5 Ton Issue

[pwrwagonfire]

Gentlemen,

Our 5-ton at work has this issue...
Apparently it runs and drives perfectly, but when you leave the truck to idle, it stalls out.


I know that this is cryptic....but any ideas on where I should begin looking this week? I searched the forum, but couldn't find anybody with the same issue


Thanks in advance!

 

[porkysplace]

This must be a question for Carnac as there a lot of different kinds of 5 tons.
Cracked rubber fuel lines ?

 

[gimpyrobb]

New truck? Old truck? Just developed this issue? Etc.

 

[Artisan]

What is the RPM at idle prior to stall?

 

[pwrwagonfire]

I will get the answers to these questions today for you guys! I'm unsure of the model, however I know it is a 1977. I will get that information.
I am new to this work location, and from what I am told it just developed this issue all of a sudden

 

[swbradley1]

5-ton, 1977 my guess is an 809 series with a NHC-250 Cummins. Next guess.

 

[Vintage iron]

I live in Mass. and I have a company that maintains 5 tons and 2 1/2 ton trucks. Give me a call and i can help you over the phone. Matt 617-650-2108

 

[Floridianson]

I would add almost any 5 ton replacing all the rubber fuel lines will eather fix or help stop any future problems. If nothing else think of it as a pre-emptive strike.

 

[BKubu]

Hard to say, but it could be as simple as a fuel filter.

 

[jcappeljr]

Sucking air ???

 

[tobyS]

Sucking air ???

That gets my vote...cracked line or fitting loose.

 

[pwrwagonfire]

Truck is an M813

I think you guys are on to something with the air leak...tomorrow I will check all the fuel line fittings

 

[pwrwagonfire]

I would add almost any 5 ton replacing all the rubber fuel lines will eather fix or help stop any future problems. If nothing else think of it as a pre-emptive strike.

Good thought! Will check with the boss and see if this is do-able $$$ wise...I know that the fuel filters were replaced to try and solve the issue, but it didn't help

 

[pwrwagonfire]

I live in Mass. and I have a company that maintains 5 tons and 2 1/2 ton trucks. Give me a call and i can help you over the phone. Matt 617-650-2108

Thanks! I will give you a call when we start digging deeper into the problem!

 

[Floridianson]

If all you hose fittings are barbed then it's just the coast of some rubber hose. The only outher that is not barbed would be the one going from the the filter base to the PT.

 

[pwrwagonfire]

If all you hose fittings are barbed then it's just the coast of some rubber hose. The only outher that is not barbed would be the one going from the the filter base to the PT.

Definitely something SIMPLE and fuel related then, excellent.

Why would idle make it die, is it because the fuel is interrupted when the vacuum from the motor goes down? I had a similar issue on my M-37, except that had an accelerator pump issue...

 

[tobyS]

It is probably a very small leak that is less significant at higher rpm, since it is pumping more fuel. While letting the pump get a small amount of air with the fuel, it is not enough to break the vacuum.

At idle, with less fuel flow, a small amount of air makes a big difference and once the vacuum is broken, then it's "sucking air".

I would be looking for a sign of wetness, since it can leak out when not running through the same crack that air is going in when it's running.

I think I have heard of something being sprayed on while running, maybe ether, that gives an rpm boost when you spray it on the opening...but I'm not sure.

 

[Floridianson]

I think I have heard of something being sprayed on while running, maybe ether, that gives an rpm boost when you spray it on the opening...but I'm not sure.
Yea that is done when looking for something like a manifold gasket leak on cars. On a carbed or throttel body any air leak after them could cause a lean mixture. On our direct injection a bad manifold gasket is just letting in dirty air but still could be checked with propane.

 

[FormerNewMVGuy]

Check the pickup tube in the fuel tank for pinholes.

 

[paradeduty]

Does the 5-ton with the Cummins use an electric, in-the-tank fuel pump like the multi-fuels? Someone on here had mentioned that the Cummins had enough vacuum to keep running when the fuel pump quit, so I was wondering if the vacuum might be too low 'at idle' to keep running if the pump quit, but high enough otherwise.