GPCM and Glow Plugs

[RandyH]

I've been trying to isolate a glow plug problem, even bought a clamp on DC ammeter so I could check each bank individually. Amazing how the ammeter simplifies troubleshooting this system. From everything I've read, I should see about 35-45 amps per bank or about 10 amps per glow plug after it settles from the initial peak. My passenger side was pulling 36 amps (good) and my driver's side only about 19, so it appears I've got two glow plugs that are not drawing any current. Next I separated the gp harness connectors located on top of the valve covers and checked resistance to ground. All the glow plugs read around .9 ohms so should be good. So, it seems like either the GPCM or the wire harness from GPCM to valve cover connector has a problem for two of the cylinders. Does anyone know if the GPCM can fail just on two of the outputs or does it usually either work 100% on one side or is dead? I'm hoping to dig back in over the next few days starting with double-checking that the glow plugs are reading about 1 ohm and then do a continuity test from the valve cover connector back to the GPCM connector. Assuming these both check out, I would say it has to be the GPCM.

Am I missing anything here before I go spend the $135 for a new GPCM?

Thanks.

 

[DaveBen]

I would put a volt meter to each of the glow plug connectors to make sure you are getting voltage to each glow plug. If not then I would look at the GPCM. They just don't die (GPCM).

Dave

 

[RoyBoy]

The UVC connectors themselves can create low volt/amps.. at an individual GP.. beyond the connector.

In Time, Miles (Starts), the pins, connectors and wires, can get fowled, burnt & brittle.. under the VC ?

Kinda what Dave said ?

There's no UVC harness on the 6.0, Joe

Failures on the GPCM seem rare, but it would be possible if everything else checks out.

 

[BIG JOE]

Whoooops

My Bad.

 

[RandyH]

GPCM Follow-up

Okay, finally had some time (and warmer weather) to chase this some more today. I started by pulling both passenger and driver's side harnesses apart again where they sit on top of the valve covers. Re-checked the resistance of the glow plugs through the GP end of the harness and all 8 checked out at approx. 1 ohm.

Next, I reconnected the harnesses and then disconnected the green and black connectors from the GPCM to test continuity of the entire harness from the glow plugs to the GPCM. Pins 1, 2, 6 & 7 of each connector all checked out at approx. 1 ohm between the glow plugs and battery ground, so the entire harness checked out. I then verified I had battery voltage on pin 9 of the black connector.

With the GPCM connectors reinstalled, I measured the current draw on both banks with my inductive DC ammeter and got the same 36 amps I had before on the passenger side and to my surprise I got about the same this time on the driver's side where I originally was only getting about 19 amps.

I started the truck (cold) and could immediately notice the difference in how smooth the cold start was. Outside temp was about 34 degrees.

It appears that by disconnecting the GPCM connectors and reseating them or moving the harness around on the GPCM end, I cleaned up a connection (or two since I was missing two GP's worth of amperage).

I'll know for sure it's fixed when I see how it runs cold tomorrow morning and when I start it up to leave work after it sits all day tomorrow. Keeping my fingers crossed!

 

[DaveBen]

I would bet you got it. It should be fixed for a while.

Dave