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Discussion Starter #1
Recently bought a 2003 Silverado 2500HD w/LB7, federal emissions.
This is my first GM vehicle and I'm realizing how crappy the electronics are. Nearly every switch and electrical component needs replacing. Maybe related, maybe not.
The truck has some sort of aftermarket tune, but I dont know what or how to tell.

I've replaced some things but the current status is:
- battery light faintly on sometimes
- high beam light on randomly (irrespective of truck being on or headlights being on)
- slow to crank
- glow light takes a long time. like 10+ seconds
- smokes some on cold start (less than before)
- glow rail on the drivers side is very warm/hot to touch, but the passenger side is cold.
- some moisture in cabin. I think the passenger door seal was leaking


Initially when I got it, it would crank over strong but would smoke a LOT on cold starts and had a very rough idle.
- I replaced all the glow plugs, and noticed some were covered in oil, not sure if that helped, they looked fairly new.
- It had a CEL for the air intake heater, I noticed it wasn't plugged in all the way so I fixed that and cleared the codes and that seems ok
- Replaced the FPR (what a pain in the ass) which seemed to help at first but hard to say.
- Replaced the glow plug relay pack, didn't seem to make a difference.
- Replaced the glow plug rails, no difference.
- Checked resistance of all the glow plugs, all are 0.8-0.9
- checked continuity of glow plug rail link wire (across the engine) and it has continuity. Seems like it would be a huge pain to replace if it was damaged or grounding out elsewhere.
 

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Discussion Starter #2
I guess I wrote a lot of words there.

Primary symptom I’m concerned with at the moment is:
When glowing, the drivers side glow rail is very hot to the touch but the passenger side one is cold to the touch. All the glow plugs are new...
 

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Recently bought a 2003 Silverado 2500HD w/LB7, federal emissions.
This is my first GM vehicle and I'm realizing how crappy the electronics are. Nearly every switch and electrical component needs replacing. Maybe related, maybe not.
The truck has some sort of aftermarket tune, but I dont know what or how to tell.

I've replaced some things but the current status is:
- battery light faintly on sometimes
Good chance this is the iffy charging system on the truck acting up. You may want to clean the battery terminals, pull them from the truck and trickle charge them, clean the grounds and alternator contacts and see if this helps with your issues. Its very common for the older GM trucks to have weird electrical issues when battery voltage is low, and the undersized charging cables dont do us any favors here.
- high beam light on randomly (irrespective of truck being on or headlights being on)
low battery voltage to the BCM can do some weird things, as can bad grounds. Theres 3 grounds i can think of to check, 1 under the driver side A pillar, 1 on the firewall to the back of the engine, and 1 from the cab to the frame under the driver seat. Clean them and see if the issue improves. You may also want to pull the fuses 1 at a time and see if theres corrosion built up on the blades or inside the terminals. A lot of cluster issues are actually just low voltage causing errors in the logic circuit.
- slow to crank
weak starter motor or low voltage, check the engine to frame grounds, and the 12V cable from the junction block to the starter as well as the relay contacts and the starter wire fuse contact. This could also be from low battery voltage.
- glow light takes a long time. like 10+ seconds
low voltage will make them take longer to warm up, but given the issue with the glow plug rails i would guess that you either have a short somewhere in the glow plug circuit, or the controllers failing, but it could also be voltage related, and since trying to fix that is generally free to little expense i would start there.
- smokes some on cold start (less than before)
what color smoke? white smoke indicates failing injectors / coolant in the exhaust, black smoke indicates too much fuel being shot into the engine and bluish grey smoke is burning oil.
- glow rail on the drivers side is very warm/hot to touch, but the passenger side is cold.
my guess would be a shorted plug or something like that on one side, you can carefully remove the nuts from the glow plugs and test each one with a multi meter on ohms. The stud to the block should have a few ohms of resistance, if its almost 0, or over 2 or so, that plug is probably bad and needs to be replaced. It could also be that the controller is not working right, this may contribute to your smoke at start and rough starts if its cold out and half the plugs arent working.
- some moisture in cabin. I think the passenger door seal was leaking
17 year old truck, id be surprised if there were no leaks anywhere. Does it have a sunroof? the drains for them are known to clog up and cause leaks into the cab. IIRC you would see that moisture around the A pillar, but i dont remember if its the driver side of passenger side.

Initially when I got it, it would crank over strong but would smoke a LOT on cold starts and had a very rough idle.
- I replaced all the glow plugs, and noticed some were covered in oil, not sure if that helped, they looked fairly new.
there should NOT be oil on the glow plugs. are you sure it was oil and not sluggy carbon mixed with some diesel residue or something?
- It had a CEL for the air intake heater, I noticed it wasn't plugged in all the way so I fixed that and cleared the codes and that seems ok
- Replaced the FPR (what a pain in the ass) which seemed to help at first but hard to say.
- Replaced the glow plug relay pack, didn't seem to make a difference.
- Replaced the glow plug rails, no difference.
- Checked resistance of all the glow plugs, all are 0.8-0.9
- checked continuity of glow plug rail link wire (across the engine) and it has continuity. Seems like it would be a huge pain to replace if it was damaged or grounding out elsewhere.
well that puts some holes in my glow plug thoughts. Replacing that wire would not be that bad if you just created a new run to tie the rails together. For one side to be getting hot and not the other there needs to be more current (and in this case, significantly more current) running through 1 rail than the other. Given how high the current is that were talking about, it would not take very much resistance in the form of corrosion on that link wire to cause a huge drop across that rail. So say the connector on 1 end was corroded a little, that extra .1-.2 ohms of drop is not much on a meter but given you have 4 glow plugs at 1 ohm or so in parallel for a total resistance of .25 ohms, that .1 - .2 is significant and is almost halving the current to the rail.


to start with on the electronics, besides power and ground distribution from the charging system, the trucks actually pretty well put together in terms of the vehicle electronics. Keep in mind that its a 17 year old truck thats been exposed to moisture every day of its life so likely contacts and terminals are building up some corrosion over the years, so its not unusual to see some switches and buttons not working.

I commented on your bullet points in the quote above for easier reading.
 

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I guess I wrote a lot of words there.

Primary symptom I’m concerned with at the moment is:
When glowing, the drivers side glow rail is very hot to the touch but the passenger side one is cold to the touch. All the glow plugs are new...
Also check the hot wire feeding the passenger side glow plugs, I believe the it's on the front of the drivers side rail and jumps over to the passenger side rail.
 

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Discussion Starter #5
Also check the hot wire feeding the passenger side glow plugs, I believe the it's on the front of the drivers side rail and jumps over to the passenger side rail.
my current theory is that wire has issues, just not sure what. The truck doesn't have any rust, and I've checked the ends of the wires to/from the glow plug rails and all the terminal connections look good.
I'm definitely getting continuity through that wire (tested with multimeter).

Does that wire, the glow plug crossover link, have a separate part number? Or is it just considered part of the engine wiring harness
 

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Discussion Starter #6
I guess I can't edit my posts but I found the part numbers for the glow rail wires:
- short one from controller to drivers side rail: 97224723
- long one over engine block between rails: 97224722 - DISCONTINUED of course :(
 
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