Hard start cold

[White Duramax]

Working on a LML that starts hard when its below 30 degrees out. It has a new glow plug controller, all glow plugs are good. I compared amp draw to another LML- it draws over 100 amps at key on, this truck is only drawing around 20 amps- checking with an amp clamp on the glow plug feed wire. I also noticed the intake heater doesn't seem to come on after start up as the voltage comes up above 14 right away, the other truck stays around 12 for a couple minutes. I checked coolant and intake temperature readings- they are correct. Any input? thanks

 

[KyleC4]

ECM sends message to GPCM for intake air heater operation. I guess since you know that the heater isn’t working properly to start there and correct that first. Below 40 degrees the intake air heater can run up to approximately 10 minutes. I guess since you have a good working intake air heater on your comparison truck is to disable it and see if it hard starts like the one you’re dealing with. Then you know for sure that’s your problem area.

 

[White Duramax]

I did some testing this morning at 25 degrees. LML that starts fine- glow plug draw at key on, 120 amps, drops to 80 amps then to 0. LML with problem only drawing 15 amps then to 0. I tested intake heater draw and it does not come on until engine starts so I don't think it has anything to do with the starting issue.

 

[Bdsankey]

I did some testing this morning at 25 degrees. LML that starts fine- glow plug draw at key on, 120 amps, drops to 80 amps then to 0. LML with problem only drawing 15 amps then to 0. I tested intake heater draw and it does not come on until engine starts so I don't think it has anything to do with the starting issue.

Have you tried swapping the glow plug controllers between the one with issues and the one you're verifying? Is the one with issues tuned? Is this a new issue or has the truck started hard previously?

 

[White Duramax]

I did take the controller off the truck with no issue and plug it in to the other one- same hard start. Both trucks are tuned. The truck with the issue has been tuned for years and never had a starting issue until the glow plug controller was replaced due to throwing a fault, thats what does not make sense. I'm going to go over wiring more.

 

[Bdsankey]

Have you compared the readings the truck gives in regards to ambient temp, coolant temp, intake air temp? I'm wondering if maybe one of those sensors is reading incorrectly and causing the truck to think its significantly warmer than it is?

All grounds good? Have you tried to unplug or swap the bad intake air heater into the known good working truck to see if the issue follows the symptom of the bad starting truck?

 

[White Duramax]

I have compared data, coolant, ambient, and intake temps are all really close on both trucks. Did not mess with the intake heater yet. I did check voltage at a glow plug and command glow plugs on, truck with problem is around .5 volt, other truck is 1.7 volt. Would like to know more about what controls the glow plug operation.

 

[zakkb787]

Just a thought and I could be wrong, but do the glow plug controllers not have to be programmed to the truck before they work properly?

 

[Bdsankey]

Just a thought and I could be wrong, but do the glow plug controllers not have to be programmed to the truck before they work properly?

I thought about this also.

 

[White Duramax]

I believe the only programming is the injector codes are stored in the gpcm.

 

[02greysixer]

I'll have to check tomorrow but I'm fairly sure lml glow plug modules are blank and must be programmed

Sent from my SM-G960U using Tapatalk

 

[White Duramax]

I checked and the injector codes were all blank, I copied them from the ecm to the gpcm. I let it sit outside and just tried to start it, same as before. Only other thing I can think of is to swap my ecm into it and see what happens.

 

[zakkb787]

https://www.duramaxdiesels.com/forum/showthread.php?t=79892

So you did what was described in this thread?

 

[White Duramax]

Yes, copied from ecm and programmed to gpcm with my Tech 2.

 

[White Duramax]

Can't swap LML ecms without reprogramming. Any other ideas?

 

[White Duramax]

I got the old gpcm from the guy and hooked it up, it starts perfect with it. He changed the gpcm due to a fault, not sure what the fault was. The part number on the old one is 12642260, I can't get this to cross to anything. The new gpcm part number is 12652113 which seems to be correct.

 

[Chevy1925]

quick google shows ebay selling a few of that old part number for 2012 Van LGH engine.

is this "LML" really in a van and not a truck? Vans are LGH engines with some variable differences.

 

[White Duramax]

It is a truck, LML engine. I've done some more research and I think the new gpcm has to be dealer programmed to work correctly, programmed besides the injector rates.

 

[02greysixer]

I forgot to post back in this. Glow plug controller does need programmed by dealer level tool and then flow rates copied in.

Sent from my SM-G960U using Tapatalk