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Discussion Starter #1
Recently bought a 1995 GMC K2500 6.5 and I am having cold starting issues.

On a cold start I have no WTS light on the dash and have to crank the motor for 10-20 seconds before it will fire, it will then catch and idle rough for a few seconds before settling out to a very smooth idle.

On hot starts, I still have no WTS light, but the engine starts like a dream.

I have constant 12V to the hot side of the glow plug controller, but I am not getting any voltage on the load side to the glow plugs themselves. I removed the control connector and have 12V with the key in the run position on the red wire. Black wire has a good ground (0 ohms). The yellow wire (from the ecm) shows roughly 50 millivolts with the key in the run position. I do not know if this is the correct signal voltage here or not.

I am new to diesels but have some electrical background and it would seem to me that the glow plug controller has failed. But before I spend the money on a new part I would like to make sure that I am replacing the right part.

Any help is appreciated.

I should mention that the previous owner had replaced the glow plugs in the last 6 months and said the light just stopped coming on one day. Upon inspecting the controller I found the load side (GP side) connections to be loose, I have since snugged them up but to no avail.
 

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Welcome to DieselPlace
Here is a "No wait to Start" thread that will be helpful:

If you need to replace your glow plug controller, replace it with AC/Delco #212-366 only.
Aftermarket electrical parts will bring unwanted gremlins...
 
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The PCM will activate the GPR for 5 to 10 seconds when the key is turned on, it may cycle a few times, then quit.
You need to check the YELLOW wire on the GPR connector ( disconnected) for 12v. batt. as the key is turned on.
If yes then the GPR is probably bad, if no then the wiring or PCM may be the problem.
There is a GLOW fuse in the underhood fuse box, it is where the WTS lamp voltage comes from and is there to protect the WTS lamp and the PCM from the glow plug circuit. Make sure that fuse is good.
 
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Discussion Starter #5
Okay had another look at it this afternoon, and after reading the other thread and a few others, I decided to clean all of my grounds, while I am sure this was beneficial, it has not solved my problem.

Glagulator, I probed my glow plug connector again to confirm, and as before I am 12V on red with the key on, but only approximately 50 mV on yellow. Double checked the glow fuse, it is good, and for good measure checked all in the box under the hood, no issues with any of them.

One thing I noticed while cleaning my chassis ground is that the small black wire on my starter is very loose. I tried to snug it up, but I am going to have to drop the starter in order to do so, and haven't had he time yet. Could this be causing my issue?

OkDually thanks for the part number, I just had a bad experience with an aftermarket IAC on our Ford Explorer, it definitely pays to have the proper parts when they're needed, I will definitely be using the AC Delco if/when I replace it.

I will try to get to the diagnostic questionnaire when I have a moment, but trying to get all this done with 3 young kids wanting to help can be a little bit interesting lol.

When I get a minute I will check continuity in the yellow wire back to the ecm to ensure it is okay, I'm also going to check all glows and related wiring for ground shorts
 

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Did you measure the voltage at the YELLOW wire just as the key is turned on?
BTW, the 12v. ign. wire on the GPR connector is PINK, probably discolored.
Disconnect the 32 pin PINK connector on the PCM and the GPR conn. when you check for continuity and possible short to ground or another ciruit.
 
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Pink 32 pin PCM conn. in out.
 

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