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Discussion Starter · #1 ·
Before I get yelled at for not searching... I have tried to look for my answer.
I understand that the 3 wire is a hall effect sensor, and sends out a different signal than a 2 wire, later model sensor.

Here is my situation.

I just put a later model "u" code motor into my 97 (which was a vulcan motor to start). I and am having trouble with the CPS. The 97 i have has a three wire hall sensor. The newer motor has the 2 wire one. I used the 98+ wiring harness on the engine, and just hooked it into the wiring harness for the car.

My questions are:

1) Can I just change the black sensor up top, and somehow alter the wiring to work?

2) What wiring would I have to alter, and what is the best way to do that. I know the ECU is going to be looking for a specific signal, and with three wires instead of 2, I am wondering if you have to splice another wire into the main harness.

Please help.. need to finish car by in a few days.

Car is running, albeit rough, and throwing the p0340 code.
That is the only engine code being thrown, other than one related to the EVAP system, but I know what that is.
 

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Cake monster
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Before I get yelled at for not searching... I have tried to look for my answer.
I understand that the 3 wire is a hall effect sensor, and sends out a different signal than a 2 wire, later model sensor.

Here is my situation.

I just put a later model "u" code motor into my 97 (which was a vulcan motor to start). I and am having trouble with the CPS. The 97 i have has a three wire hall sensor. The newer motor has the 2 wire one. I used the 98+ wiring harness on the engine, and just hooked it into the wiring harness for the car.

My questions are:

1) Can I just change the black sensor up top, and somehow alter the wiring to work?

2) What wiring would I have to alter, and what is the best way to do that. I know the ECU is going to be looking for a specific signal, and with three wires instead of 2, I am wondering if you have to splice another wire into the main harness.

Please help.. need to finish car by in a few days.

Car is running, albeit rough, and throwing the p0340 code.
That is the only engine code being thrown, other than one related to the EVAP system, but I know what that is.
Why not just pull the CPS and install a new one with sensor for the right year? I would suggest getting a new one anyway, they fail really easily. Don't hack the wires together. The new one will have the 3 wires and will send the right signals to the PCM.
 

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Discussion Starter · #4 · (Edited)
Probably should have used the original wiring harness.
Well.. yeah... I know that now....:D

To the other point... That likely wont work. See... the engine harness is 2 wire. The ecu harness is expecting 3 wire signal. If I put a 3 wire sensor in the car, there is nothing for it to plug into. Only a 2 wire plug.

I am just trying to avoid changing harnesses out in the car. Really dont want to do that.


What I want to accomplish is a way to cut off the two wire plug, wire the three wire plug on, and make the necessary wiring modifications to get the signal through the 98+ engine harness to the 97 ECU and car harness.
 

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Cake monster
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Well.. yeah... I know that now....:D

To the other point... That likely wont work. See... the engine harness is 2 wire. The ecu harness is expecting 3 wire signal. If I put a 3 wire sensor in the car, there is nothing for it to plug into. Only a 2 wire plug.
Run a wire from the 3rd to where the harness connects possibly? I would probably just install the old harness in that case.
 

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Discussion Starter · #6 ·
Yeah, I just need to find out what the pinout on the harness is, and if all 3 wires go through.

Mainly, I need to know the pinout differences on the harness between the 2 wire and three wire.

Although, I suspect one of the three wires is a ground on the hall effect sensor. If that is true, I might get lucky and just be able to wire in the two, and then ground the third.

Anyone have wiring schematics for a 97 and, for instance, a 99 vulcan motor?
 

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Discussion Starter · #7 · (Edited)
Ok, found the 97 wiring schematics here... now all I need is the 98+

http://www.howtopdf.com/?_qdS3RxX


edit: Ok.. the black/white wire on the 3 wire is a ground.... getting closer. Anyone have the 98+?

edit-edit: The red appears to be a 12v hot... leaving only one wire for signal.

So, if one of the 2 wires on the 2 wire plug is a 12v hot wire, and the signal wire from the 2 wire goes to pin 85 on the harness, I am good to go.
 

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Discussion Starter · #8 ·
Ok, figured it out.

The two prong sensor sends the info on pin 85 to the ECM. It is then returned on pin 91.

The three prong sensor sends the info on pin 85, but since there is no return needed on a Hall effect sensor, it doesn't utilize one.

The three prong sensor has a ground, a 12v hot wire (on the same relay circuit as the ISC motor, and the signal wire.

THEREFORE, I should be able to ground the black/white wire to the chassis, provide power to the 12v via the red wire on the ISC, and wire the signal wire to the blue signal wire on the 2 prong plug, and leave the other return wire from the 2 prong unused. This should work fine.

Anyone see any problems with this?

Of course, I am using the whole synchronizer/sensor out of the 97 car.
 

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Discussion Starter · #9 ·
<resolved>

Wiring worked as i had posted. Red wire on 3 prong connector gets a 12v switched wire. Black/white gets a chassis ground. Blue wire gets the blue wire from the 2 prong sensor.

Other wire from 2 prong sensor goes unused.

Works like a charm, no more p0340 code.

So, no need to replace the entire harness... Just rewire.

Hope this helps someone else down the line.
 

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There were / are 2 types of CMP sensors used. One is a Hall effect switch sensor that has 3 wires.... +12V, ground, and signal out. The other is a VR (variable reluctance) sensor that operates similar to the ABS wheel sensors. Those are the 2 wire ones. The output signals from the 2 are completely different.
 
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