LBZ: glow plug delete

[07metallicgreen]

ive been reading about if you can or cannot delete the gpcm on a lbz. im taking my glow plugs out and I wanted to take the controller off too. if I cant can I still cut the wires going to the glow plugs and the power cable off, and leave the rest of the big plug?

 

[Muff]

What is your reasoning for removing the glow plugs?

 

[07metallicgreen]

Clean wires up, and I've heard of the tips breaking off. Plus I only drive it when it's warm, so I'm not really worried about it starting hard
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[DAVe3283]

I think the tips breaking off only really happens to the LB7 & LLY. That isn't something you really need to worry about, IMO.

This is coming from the proud owner of a LB7 where a tip did break off, then went through the #1 cylinder, destroying the head, valves, and piston. And I fully intend to put glow plugs back in when my build is done.

The important thing is don't over-tighten them! I'm positive that is why the tip snapped off (rammed the end of the plug into the head too hard). Torque specs are your friend :baby: (Also, get OEM or a high-quality part.)

If you are dead set on removing the glow plugs, and are willing to put up with the truck potentially being unusable on cold days (even in an emergency), I would think you could remove the whole module and just turn the codes off with EFILive. I would try just unplugging it and see if you can get the check engine light to go away. If so, then you can gut the harness.

The GPCM does hold injector flow rates, but only as a backup, IIRC. So if you swap ECUs, you won't be able to use EFILive to restore your flow rates. You'll need a Tech2.

Let us know how it goes! :thumb:

 

[JoshH]

I think the problem is that the CAN bus system (or whatever it's called) that the ECM/TCM talk on runs through the GPCM also. I think I read something about some sort of resistor might be able to complete the loop, but I've never tried it. If you want to leave the module and remove the wires for the glow plugs, that shouldn't be a problem. Just turn off the glow plug codes.

 

[07metallicgreen]

That's what I was thinking josh. Do you think I need to keep the power cable?
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[JoshH]

I don't see why you would need the power cable, but I couldn't say for sure.

 

[Harbin_22]

Not sure on LBZ but my LMM won't crank without the gpcm hooked up.

 

[DAVe3283]

I think the problem is that the CAN bus system (or whatever it's called) that the ECM/TCM talk on runs through the GPCM also. I think I read something about some sort of resistor might be able to complete the loop, but I've never tried it. If you want to leave the module and remove the wires for the glow plugs, that shouldn't be a problem. Just turn off the glow plug codes.

Oh, right, I forgot about the CAN bus. D'oh!

I found a document that says it is a 120 Ohm resistor for GMLAN, and it looks like the standard CAN interface is the same.

Not sure on LBZ but my LMM won't crank without the gpcm hooked up.

That same document says this is normal due to the missing terminating resistor.

It also looks like Delphi makes a plug-in resistor that you can jam in there, but really, a 120 Ohm resistor is cheap and should be at any Radio Shack or similar.

So you could figure out what pins in the GPCM connector are the CAN bus, and just stick a resistor across them. My service manuals only go to 2005, or I would look that up for you.

The other thing you can do is once you know the pins, measure the resistance across those 2 pins on the GPCM with a multimeter, and that would be the resistor you need. I bet it is 120 Ohm.

That would be an interesting test. If you try it, let us know either way.

 

[LBZGPCM]

Oh, right, I forgot about the CAN bus. D'oh!

I found a document that says it is a 120 Ohm resistor for GMLAN, and it looks like the standard CAN interface is the same.

That same document says this is normal due to the missing terminating resistor.

It also looks like Delphi makes a plug-in resistor that you can jam in there, but really, a 120 Ohm resistor is cheap and should be at any Radio Shack or similar.

So you could figure out what pins in the GPCM connector are the CAN bus, and just stick a resistor across them. My service manuals only go to 2005, or I would look that up for you.

The other thing you can do is once you know the pins, measure the resistance across those 2 pins on the GPCM with a multimeter, and that would be the resistor you need. I bet it is 120 Ohm.

That would be an interesting test. If you try it, let us know either way.

ZeroGravity58 did this, I want to do it...... How and what would I do to a LBZ GPCM to make this happen, can anyone help identify wires and I am not a wire guru, so there is that... But I can follow directions well... I suspect that my U0106 is a bad GPCM and Reduced Power Mode is the result, the 120ohm resistor is the probable communication problem and YOU CANT BUY A GPCM ANYWHERE NEW OR USED.... So, how would I test if a 120ohm can fix this, can you help identify what wires, where and what to do to them?

Thanks

 

[juddski88]

ZeroGravity58 did this, I want to do it...... How and what would I do to a LBZ GPCM to make this happen, can anyone help identify wires and I am not a wire guru, so there is that... But I can follow directions well... I suspect that my U0106 is a bad GPCM and Reduced Power Mode is the result, the 120ohm resistor is the probable communication problem and YOU CANT BUY A GPCM ANYWHERE NEW OR USED.... So, how would I test if a 120ohm can fix this, can you help identify what wires, where and what to do to them?

Thanks

You can get cheap diagrams on alldatadiy. You can get some free diagrams and pinouts on gmupfitter. You can get factory service info right from techline connect, as well as access to factory canbus diag software if you have a good pass through device

 

[DAVe3283]

Per Techline, pins 43 & 44 are the CAN bus. Stick a 120Ω resistor across those two pins and see if communications start working.

 

[LBZGPCM]

Per Techline, pins 43 & 44 are the CAN bus. Stick a 120Ω resistor across those two pins and see if communications start working.
View attachment 116244

I see there are 1/4w 1/2w 1watt, I am sure I need to choose a comparable 120ohm? Any thoughts?

OK, let me get a 120ohm and lets see who I send some gifts to for helping... I WILL GET BACK SOOOON....

 

[Stcked_lbz]

Sorry to wake up this thread again. Just going through the same process of gpcm delete and finding very limited info. Understand the 120 ohm resistor. Only question is I have a single wire running from the gpcm back to the main engine harness. That splices into another wire that runs to a plug right behind the ac compressor. Havent heard of anyone else talking about this so just curious. Would be happy to provide some pics if that helps. Thanks!

 

[ZeroGravity58]

It's been awhile since I did this. The only two wires you will be worried about it's the tan with black strip and tan with white strip if I remember right. Those are your canbus wires feeding the GPCM. Everything else can get stripped out of the harness. Your glowplug light will stay on so you will have to remove the bulb. I bought a water proof 120ohm resistor online and spliced it into the engine harness between the two can us wires.