Brief Wait to Start Light Flash Only at Night?

[diesel_dave]

Hello everyone, I've spent a considerable amount of time scouring this forum for this specific version of a wait to start light issue and I've turned up nothing. I work at night so I get home around midnight (temps low 30s) and all week when I try to start my 2006 M1152, the wait to start light just lights up for about a second and the glow plugs don't appear to be doing anything. I curse and go to bed since it's dark and cold and there's not much I can think to do to troubleshoot. I wake up around 1100 (temps in the low 40s) and I go out and everything works perfectly fine. Done this every day this week and it's making me crazy because I can't duplicate it during the day. I have tested a few glow plugs and about 50% have been burned out so I have a set on order and should be here next week. I have a yellow label KDS box and TCU. I've checked and cleaned every ground and connector I can find and haven't found a single issue yet. This is obviously temperature related (must be, right?) but it's not even a wide temperature swing between 30 when it doesn't work and 40 when it does. Y'all have any idea? I'm completely perplexed. Hoping the glow plugs somehow fix it but I'd think it would never work if the plugs were the problem...

Thanks in advance and sorry for another "wAit tO sTART lIgHt dOeSnT wOrK" post!

 

[Milcommoguy]

Hello everyone, I've spent a considerable amount of time scouring this forum for this specific version of a wait to start light issue and I've turned up nothing. I work at night so I get home around midnight (temps low 30s) and all week when I try to start my 2006 M1152, the wait to start light just lights up for about a second and the glow plugs don't appear to be doing anything. I curse and go to bed since it's dark and cold and there's not much I can think to do to troubleshoot. I wake up around 1100 (temps in the low 40s) and I go out and everything works perfectly fine. Done this every day this week and it's making me crazy because I can't duplicate it during the day. I have tested a few glow plugs and about 50% have been burned out so I have a set on order and should be here next week. I have a yellow label KDS box and TCU. I've checked and cleaned every ground and connector I can find and haven't found a single issue yet. This is obviously temperature related (must be, right?) but it's not even a wide temperature swing between 30 when it doesn't work and 40 when it does. Y'all have any idea? I'm completely perplexed. Hoping the glow plugs somehow fix it but I'd think it would never work if the plugs were the problem...

Thanks in advance and sorry for another "wAit tO sTART lIgHt dOeSnT wOrK" post!

BOX is BAD.... Time for CAMOTEKSYSTEMS.COM

Stop cursing and smile, CAMO

 

[diesel_dave]

BOX is BAD.... Time for CAMOTEKSYSTEMS.COM

Stop cursing and smile, CAMO

I'm kind of wondering if that is the case. Cold solder joint, corrosion inside the box, something like that that is responding to changes in temperature. Sun shines and heats up the KDS box and it works. Night time and it cools off and stops working. Something like that.

 

[MarkM]

I had many issues with the glow plug system. My biggest problem was a box. The main solenoid got stuck and fried the plugs. PITA. Anyway got everything sorted out and I made a very quick video on how I tested the system. Hooked up a volt meter to the pass rear glow plug (alligator clips) and observed the operation.

Mark

 

[Mogman]

Could it be a bad temp sending unit, failing when the temp is lower?
Oh yes, put a dash light on your truck connected to one of the glow plugs and you will always know what the glow plugs are doing...

 

[diesel_dave]

Could it be a bad temp sending unit, failing when the temp is lower?
Oh yes, put a dash light on your truck connected to one of the glow plugs and you will always know what the glow plugs are doing...

That thought crossed my mind. I guess I need to find a schematic that shows how that circuit works so I can get some readings during the day and again at night to see if there is something going on there. Good idea about the glow plug light. I'm going to hook up my oscilloscope and see if I can get a better idea of what exactly the KDS box is doing with the glow plugs.

 

[juanprado]

Which box do you have?

 

[diesel_dave]

Which box do you have?

I have the KDS yellow label. I just "discovered" some interesting things about my issue and how the yellow label behaves. I am putting it together in a post right now.

 

[diesel_dave]

Okay all, I had some time to dig into this today and I think I got to the bottom of it (hopefully).

I kind of focused in on the temp sensor when I noticed that I could duplicate the brief flash behavior after messing with the temp sensor connector. I could jiggle it one way and it would work and then jiggle it again and it wouldn't work. After doing that a few times I noticed that the whole entire circuit board actually was just kind of resting in the housing and could be pulled right out. That's when I saw the thermistor was covered in wet dirt that had accumulated in the temp sensor housing. The circuit traces were badly corroded and the thermistor actually just broke off at the lightest touch. Thankfully, I had a 10k thermistor laying around so I reflowed the solder joints and soldered on the new 10k thermistor. I tried it out and to my great surprise, it actually worked! I need to try it a few dozen more times to be sure its not a fluke but it is looking promising so far.

This lead me to my next "discovery" that I am sure other folks probably already knew: it doesn't seem like you actually need the temp sensor to even be connected! I had my o-scope hooked up on one of the tests I ran with the temp sensor unplugged and noticed that the KDS box appears to operate in a sort of battle short mode and it ends up enabling the glow plugs for about 5 seconds with about 2 minutes of quick afterglow pulses then it disables the glow plugs and everything works perfectly fine.

I can only speak to the yellow label KDS box that I have, but it seems you don't need the temp sensor at all if you don't mind the glow plugs cycling a little bit when the engine block is already warmed up. On a cold engine, it seems to act no different than it does with the temp sensor connected besides the fact that the wait to start light flashes instead of staying lit up solid.

So, I'm going to see how my shoddy fix works and if it starts having problems again, I'll probably just seal off the temp sensor connector so it doesn't get water in it, and run it like that unless someone says that's a bad idea.

Here is the video of how it behaves with the temp sensor disconnected:

 

[MarkM]

If you run a full cycle on the plugs when the engine is hot you will overheat the plugs.

Mark

 

[diesel_dave]

If you run a full cycle on the plugs when the engine is hot you will overheat the plugs.

Mark

You think the 5 second plug cycle on a warm engine will ruin them? Dang