valve, when possible. It's complicated.
09-21-2021, 12:50 PM
#21
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: Confusing p1371 code.
I'll try this one more time.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
09-21-2021, 01:04 PM
#22
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Thread Starter
Join Date: Apr 2021
Posts: 31
Re: Confusing p1371 code.
I'll try this one more time.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
09-21-2021, 02:26 PM
#23
Registered User
Thread Starter
Join Date: Apr 2021
Posts: 31
Re: Confusing p1371 code.
I'll try this one more time.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
The PCM uses the “timing” of the Opti pulses. The voltage of the signal from the Opti, or even the exact shape of the “square wave” pulse is not important, as long as there is a clearly defined beginning and end to the pulse. You aren't going to get a weak (low voltage) pulse sent from the PCM to the ICM because the pulse from the Opti to the PCM is “weak”, or because a pulse was missing from the Opti signal.
Why did you not get at least 1.0 volts on the white wire? Could be:
- corroded or damaged white wire, or connector pins
- poor ground at the ICM
- faulty voltage from the PCM regulated source
- short in the ICM
- meter or user error
Probably other possibilities, but that's all I can think of for now.
Try using the DC voltage scale on the meter. That is what the factory service manual instructions indicate for P1361- IC Voltage Low. Might want to look up that code in the manual for additional help. The digital volt meter specified in the FSM apparently has the ability to recorded the high and low DC voltage encountered during the test.
09-21-2021, 07:26 PM
#24
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: Confusing p1371 code.
Did you need to cut skin the white wire because the connector was still on the ICM? But you cut the white so it was no longer connected to the connector? Was this to see if the voltage loss was in the connector? Were all your tests done with the connector off the ICM?
09-21-2021, 07:31 PM
#25
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Join Date: Apr 2021
Posts: 31
Re: Confusing p1371 code.
Sorry if my response was confusing. I cut the white wire on the ICM connector a few inches from Pin B and tested just the exposed wire, not on the connector itself. This was to eliminate the possibility of a corroded pin or something inside the connector. Yes the ICM connector testing has been done with the ICM unplugged but with the coil connected.. I have been following the Shoebox guide for most of the testing.
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