M818 keeps cutting off..... knocking bad.

[Cam Morehead]

I think I am dealing with a fuel problem. The truck cut off going down the highway. I let is sit for an hour and it started back up. It has done this 3 times now. I found a kinked hose from the discharge side of the selector valve. I decided to take the fuel line loose from the discharge side and the passenger side fuel tank. I do not use the driver's side tank. I hooked the line up from the passenger side tank and plumbed it straight to the inlet side of the fuel filter. I did not bypass the selector valve for the return line. The truck ran rough, like it has been, for about 2 minutes and then cut off. This is not what it had been doing..... Now the truck will not start and if it starts it only runs for a second and cuts back off. Do you have to bypass the selector valve for the return line also? Can this thing suck air if I do not plug the open holes on the selector valve? Should I just bypass the selector valve for the return line also? Thanks, Cam

 

[Floridianson]

I too have bypassed the slector on one of mine. I did bypass the return line though. The only problem I see with that from what I understand you did would be someone playing with the slector and it restricts the return flow. So yes I think you should correct the bypass.

 

[73m819]

BYPASS the selector valve, it is known for bad O-rings and the lines from it to are bad for cracks that suck air, run a NEW hose, the truck will not start because your system is FULL of air. Why do you NOT use the left tank ???

 

[Cam Morehead]

I don't use the left tank because it is full of trash.... I cleaned the passenger tank and choose to use it since it is clean of trash. I can bypass the selector valve for the return line also but I guess I was asking if there is any way for the set up I have to suck air? The truck ran before but it was rough. Now it will not run. It starved our for fuel. If I prime is lots it will try to crank but will not stay running.

 

[73m819]

This is because you ARE still sucking air, also what is the fuel filter like, is the flat washer on top of the filter in the recess and flat, if not the top o-ring will not seal.

 

[Cam Morehead]

The big fuel filter under the driver fender is good. I replaced it last year. I drained a tiny little bit to check the quality of the fuel. It looks good. When I pump the primer on the dash, it drips a little diesel fuel. I guess I need to replace these o-rings and bypass the selector on the passenger return line. Now that I have air in my system, how to get the air out? Crack the valve on the intake 1/8" primer line? Thanks, Cam

 

[tstone]

I agree with the others, you are sucking air. If your hoses are still good put stainless steel hose clamps on each of the fittings, the OEM connections fail after 30 years and will allow air into the system even though the connection appears to be fine. The fuel selection valve is easy to rebuild, disassemble it, replace the o rings if necessary and lightly lube them with fuel before reassembly. I've done 2 of these and have completely eliminated and air issues, it's also great to have a working fuel selection valve if you rely on the 2nd tank. Good Luck.
Tom

 

[Stan]

If you changed the lines and didn't bleed the system you have air in the lines. The fuel tank can be pressurized thus forcing fuel through the lines. Start at the tank working toward the engine bleeding air and checking for leaks. If you'll do a search on this topic you will find more indepth info.

 

[Floridianson]

Yea I would say that you just picked up some air. If you ran a good tight line from the tank to the filter and your pickup tube is correct then the return even going through the slector valve would not put air in the system. Correct the return and eather crank the truck over and it will pull out the air or open the bleed screw on the prime pump and pump it till all air is out of the system. Sometimes when pumping you will get good flow and you think you done but you are just clearing the line from the outlet of the fuel filter to the pump. So if that is the case if you keep on pumping it will pump and start to spit out the air the it will get solid pump of fuel. When you a happy with the flow and no more aiir is comming out close the petcock on the manifold and go for start. This can be a lot of work. I just crank the motor over for fourty seconds wait two min. then crank again for 40 and if is all correct with the incomming line to the TP it starts.

 

[Cam Morehead]

I feel like a complete idiot...... I have been wrenching for 20 + years and just got annoyed last night and was working in the dark with a flashlight between my teeth. I worked on it for 5 hours and got aggravated at the end...... I went to bed mad and woke up mad. I drove to work this morning in the dark. I pulled in to the parking lot at work and it hit me like a ton of bricks...... I said "You idiot, you took the lines loose and all the fuel ran back to the tank..... You have to pressurize the tank, take a nut loose, and prime the entire fuel line from the tank to the filter...." I appreciate all the replies, but I still feel like an idiot.... It was a long day yesterday and the madder I got, the less I could think straight.... I will try to work on it Saturday..... working too many hours during the week. Cam

 

[Floridianson]

I feel like a complete idiot. You have to pressurize the tank

No just crank it over it will clear.