Problems with my 800 series fuel system ! help !

I own 2 M-812 trucks, 250 Cummins, both low miles. One is running fine, the other is starving down on fuel. Will run aways and then starve down. I dropped the canister filter under the left front fender. Filter seemed clean and there was no sediment in the bottom of the canister. The canister was only about half full of fuel. OBSERVATIONS: the petcock at the bottom does not seem to do anything, it actually sucks when the keys are on and the engine not running. It is connected to the stem, rather than the bottom of the canister. I assume that the fuel pump is in the tank. When the good truck is running, you crack the nut on the line at the tank and nothing really happens. When the switches are on and the engine not running, you crack the nut and nothing still happens. Any ideas, on how to check out the fueling system? Tom

cummins? isn't the fuel pump on the engine?

there is not an electric pump on my XM818. there is also a filter in the ip. dont forget to add your location to your sig.

Sorry, just getting registered to this site. Located in eastern Idaho, I run a 1800 acres potato and malting barley farm and use one truck to haul produce and I kept the other origional for a recovery truck. www.snakeriver4x4.com It helps to read the book, apparently you have to crack the upper petcock to release the air for fuel to come out the lower petcock. Will change fuel filter tomorrow and reprime the system. Will let you know how I come out. Tom

Tom, there's also a procedure to prime the system with the drain type valve at the top of the flame heater manifold and using the hand priming/flame heater pump handle in the cab. That evacuates air from the system after you've either drained the fuel filter or changed it.

First off the ip on the cummins is the fuel pump. If you are getting air in the system it won't run. I had a problem with my m816 . It would start and stall .couldn't keep it running. Guys told me it was an air in the line problem . I had a small kink in the hard line from the filter to the IP. changed it. then I went to the tank switch, thats the lever on the floor next to the drivers seat. I took it all apart an lubed it with white grease. re assembled it an did not solve the problem. I next replaced the six rubber hoses that are about eight inches long with the barbed fittings on each end. these are the sourse of the problem . when replacing the hoses , go ahead andput a hoseclamp on each one and torque them down well. Problem solved . Truck is running fine for two years since.