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srter16 · 05-03-2025, 01:08 PM

Went from sea level to 2800 ft above. Temp swing from low of 56 to 48 degrees. After sitting couple nights went to start and ran out of fuel. Fuel system had lost prime after sitting. Anyone have this issue before? Can I install a FAAS system inline with the mechanical lift pump? Any known elec feed back issues if one is installed?

Skip426 · 05-03-2025, 05:00 PM

Did you manage to start the coach ?
Is there still a manual prime pump on your coach ?

Many members have installed the FASS system on Cummins ISC with the CAPS injector pump ( that also has a mechanical lift pump section like the HEUI ) and have no issues.

A lack of fuel pressure on our engines can also be a sign of a failing manual fuel pressure regulator ; on the return line to the fuel tank at the back of the cylinder head.
Without the 65psi in the cylinder head fuel chamber that the regulator maintains the injectors don't put fuel properly into the combustion chamber.

srter16 · 05-04-2025, 02:32 PM

Did get coach started, after getting fuel system primed.

Cat · 05-04-2025, 10:58 PM

Quote:

Originally Posted by srter16

Went from sea level to 2800 ft above. Temp swing from low of 56 to 48 degrees. After sitting couple nights went to start and ran out of fuel. Fuel system had lost prime after sitting. Anyone have this issue before? Can I install a FAAS system inline with the mechanical lift pump? Any known elec feed back issues if one is installed?

How do you know you lost prime? Altitude doesn't usually cause a loss of prime. Cooler air make it more important that the in let air heater is working. 3126 C7 are cold blooded engines.

srter16 · 05-06-2025, 10:30 PM

Cooler temps can cause fuel to syphon back to tank if breather is plugged. Removed return line off back of head. No fuel present during cranking, bled air and started with no issue.

Cat · 05-06-2025, 11:30 PM

Quote:

Originally Posted by srter16

Cooler temps can cause fuel to syphon back to tank if breather is plugged. Removed return line off back of head. No fuel present during cranking, bled air and started with no issue.

The return to tank check/relief valve has been know to bypass and cause your problem

Skip426 · 05-07-2025, 09:28 AM

I'll agree with Cat , something in your fuel system isn't right, to allow fuel flow from the engine back to the tank while sitting; or the forums would be full of similar complaints .

I have driven several times with the altitude and temperature changes you describe and had no issues.

Does your fuel system pressurize the tank while driving ?
Fuel caps have a warning about opening slowly ?

ftodaro · 05-18-2025, 05:48 PM

I have two friends that have the same rig that i do, a 2001 3126B Itasca Horizon. Our rigs have a hand pump on the fuel filter to prime the system when you change out the fuel filter. Both of my buddies have had a failure in the primer pump, such that they lost the prime on the system and they could not start the engine. The pump is a 70.00 part and two bolts to replace it. I carry a spare, but if you ave this primer pump, i would check it also.

tinpeddler · 05-19-2025, 09:35 PM

I had a similar problem I would loose prime on lite throttle and would stall occasionally. I would use the manual pump and it would start and run fine. Then on lite throttle it would stall again. The shop I use couldn't duplicate the problem until I had it in for oil service and when they pulled it out to park it it died. Ther found that one of the fittings on the lift pump was cracked and when it had the perfect amount of pressures it would allow air to be sucked into the system. Once that was replaced I've had no problem. Maybe this might help, air is a big problem in our fuel systems.