M927 water tender idle issues

[LevitaVFD]

Hello everyone thank you for adding the levita volunteer fire department to this forum. We have a m927 im unsure of the year but we use it as a Tender (water truck) and we love it cause it can go places normal tenders can't go. We never had a problem with the truck until last week when it just all of a sudden died and would not start. If finally did a couple hours later and we brought it back to station where our mechanic looked at it. He did a fuel filter change on it. He's worked on Cummins but nothing this old or big and he does not know what is wrong with it. He believes the low end of the pump isn't picking up fuel so he added an aftermarket fuel pump to help but it didn't help and has a high to lower idle the truck has lost alot of its power and we need it up to 100% because it's a vital part of rural firefighting. Please help any advice
-Non turbo Cummins
-m927 20 ft 6x6

 

[Elijah95]

Pull the fuel pickup tube from the tank, they like to crack and sometimes even fall off, sucking air and shutting you down


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[98G]

I suspect someone tampered with the manual primer pump and failed to return it all the way in. This is worth checking....