Swap Grounding Gremlins! Tips on SENSOR ground please

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robcuda

robcuda

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I've got a wire, Black with Light Blue Tracer, that I believe is the sensor ground. The single wire T's off at the manifold running to front and rear sensors. I'm not sure where the wire end came from. Because it's a colored wire I don't think it's a dedicated ground (ie the cruise has a dedicated solid black ground). Is it a ground that should feed back into the PCM? Thanks for any thoughts.
64 Cuda
Donor: 97 5.9 Van
Running stock EFI
 
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I would not guess. Obtain a diagram of just exactly what you have and duplicate it. Sensors on modern EFI are normally "grounded" (signal ground) an insulated conductor running clear back to the ECU connector, not grounded to the block or anything else.

Since you may NOT be running wiring in original positions, bear in mind:

The factory spent a LOT of time fighting and solving EMI/ RFI problems (electromagnetic, spikes, and radio frequency interference)

Sometimes you may have to shield wiring. This on small signal (sensor) cables is normally done with what is called a Faraday shield. The gist of this is that it is a shielded cable which is only grounded at ONE end--the end near the ECU usually

You can also do this--and it is done in fact, with such as telco/ ethernet cabling. You cut loose unused pairs in the cable and tie them to one ground only at the terminal point. Leave the opposite end "float.

Be careful "guessing" It does not take much to 'take out' expensive electronics
 
robcuda said:
I've got a wire, Black with Light Blue Tracer, that I believe is the sensor ground. The single wire T's off at the manifold running to front and rear sensors. I'm not sure where the wire end came from. Because it's a colored wire I don't think it's a dedicated ground (ie the cruise has a dedicated solid black ground). Is it a ground that should feed back into the PCM? Thanks for any thoughts.
64 Cuda
Donor: 97 5.9 Van
Running stock EFI
Click to expand...
UPDATE: I found a basic schematic at it shows the Black w/Light Bl
67Dart273 said:
I would not guess. Obtain a diagram of just exactly what you have and duplicate it. Sensors on modern EFI are normally "grounded" (signal ground) an insulated conductor running clear back to the ECU connector, not grounded to the block or anything else.

Since you may NOT be running wiring in original positions, bear in mind:

The factory spent a LOT of time fighting and solving EMI/ RFI problems (electromagnetic, spikes, and radio frequency interference)

Sometimes you may have to shield wiring. This on small signal (sensor) cables is normally done with what is called a Faraday shield. The gist of this is that it is a shielded cable which is only grounded at ONE end--the end near the ECU usually

You can also do this--and it is done in fact, with such as telco/ ethernet cabling. You cut loose unused pairs in the cable and tie them to one ground only at the terminal point. Leave the opposite end "float.

Be careful "guessing" It does not take much to 'take out' expensive electronics
Click to expand...
I appreciate your input! Update: I found a basic schematic and it shows the origin of the Black/Light Blue sensor wire, it is from the PDC. How is the PDC grounded in a stock application?
 
The black wire with light blue tracer grounds through PCM at connector 1, pin 4. It goes to some main engine sensors through splices without going through the PDC but also goes to other items like cruise control switch by going through the PDC.
The PDC itself has joint connectors that have some of the ground wires connecting together, basically, and the few actual ground connections go out the square connector, that has 43 pins, out to a couple grounds.
 
Bobzilla said:
The black wire with light blue tracer grounds through PCM at connector 1, pin 4. It goes to some main engine sensors through splices without going through the PDC but also goes to other items like cruise control switch by going through the PDC.
The PDC itself has joint connectors that have some of the ground wires connecting together, basically, and the few actual ground connections go out the square connector, that has 43 pins, out to a couple grounds.
Click to expand...
Thanks for the info!
Bobzilla said:
The black wire with light blue tracer grounds through PCM at connector 1, pin 4. It goes to some main engine sensors through splices without going through the PDC but also goes to other items like cruise control switch by going through the PDC.
The PDC itself has joint connectors that have some of the ground wires connecting together, basically, and the few actual ground connections go out the square connector, that has 43 pins, out to a couple grounds.
Click to expand...
Thank you Bobzilla, yep it's exactly where you described. Time to order a shop manual for this donor! I'm now tracking the same wire around the harness to determine why I have one cut/loose end of the sensor ground mentioned.
 
Bobzilla said:
The black wire with light blue tracer grounds through PCM at connector 1, pin 4. It goes to some main engine sensors through splices without going through the PDC but also goes to other items like cruise control switch by going through the PDC.
The PDC itself has joint connectors that have some of the ground wires connecting together, basically, and the few actual ground connections go out the square connector, that has 43 pins, out to a couple grounds.
Click to expand...
Bobzilla, until I get a good shop manual can you please tell me theoretically if I have one 'open end' sensor grd wire, can the sensors still operate properly? Or is it a ground 'loop' that the PCM must see a return for proper ground? In addition, can I simply ground this wire to the block or fender as a temporary solution?
 
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i have a 97 truck(br) fsm and as said above, almost every sensor ground is black/lt blue tracer. the location you give might be a clue but on which side of manifold? too many to guess. i have the cd fsm that was gotten off ebay.
 
robcuda said:
Bobzilla, until I get a good shop manual can you please tell me theoretically if I have one 'open end' sensor grd wire, can the sensors still operate properly? Or is it a ground 'loop' that the PCM must see a return for proper ground? In addition, can I simply ground this wire to the block or fender as a temporary solution?
Click to expand...
If the wire that is cut is the single wire going into the PCM, then all sensors using that ground will read out of range.
If the cut wire is for one sensor connection that may be missing, only that sensor will read out of range.
If you have the intake with sensors, check which connectors on your harness will connect to properly and mark those with masking tape. Then you’ll know if any are missing. It will make easier to tell what is missing. Maybe post a picture of the harness so we can see where that wire is.
 
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..........and pay attention to various terminology. Sometimes it differs, but there are signal grounds which are not truly grounds, but rather a "low side." And then there are static/ EMI / shielding grounds which may or may not float at one end, and do NOT carry current or signals, nor are they supposed to.
 
Bobzilla said:
If the wire that is cut is the single wire going into the PCM, then all sensors using that ground will read out of range.
If the cut wire is for one sensor connection that may be missing, only that sensor will read out of range.
If you have the intake with sensors, check which connectors on your harness will connect to properly and mark those with masking tape. Then you’ll know if any are missing. It will make easier to tell what is missing. Maybe post a picture of the harness so we can see where that wire is.
Click to expand...
I think I found the most plausible original location of the Sensor Ground. As seen in the pics, I think it was part of the Cruise ground (unused). If attached to this, then you can see the factory ground it was wrapped with. If this is the case, then I think I can ground this sensor wire to the fender as it should be "at the end of the line" of the sensor ground system. Any thoughts are appreciated!

harness.jpg


IMG_0109.jpg


IMG_0110.jpg
 
Do not connect that black and light blue wire to the body. It grounds through a "clean" ground at the PCM, connector 1 pin 4 as previously mentioned. Then you just need to make sure the PCM grounds go to good, solid grounds similar to what the donor van used. That one cut wire can be marked for now and taped back into the harness (not used) if it is proven to be for the cruise switch and you are not using it. In your picture the one on the right with letter A is connector number 1. This connector layout and most of the pin outs is the same between trucks, vans, Durango’s, and Dakotas.
 
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Bobzilla said:
Do not connect that black and light blue wire to the body. It grounds through a "clean" ground at the PCM, connector 1 pin 4 as previously mentioned. Then you just need to make sure the PCM grounds go to good, solid grounds similar to what the donor van used. That one cut wire can be marked for now and taped back into the harness (not used) if it is proven to be for the cruise switch and you are not using it. In your picture the one on the right with letter A is connector number 1. This connector layout and most of the pin outs is the same between trucks, vans, Durango’s, and Dakotas.
Click to expand...
Thanks so much for your help. I will take your advice and not connect. Yes my pcm is labeled abc but thanks for clarifying 123.
 
robcuda said:
I've got a wire, Black with Light Blue Tracer, that I believe is the sensor ground. The single wire T's off at the manifold running to front and rear sensors. I'm not sure where the wire end came from. Because it's a colored wire I don't think it's a dedicated ground (ie the cruise has a dedicated solid black ground). Is it a ground that should feed back into the PCM? Thanks for any thoughts.
64 Cuda
Donor: 97 5.9 Van
Running stock EFI
Click to expand...
What are you doing for a fuel pump and crank position sensor on your setup?
Thanks
John
 
jos51700 said:
What are you doing for a fuel pump and crank position sensor on your setup?
Thanks
John
Click to expand...
Tanks Inc tank, with a GPA2 pump, pressure regulator at engine, return line, running 46re so stock CPS.
 
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