Wednesday, December 15, 2010

Bleeding Diesel Fuel System - Mercedes MBE 900 Engine

We learned the hard way & experienced troubles trying to prime the Mercedes MBE 900 Diesel Engine. It was a chore trying to get it started again after it ran out of fuel.
Pressurizing the fuel tank and bleeding the system at the fuel lines was tedious and a crude method to say the least.
Most of these engines come from the factory with a quick coupler located at the fuel filter housing. The 2005 and earlier models have to be installed with the new coupler, a kit can be obtained from the Mercedes dealer.

We acquired the female quick coupler from the local dealer and added a  hose along with a stainless steel pressure tank similar to a lawn fertilizer set up.  There isn't a lot of  pressure required to bleed the fuel system, all it takes is 5 p.s.i or better. There is a bleeding apparatus available that we are looking at picking up. I will re-post when it arrives and give it a test drive.

This tank has to be topped up with diesel and pumped continuously while a second person cranks over the engine. It works great and saves a lot of wear and tear on the starter!

Note: there is a Technical Service Bulletin on the Thomas C2 School Bus models having a defective fuel gauge senderThe sender must be removed and tested with an ohm meter. We had some incidents on one of our C2 units running out of fuel prematurely.

Once you get this pressure tool all set up it will make removing the air from a Mercedes MBE 900 Engine fuel system much easier.


Anonymous said...

didnt know how to ask but im a school bus mechanic in south carolina you might know that we are owned by the state. well new governor is talking about privatizing the bus maintenance. I just wanted to know if you might know how they do this and if we get to keep our jobs or what? thanks

J. E. Whelan said...

That's a tough decision to make especially when operating school buses. In Canada the private company keeps the crew on but may drop the wages. The maintenance suffers as well. I hope it never happens. Good Luck!

The Rudstroms said...

I have a similar "Hudson" sprayer that I use in my shop to provided pressurized fuel to engines. I recently used it to test a fuel injected snowmobile engine that had a faulty fuel pump.
Here is a link to my blog showing it in use.

Please use great care whenever working with pressurezed fuel.


esau said...

can i used an eletcal fuel pump to supply and pressurize the system from the quick couplor at the fuel filter need that bleeding apparatus

J. E. Whelan said...

Hi There Esau,
Yes, anything that supplies some pressure into the fuel system will work. You have to be careful how much press. you use. Our shop bought a weed sprayer originally and just bought the couplers and hooked up a regular rubber hose. So if you use a pump make sure it only supplies approx. 5 psi (all you need is a positive press)

Anonymous said...

Once you pressurize the primer tank, do you leave it hooked up and crank the engine or should I close the valve and take it off. Is the a bleeder to open? Do you open the fuel tank?

J. E. Whelan said...

Leave the primer hooked up while cranking. You don't have to touch the fuel tank cap.

Anonymous said...

little cornfused. does this procedure push air out and in to the cylinders? why would you need two people? using two people keeps the pressure (5psi), up while cranking? what about the air from the housing back to the tank? this is also pulled due to the engine running off of the fuel from the 5 psi tank? And the engine runs rough as the air pockets hit the injectors?
William jones

John Whelan said...

There is fuel in the primer and it simply adds a low pressure feed to the filters and lines.