Wire tap to body ground on APPS wire

[FosterW]

In the C1 connector on my PCM, the orange/black tracer wire that leads to the TPS has a wire tap connected to it leading to body ground. It is tapped a few inches out from the PCM. I am having no issues at this time, just curious if anyone knows what this is all about. It does not appear factory, and wiring diagram does not show that wire going to ground for any reason. 

 

02 automatic. 

[Mopar1973Man]

Remove that ground return to stock. 

 

Then test your alternator for excessive AC noise. Double check for noise filter on the PCM and remove.

 

Then do the W-T ground wire mod. 

Add on to that mod. 

 

[FosterW]

Thanks for the reply. I read through both of the modifications yesterday, and while doing some preliminary investigating noticed the wire tap I mentioned.  What it’s trying to be achieved with the wire tap I described? 

 

Additionally, what is the noise filter on the PCM? And what is the process to check for alternator AC noise? 

[Mopar1973Man]

7 hours ago, FosterW said:

What it’s trying to be achieved with the wire tap I described?

 

Attempting to clear the APPS of AC noise. Actually, it can cause issues or damage for the ECM. Sensor ground is NOT body ground.

 

7 hours ago, FosterW said:

Additionally, what is the noise filter on the PCM?

 

A noise filter for filtering out the AC noise getting into the PCM which typically does the 45 MPH hunting of the torque converter. 

 

7 hours ago, FosterW said:

And what is the process to check for alternator AC noise?

 

Measure the AC noise of the BATT terminal and body ground. 50mV AC is marginal 100mV AC is a fail. Like now with all the mods I'm down to as low as like 18mV AC. 

 

 

[IBMobile]

The chart for C1  at the PCM doesn't show an orange/black (OR/BK) wire but there is an orange/dark blue (OR/DB) wire at pin #23 used for the throttle position sensor signal.  May be this is the wire with the dark blue looking black.  

 

[Mopar1973Man]

Still, in all, there is absolutely no need for this mod adding a ground wire to the APPS sensor leads. 

 

Just remove that ground wire and repair the wire. Now test the alternator for excessive AC noise. If excessive AC noise is found replace the diode pack or replace the alternator. Now you'll want to do the W-T ground wire mod. Then for safety, you want to do my PCM protection mod as an add on. 

[FosterW]

Understood. So the WT ground wire mod eliminates the 140A alternator fuse at the PDC? Since it is suggested to run that wire straight to the passenger battery (+) ?

[Mopar1973Man]

Ok, there is an add on mod for the W-T ground wire. This answer that question.

 

 

 

[FosterW]

What is the gauge of the dark blue wire at pin 25 in C3?

 

The wiring guides in the articles do not list the wire gauges. 

[IBMobile]

All the wires at the PCM are 18 gauge EXCEPT  C1 pins #22 RD/WT,  # 31 and #32 BK/TN,  C3 pin #12 DG/OG; these are 14 gauge. 

[Mopar1973Man]

I used a standard ATC fuse holder and installed right near the PCM. You only needing a 5 amp fuse so gauge size is not a huge problem. Like my fuse holder is 16 AWG. At 15 feet, 5 amp load, 12 Volt system 16 AWG wire is suggested. But the run isn't that long even.