LB7: Hard/Rough Starts Cold

[Bdsankey]

Those 2 blue wires are feedback to the ECM. One is used to monitor glow plug voltage, the other is for the IAH voltage, both downstream from the relay. If you had both connected to the same terminal, it seems like the ECM may throw a code?

P0380 for the glow plugs, P0540/P0543 for the IAH.

It’s not setting a CEL, I’ll scan for codes with the V2 this morning to make sure.

Voltage seems low for just having the key on, as well as voltage to the glow plugs. I agree that the voltage drop across the glow plug wiring seems excessive too

Batteries are brand new, like I put them in on 1/11/2020 and used Interstate MTP-78DT. Keep in mind, they key on engine off voltage is with a FASS/glow plugs/intake air heater/HVAC/radio all running. I’m going to replace the controller and wiring to the flow plug rails. The bars between each glow plug don’t appear to be touching anything they shouldn’t leading me to believe one of the wires may have a potential short or got kinked/pinched etc since the passenger side resistance swings quite a bit.

 

[dndj]

Not as cold as you, about 50 degrees outside, but here's what I measured on my 03 with my trusty Fluke meter for comparison. My truck batteries are 4 years old.

Intake heater circuit at heater: 10.3v
At 12v input stud/lug for glow plug/IAH controller (relays) 10.6v
At output stud/lug for glow plugs, on the controller 10.3v
At glow plugs, driver's side, measured @ #6: 10.0v
Supply: 12.26v key off, 11.0v key on

Supply voltages look nearly identical key on/key off. The biggest difference I see is the voltage on your glow plug rail is significantly lower.

 

[Bdsankey]

Not as cold as you, about 50 degrees outside, but here's what I measured on my 03 with my trusty Fluke meter for comparison. My truck batteries are 4 years old.

Intake heater circuit at heater: 10.3v
At 12v input stud/lug for glow plug/IAH controller (relays) 10.6v
At output stud/lug for glow plugs, on the controller 10.3v
At glow plugs, driver's side, measured @ #6: 10.0v
Supply: 12.26v key off, 11.0v key on

Supply voltages look nearly identical key on/key off. The biggest difference I see is the voltage on your glow plug rail is significantly lower.

I'm thinking that is the problem. It doesn't help that on the way to work the truck decided to develop a rod knock.

 

[dndj]

I'm thinking that is the problem. It doesn't help that on the way to work the truck decided to develop a rod knock.

Bummer. That doesn't sound good.

I should have also mentioned my truck has 140k on it and glow plugs haven't been touched. I am not sure of the expected life on these, but maybe it's possible I have a few out, and thus my 10.0v voltage doesn't pull down as low as your 8.26v.

 

[Bdsankey]

Bummer. That doesn't sound good.

I should have also mentioned my truck has 140k on it and glow plugs haven't been touched. I am not sure of the expected life on these, but maybe it's possible I have a few out, and thus my 10.0v voltage doesn't pull down as low as your 8.26v.

I'm betting my voltage is from a weak controller OR a partially compromised wire causing a partial short eating up some of that voltage. I knew the motor was tired but didn't think it was that bad. Had ~15-20psi at idle hot and ~25-30 at 2k rpm so it was low but guess it decided to just randomly let go. I don't think its injectors as those are genuine new (not reman) Bosch put in early 2019 and only have around 10k on them since always supplied by a FASS with regular filter maintenance. It isn't a broken crank as the truck still charges. I'll check the balancer tonight and see if it is wobbly but it idles smooth. As soon as you increase RPM there is a loud knocking sound coming from the engine bay that distinctively sounds like bearing failure.


I have all the parts to rebuild it as long as nothing got hurt (crank) besides the top end gaskets and rings. I'm hoping to just put new rings/bearings/oil pump/oil cooler etc in and not have to bore it (hoping a ball hone does the job).