How to ground PDC?

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robcuda

robcuda

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Hi guys, having problems with how vehicle is running so I am going back to grounds. Some on the forum have suggested tapping into the PDC and running a ground to the block. Any tips on what wire(s) I should tap into? 97 5.9 B3500 van donor. Thank you for any thoughts!

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About the only thing I'm aware of in the PDC that is "ground" is the ground side of the relay coils. That, really should be pretty non critical. Grounding for EFI and electronics can be a real PITA. This gets worse with stuff like trunk mount batteries. If you have a chopped up adapted system, I've no idea how to get you started You might do some research on some of the Holley or Megasquirt documents for generalities on this
 
Make sure your engine is grounded to the body. The only thing grounded in the pdc would be grounds to operate the relays.
 
Mike69cuda said:
Make sure your engine is grounded to the body. The only thing grounded in the pdc would be grounds to operate the relays.
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The engine is grounded to the body. There is no obvious ground wire in the PDC, would you say that the harness ground is essentially grounding the PDC?
 
Since it is plastic, it would have to ground through the harness. There is no case ground.

Looks like Del & I are simultaneously posting again. I am in great company!
 
Mike69cuda said:
Since it is plastic, it would have to ground through the harness. There is no case ground.

Looks like Del & I are simultaneously posting again. I am in great company!
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Yes Del is always a great help! I have the harness grounded to the firewall but am now questioning if the stock vehicle had harness grounded to back of head. Would this make a big difference? My sensors are not happy :(
 
If you have a big thick ground from the engine to the body, it shouldn’t matter, but grounds can be funny things. I have gotten multiple bad new sensors over the past few years.

Can you provide some detail on your problems?
 
Mike69cuda said:
If you have a big thick ground from the engine to the body, it shouldn’t matter, but grounds can be funny things. I have gotten multiple bad new sensors over the past few years.

Can you provide some detail on your problems?
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It's a stock efi swap other than fuel pump.
Battery in trunk- #1 ground and pos
Fuel reads steady on regulator when parked
Starts right up and runs well. But as soon as drive it a couple miles it would buck, trans wouldn't shift right, and would die as soon as a stopped.
-removed/cleaned TB
-replaced IAC with OEM
same problem.
-replaced TBS with Dorman
car drove GREAT for 5 miles, then bucking and unhappiness started back!
 
This is a real tough one because we/I/ they have no idea what has changed as in "what all changed" from factory to "now." If you can, get access to an original OEM manual, which in a roundabout way, will show the factory ground points. These originally were specific. Not only for DC current, but for noise suppression. "It just might be" that you have created some sort of ground current/ ground loop that can/ has damaged some sensor(s)

I would not concentrate on the PDC. It is far more likely that some cut harness has changed or eliminated ground paths for something related to the CPU or related sensors

Really without painstakingly comparing what is "now" against original documents, there is no way to tell
 
robcuda said:
Hi guys, having problems with how vehicle is running so I am going back to grounds. Some on the forum have suggested tapping into the PDC and running a ground to the block. Any tips on what wire(s) I should tap into? 97 5.9 B3500 van donor. Thank you for any thoughts!

View attachment 1715742720

View attachment 1715742721
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The PCM supplies a "clean" ground for the sensors. That is, the sensor grounds run back to the PCM itself, not to the PDC. The PCM gets it grounds from the harness grounding to the engine. This ground is usually at the front of the engine, between the water pump and power steering pump. This means the engine itself needs a really good solid connection to the negative post of the battery.
So, since you have a trunk mounted battery, did you ground the battery to the body or is there a negative cable running from the battery all the way to the engine itself?

Is it setting any trouble codes (DTC)? Do you have a data link connector wired in to check for DTCs? Is it losing fuel pressure when this happens before it actually stops running? What do you have for a fuel pump and where/how is the fuel pump grounded?
 
Bobzilla said:
The PCM supplies a "clean" ground for the sensors. That is, the sensor grounds run back to the PCM itself, not to the PDC. The PCM gets it grounds from the harness grounding to the engine. This ground is usually at the front of the engine, between the water pump and power steering pump. This means the engine itself needs a really good solid connection to the negative post of the battery.
So, since you have a trunk mounted battery, did you ground the battery to the body or is there a negative cable running from the battery all the way to the engine itself?

Is it setting any trouble codes (DTC)? Do you have a data link connector wired in to check for DTCs? Is it losing fuel pressure when this happens before it actually stops running? What do you have for a fuel pump and where/how is the fuel pump grounded?
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Thanks for pointing out that the harness goes to the engine rather than body! I have the battery grounded from the trunk to the rear of the passenger head with #1 guage for pos and neg. I was getting an evap code, nuetral safety code, and camshaft position. I manually did a fuel sync by small increments until I lost the camshaft position code.
I've got a tanks inc set up with their pump. I watch the pressure regulator gauge when it's in the garage and it's steady but I can't confirm this while driving. The fuel pump is grounded in the rear to the body. Any ideas!
 
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I ran a ground wire, 4ga, from battery negative to my ecu case. It’s an aluminum case jtec ecu from a 2001 ram.
 
Your problem was likely due to the cps code. The fuel sync on magnums is critical.
 
I did it because 1, I figured it was bolted to the body originally and I had my just laying there, and 2, I noticed it ran different when I set it on the trans while running on the run stand. The ecu supplies ground for many different sensors. It made sense in my head that it needed the case grounded.
 
TT5.9mag said:
I did it because 1, I figured it was bolted to the body originally and I had my just laying there, and 2, I noticed it ran different when I set it on the trans while running on the run stand. The ecu supplies ground for many different sensors. It made sense in my head that it needed the case grounded.
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Hey, that's awesome input. I will ground the case. My buddy said that my engine bay "looked like Bill Gates threw up in it!" so I'm gun shy of adding more wires, but of course I will :)
 
TT5.9mag said:
Yes. The manual says it has to be done on a scope.
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I've gotta get my cuda over to a guy with a Snap On Scanner. We'll set the sync and I'll report back. It could be a couple days at least so if you see me repost please chime in!
 
robcuda said:
I've gotta get my cuda over to a guy with a Snap On Scanner. We'll set the sync and I'll report back. It could be a couple days at least so if you see me repost please chime in!
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Will do. Good luck
 
robcuda said:
It's a stock efi swap other than fuel pump.
Battery in trunk- #1 ground and pos
Fuel reads steady on regulator when parked
Starts right up and runs well. But as soon as drive it a couple miles it would buck, trans wouldn't shift right, and would die as soon as a stopped.
-removed/cleaned TB
-replaced IAC with OEM
same problem.
-replaced TBS with Dorman
car drove GREAT for 5 miles, then bucking and unhappiness started back!
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Almost sounds like no signal from speed sensor. Going from memory here but mine did same thing on my first drive after the 5.9 swap into my Jeep.
 
Whyjay said:
Almost sounds like no signal from speed sensor. Going from memory here but mine did same thing on my first drive after the 5.9 swap into my Jeep.
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Thanks for the tip. I will double check my trans wires. Was your problem that the speed sensor was not hooked up or did you have a break in the line?
 
Whyjay said:
Almost sounds like no signal from speed sensor. Going from memory here but mine did same thing on my first drive after the 5.9 swap into my Jeep.
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This is correct for the trans shifting problems but should have no effect on how the engine runs.
 
This entire time I’ve been reading the title of the thread wrong. I read PDC as PCM, (powertrain control module, aka ECU). The PDC (power distribution center) is not externally grounded per se, all of the sensor ground and relay grounds are ganged in to JC-1 connector and must be routed to ground. At least in my 01 ram OBD2 PDC that’s what it’s labled as. Grounds will be black or black w/blue tracer. 97 may be different. Pic attached and JC-1 circled in red. I tied all of mine together and ran a dedicated 10ga ground direct to battery negative. Sorry for my confusion.
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TT5.9mag said:
This entire time I’ve been reading the title of the thread wrong. I read PDC as PCM, (powertrain control module, aka ECU). The PDC (power distribution center) is not externally grounded per se, all of the sensor ground and relay grounds are ganged in to JC-1 connector and must be routed to ground. At least in my 01 ram OBD2 PDC that’s what it’s labled as. Grounds will be black or black w/blue tracer. 97 may be different. Pic attached and JC-1 circled in red. I tied all of mine together and ran a dedicated 10ga ground direct to battery negative. Sorry for my confusion.
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No problemo at all, thanks for the new info. I guess I was correct in hearing about some grounding the PDC. However, it appears that it may be only with 2001 and newer. Take a look at pic below, my box is very different than yours, no JC-1 or similar. Would it be safe to say that I do not have a way to ground my box and I'm limited to the harness ground?

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I believe what we are seeing is the difference between OBD1 (yours) and OBD2 (mine). I have never looked at the manual for an OBD1 harness but those relays and the sensor grounds have to go to ground somewhere.
 
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