Cummins cold start question.

[TheBuggyman]

Used to be that when I turned on the fuel heater the indicator light would go on full bright and the other morning it came on like usual and then dimmed down to almost nothing! What gives? I am getting about 2.7 volts to the heating element when the switch is on and about 10.7 volts to the switch. I do not have a wiring diagram for this truck so I'm reduced to guessing and tracing wires. The truck still starts good though.....
Any suggestions or diagrams out there?

 

[WillWagner]

What engine is it?

 

[TheBuggyman]

It is the Cummins 855, or NHC-250 I believe.....

 

[WillWagner]

OK, i'm stumped! I have no experience with them, been in Southern Ca, so we never had to work with them. Tried the oldest manual I have, 1981, nothing in it and also tried on line at Cummins. No info, Sorry

 

[TheBuggyman]

Thanks for trying Will!

 

[Jones]

For starters, what truck are you working on? 12v or 24v system?
A place to start is by looking for dirty contacts at the switch and at the heater. Or a wire breaking down inside it's insulation.

 

[TheBuggyman]

For starters, what truck are you working on? 12v or 24v system?
A place to start is by looking for dirty contacts at the switch and at the heater. Or a wire breaking down inside it's insulation.

It is a 24 volt system in a M813-A1 (5-ton). Cummins NHC-250 855 cubic inch engine. Already checked the basics (the switch and relay contact resistance <1ohm. I do not know if there are resistors or any other type of controllers used in this model. I really need a diagram or someone that this has happened to tell me what to look for. There is a control box on the firewall that I have no idea what it does!

I do building energy management controls so I am well versed in electrical theory and operation but I was trying to avoid cutting apart my harness to trace wires.

 

[Jones]

No need to chop into anything yet. Let me see if I can lay my hands on a wiring diagram for you.

 

[1958 M274]

Pull your glow plug and check to be sure it did not burn out… That is what happened in my Dad’s M813A1. The 809 series trucks use a weird system with 6, 12, and 24 volts!

 

[TheBuggyman]

Pull your glow plug and check to be sure it did not burn out… That is what happened in my Dad’s M813A1. The 809 series trucks use a weird system with 6, 12, and 24 volts!

Glow plug is good (not open), I don't know if the resistance is correct though. It does get hot, but not glowing red.

6,12 and 24v!?!?! No wonder I'm having a time!

 

[TheBuggyman]

No need to chop into anything yet. Let me see if I can lay my hands on a wiring diagram for you.

That would be an answered prayer!

I hate chopping!

 

[GIJoeCzar]

Hello,

I've been running these small cam 855s for some time and I don't even dick around with that "spark plug". When you're away from 110v power give it a shot of candy (ether); the Cummins like the candy. Don't over do it or you'll over rev the motor, and that's a bad thing. The Cummins are cold-blooded, so your best off warming them up.

The ABSOLUTE best thing you can do is invest the $45 buck in a block heater (frost plug heater). My trucks sit in Northern Wisconsin and in the middle of the winter I can plug it in for four to six hours and she'll fire off without even giving her candy. Block heater is the way to go -- period.

I've uploaded a photo of where the block heater gets installed. The best place to put it is the hardest to get at as the exhaust manifold is in the way (can be done, just hard when motor is in the truck). Second best is just fine, but you've got to ensure that you turn the element 180 degrees from the way it comes in the box, or it won't heat the block as well. Go to () for a photo (http://www.czarnik.net/joe/My_Stuff... Cummins Small Cam Block Heater Locations.JPG).

By the way, I'm in Carlisle now and often go to Fredericksburg to visit my son (I was stationed at the puzzle palace 98-02). How many M809s do you own. You can see mine at (http://www.czarnik.net/joe/My_Stuff/5_Ton_Trucks/Joe's%20Motorpool/DSC01611.JPG).

Good luck!

CZAR

 

[BKubu]

Joe,
Welcome aboard!

 

[Gamagoat1]

Hey Buggyman,
I have the diagram for you that shows the Cummins cold start system. It's from TM9-2320-260-20. My M816 had a similar problem. The previous owner changed from 4 batteries to 2 but failed to wire the cold start correctly. It's a 12 volt feed to the cold start system.
Let me know.
Mike

 

[GIJoeCzar]

Hey Bruce, thanks. You going to be at home tomorrow? I'm coming through on my way to Fredericksburg tomorrow (Sat, 9 Dec) and would love to swing by if the timing is good for you. Also, who was the guy with the M945 and what was all the fuss? I'd be happy to sell my remaining four 5-tons (M813, M923, and two M925s w/ABS) as a package. (http://www.czarnik.net/joe/My_Stuff...9 Series 5 Ton trucks That I Want TO Sell.doc). Joe