M931 fuel problems

[Carlo]

My 931 is giving signs of fuel stravation. Filter is good, tanks and clean, fuel lines are free. Shut off valve is checked and working. Please let it not be the pump! HELP from Italia.

 

[M35A2-AZ]

Sounds like it is sucking air from some place.
You need to check all the fuel lines for leaks, Fuel filter housing and the fuel tank switch valve.
Good luck!

 

[markmontana]

Which motor do you have? The 8.3 fuel pump can be a problem. Lucky they are easy to find and less than $100. (US)

And very easy to replace.

 

[Carlo]

Fuel Starvation

Thanks for the replies..

The motor is a 250 Cummins. Tanks and clean, no cracked lines, Fuel tank vaule is free and working (note old filter and all lines and tank and shiney clean, no rust, nothing).

 

[M35A2-AZ]

It can be just a little pin size hole.

 

[markmontana]

Here's a thread with 250 fuel problems. Air leak.

http://www.steelsoldiers.com/5-ton-up/91210-m923-hard-start-any-slight-incline.html

 

[Carlo]

I made a air valve on the fuel tank and pumped it up and checked for leaks but found nothing. PLus when its first running as in cold, either is still needed to start it but it runs better.,

 

[Csm Davis]

East way to check this on 939 series trucks is still or knock out one of the spots on the fuel cap, some tap it for a plug for after testing, undo your return line from top of the tank and put a plug in the tank fitting and GENTLY pressurize, no more than five psi! the tank and fuel will flow through the system. Catch the fuel from the return line in a can for reuse and look for leaks. If this doesn't show a leak then reattach the return line and try again With the system closed up but be east on the pressure 1 or 2psi is normally all it takes to show the leak, again do not over pressure the system it can damage it and you!

 

[Carlo]

Hi Jeff,
I did this same thing on sunday and heard no leaking air. Im going to check the gasket on the fuel fiter but Im sure I installed it right and besides it had the same problem before I changed the fuel filter.
I did remove the pump to the injection pump yesterday and spinning it by had you can feel it sucking againist my thunb. Im going to hook up a drill to get a better check. NOTE a trip to a Cummins dealer or a pump shop would be a quick fix but here in Italy the min cost would be €400 !! I must try to find the problem and fix it my self.

 

[goldneagle]

Hi Jeff,
I did this same thing on sunday and heard no leaking air. Im going to check the gasket on the fuel fiter but Im sure I installed it right and besides it had the same problem before I changed the fuel filter.
I did remove the pump to the injection pump yesterday and spinning it by had you can feel it sucking againist my thunb. Im going to hook up a drill to get a better check. NOTE a trip to a Cummins dealer or a pump shop would be a quick fix but here in Italy the min cost would be €400 !! I must try to find the problem and fix it my self.

I had a cracked brass elbow under the tank selector switch. That would let air into the system. Check there too. There are rubber hoses there that could be cracked. Did you try feeding fuel from the other tank?

 

[Stein12501]

Isn"t there a small filter in the top of the fuel pump housing? Might won't to check it. Don't have a number on the filter.

 

[Carlo]

I tried both tanks with the same results. Im going to check one more time before I take the pump to a expert for the cost here in Italy is out of this world! Do you know of a "in pump filter or screen"?

 

[goldneagle]

isn"t there a small filter in the top of the fuel pump housing? Might won't to check it. Don't have a number on the filter.

fp-146483

 

[Carlo]

Hey Stein...
I have the cut off valve on top of my pump. There is no filter there.

 

[Carlo]

I have the cummins 250 motor. On top of the pump is a fuel cut off both electric and manual. I have checked to see if this is working and it is.

 

[Stein12501]

Sorry Carlo I have not changed mine but I think there is a small filter on the top right next to the cutoff switch under a large cap. I saw it in the TM's and they had a write up showing it and looking for a number to replace it. I will see if I can find the thread.

 

[Carlo]

WOW you are right!!! I saw this BIG screw but I had the truck at my home and I dont have my complete set of tools there. Im at my shop now and its getting close to time to head home so I will bring a big screw driver and try this. I HOPE there is a filter and its frigging pluged!!!
This would make my day, week, month and year if I dont have to spend money on this pump. My sweet wife is ready to send me sleeping in the 931 if I ask for more family money to fix this pump.

THANKS from the heart!!!

 

[Stein12501]

I'll see if I can attach this. Sorry not real good at this stuff.


http://www.steelsoldiers.com/attach...-fuel-pump-filter-nhc250-fuel-pump-filter.jpg

 

[Carlo]

You are right 100% I see the filter and its under the mistery screw as my son called it yesterday. I cant wait to get home and find out.
Dear Sir I will keep you posted and THANKS!!

 

[Stein12501]

I hope that is it. If it is I will have to get busy and change mine. Best of luck Carlo.