MBE 906 Losing Prime

[Snoopjohnny5]

I have a 2003 Freightliner Thomas bus lolwith a Mercedes 210hp diesel.
Motor has been flawless. Started it one day to run it and move it. Ran for 30 mins. Turned it off. 2 days later I went to start it and nothing. If I bleed the injector lines it will start and run great. When I shut it off, I can immediately start it back up no problem. If I wait 10 or more mins, it won’t start unless I crack the injector lines and bleed it again. I have replaced the inline fuel filter in the frame rail, replaced fuel pump and replaced 2 check vale’s going into fuel filter housing. Still does the same thing. The other fuel filters have about 3000 miles on them. I don’t see any fuel line leaks. I took plate off above tank and it’s a brand new fuel tank.
Any ideas?

John

[joeblack5]

What part of the fuel pump did you replace? There are several check and bypass valves in the fuel pump assembly..
I had a similar problem and replaced the engine driven file pump with an electric pump. Problem went away.

Good luck,
Johan

[ewo1]

Originally Posted by Snoopjohnny5

I have a 2003 Freightliner Thomas bus lolwith a Mercedes 210hp diesel.
Motor has been flawless. Started it one day to run it and move it. Ran for 30 mins. Turned it off. 2 days later I went to start it and nothing. If I bleed the injector lines it will start and run great. When I shut it off, I can immediately start it back up no problem. If I wait 10 or more mins, it won’t start unless I crack the injector lines and bleed it again. I have replaced the inline fuel filter in the frame rail, replaced fuel pump and replaced 2 check vale’s going into fuel filter housing. Still does the same thing. The other fuel filters have about 3000 miles on them. I don’t see any fuel line leaks. I took plate off above tank and it’s a brand new fuel tank.
Any ideas?

John

I know nothing about MBE engines…. But I found this interesting post on another forum where the guy had the same problems you have.

It kinda points to what Jose lack is pointing at, check and bypass valves.

Let us know if it was helpful…

Good luck!

[magnakansas]

Ever try to suck up a drink through a straw that had a crack in it?

tiny tiny tiny crack will dump vacuum and never get the fluid up under suction conditions...

I have seen more than once where a rubber line is porous and sucked air through the walls of the hose..... the remedy was to change all the rubber in any areas that "sucked" fuel. pump in the tank and pushing fuel was a different ball game.

william

[Snoopjohnny5]

I replaced the Main fuel pump bolted to the front of the block.

[Snoopjohnny5]

I replaced the 2 check valves that screw into the filter housing on one side and has the line coming in from Fuel tank on one end and the return line that goes back to tank. I cant find any other check valves.

[joeblack5]

When mine had the same problem I took the fuel pump assembly off. If I remember correctly, probably should re-read my posts 3-4 yrs ago on this issue, the output of the gear pump goes into a fuel gallery in the engine blocks casting.

A new pump for the mbe was $180 or so, a rebuilt kit a lot cheaper...bearings..o- rings..etc.

With some studying it showed that there is a bypass valve integrated in the pump housing so that fuel can be pumped thru the system with a hand pump. See mbe manual and articles.

Anyhow ,my bypass valve was broken and was not on the rebuild kit. Without a partnumber I could not buy one and it looked to me that it was very hard to replace since it was stamped I to the casting... Very similar to the checkvalves stamped into the mechanical fuel.pump of the power stroke 7.3..

That is how I recognized that it was even a checkvalves.

Maybe you have some debrie stuck there or yours is a rebuild unit without a new bypass valve.

I do not know.. in that time I decided to replace the mechanical pump with an electric Mallory pump.. check out my earlier posts on this problem.

I can only say that last week I tried to start my mbe after 2 yrs sitting for our upcoming trip and it it is very comforting to hear the electric pump building up pressure and be rewarded with an immediate start within one crank.

Good luck johan

[sportyrick]

Of course you could wire and plumb in an electric fuel pump now just to prime to start. Of course that is going to present a visit from Murphy down the road but would get you going now. The way the valves in most in line fuel pumps work you can pull fuel through them when not turned on.

[joeblack5]

Took some while to find my old post regarding our mbe 906 fuel pump problem.

Thread: not a skoolie
Post376

This is all a long time ago.
Johan

[Snoopjohnny5]

Can someone tell me the purpose of this and what would happen if it didn’t work?