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 problem.
1. Possible malfunction of the fuel regeneration valve
2. Leaking fuel injection valve

Thanks for any help

 

....allowed fumes to escape from the engine.

If you are referring to what I think you are referring this SHOULD BE

...allowes fumes to escape TO the engine.

The engine consumes vapours from the tank system. Usually the mechanism is part of the fuel filter on current cars . Not sure about your vintage. If this system is defective you will likely get the symptoms you are describing.

On the other hand maybe you are describing the crankcase ventilation system. This permits the engine to consume its own fumes. This also can give symptoms similar to what you describe.

Stuart

 

You are right, I thought it was a fuel return line. The following is information I have recieved from another forum. Let me know if you have any additional thoughts after reading it. This weekend I plan on putting a fuel pressure gauge on the injection rail and see if I can get a better 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.





--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.

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It has been over a year since I posted my hard to start problem, and just by accident I solved the problem. It turns out the chip in the smart key was faulty and I only found out by chance, when I used a spare key and the car started with no problem.

 

So the car would crank OK but sometimes with no ignition or the immobiliser operating with the "defective" key?

My limited understanding believed that this was not possible since a single signal switches both the cranking and immobiliser circuits....

BUT YOUR EXPERIENCE SUGGESTS DIFFERENTLY.

Can anybody add more to this? Bazzle, Ohlord, Chassis 221 etc.

Stuart.