Fuel regeneration Valve / Fuel Injector ????
 

Fuel Regeneration Valve / Fuel Injector ?????

I have a 1998 ML320 that cranks for about ten + seconds before it starts. MB dealer said it had a leaking check valve in the fuel pump and replaced it along with the fuel filter. It did not solve the problem. I have learned that the fuel filter also incorporates the fuel pressure regulator. (It has four ports on it)
I found that if I turn on the ignition key for about 10 seconds before cranking the engine, it starts within a few seconds. When I turn on the key, I can hear a humming noise at the engine (which I assume is the fuel pump running) which does not stop even after running about 60 sec.
On the fuel return line, is what is called a fuel regeneration valve. (mounted on the fire wall) The
parts man said the MB tech at the dealership told him that it allowed fumes to escape from the engine. ????? He could not explain how it
worked. I am wondering, if it is a valve that closes when the engine is turned off, to maintain fuel pressure between the fuel pump and fuel injectors.
So I am down to two possible reasons for my problems.
1. Possible malfunction of the fuel regeneration valve
2. Leaking fuel injection valve

Thanks for any help

Nope, you got it all wrong!!!

First the 112 motor uses a returnless fuel system. In other words FUEL goes one WAY, no return.

Next the regeneration valve is otherwise know as a purge valve. It is used to purge fuel vapors that are trapped in the charcoal cannister. It has absolutely nothing to do with fuel system pressure or delivery. It can cause a rich mixture if stuck open when there is fuel in the cannister and a lean mixture if stuck open when there is no fuel in the cannister.

Another issue would be that I can't imagine the fuel pump running without the engine or starter running.

It seems that the system is loosing pressure when shut down, so with a new fuel pump and filter how is that occuring? Leaking fuel injector?

An injector leaking down will cause a problem on a hot motor, but not likely on a cold one. A cold motor needs no residual pressure. It will start fine as the fuel pump provides pressure on cranking.

If your issue is pressure, that motor is the simplest to measure pressure. There is a service port at the front of the rail. If you suspect a injector problem put a hose on the service port and crank the motor. Collect a pint or so of fuel and observe it. Due to the returnless nature of the fuel system it has the ability to trap/accumulate debris in the rail. A good purge every once in a while often does some good.

This weekend I plan on putting a fuel pressure gauge on the injection rail ,after flushing it as you suggested and see if I can get a better idea of what is going on. The fact that I can turn on the ignition key for about 10 sec before cranking, and it starts right up, makes me think that it is some how loosing pressure and or fuel in the supply line.
One thing I did not mention is that when the engine starts, there is a strong smell of gas fumes outside the vech. and this is a problem when the engine is hot or cold.

Thank You