Starting problems - possible fuel leak? - PeachParts Mercedes-Benz Forum

carlton · #1 01-30-2004, 03:17 PM

Hello all,

My first post to this forum - all the way from England! You all seem very knowledgable so I hope you can help me out on this one...

I have a 1995 E300 diesel (not the Turbodiesel). It is the W124 model with a 606 engine. For the last few weeks I have been experiencing intermittant problems with starting. It's not especially cold over here and in fact the weather doesn't seem to make any difference at all. The preglow light comes on as normal (looks bright enough) and then goes out. Normally it would start immediately when I crank the engine but occasionally it will just about fire up but then suddenly dies within a second or so, almost like a fuel starvation problem. If I then try to restart after it has stalled it will just crank over and over until eventually the battery is flat.

I read in the manual that it has an automatic bleeding system (not a hand pump system like the older models) but even if I follow the instructions it just doesn't start. I can crank it for over a minute on the starter motor but no sign of life. I really worry about burning out the starter by trying to crank it for that length of time.

The thing that puzzles me is that I have noticed how the problem only occurs when I park on a slope - even a very shallow slope - with the front end pointing up the slope. If I park with the nose of the car pointing DOWN a slope I don't get the problem. This could be a coincidence but it has happened so many times I am beginning to think there is some connection.

The battery seems absolutely fine. I had a AA technician over to help start it and he checked the charge. All seemed OK. He only managed to get the car started by (and you will probably think I'm nuts for using the stuff) spraying a little 'Easy Start' starter fluid into the air manifold while I cranked it over. He disconnected the air intake hose from the manifold to do this. He was able to get it to start on the fluid which in turn seemed to 'pull' diesel fuel through.

There seems no real logic to this because sometimes it does it when the engine is warm, sometimes on a cold start. It definitely seems worse if I leave the car for a few days without firing her up.

Curious to find out about the problem, I was looking under the bonnet (hood!) today while the engine was running and noticed a smell of diesel fuel. I looked around for a leak then happened to notice a small amount of diesel around the emergency engine stop screw (it is a little black plastic knob with "stop" written on it). The engine was at normal running temperature. I noticed a slight 'bubbling' of the fuel (presumably a leak of either air or fuel?) from around the shank onto which the black knob screws. I am not sure if this could be the cause of my problem but is it possible that a small leak from this component (whatever it is) could be the cause of all my problems?

Could it be that there is a fuel/air leak from that area which, when parked on a slope, is causing diesel fuel to 'siphon' back through to the tank therefore starving the engine of fuel when I try to fire her up? It seems sort of logical to me but I am a novice so I would really appreciate your input and knowledge on this if anyone can help.

Thanks for taking the time to read my little post!

Cheers
Carlton

whunter · #2 01-30-2004, 04:20 PM

Hello carlton
Check your O rings on the tube going from tank to filter housing and from filter housing to injection pump.
If any of them are old, weak or bad; you will be sucking air instead of fuel.
Your description is text book for bad O rings or a micro crack in the fuel pick up line.
Have a great day.

JimSmith · #3 01-30-2004, 05:13 PM

Cheers Carlton and welcome to the site.

Any place where fuel can leak out is place where air can leak in when you shut down. This will make it necessary to purge the system before it will start, which sounds a bit like your problem. Repeated use of the starter for periods of a minute or more will wear the starter out.

A starter is designed for "intermittent duty" so it draws current to accelerate the engine to its starting speed quickly, then maintains that speed until the engine starts. This should typically involve a few seconds, and the starter motor never gets a chance to get really hot. Using this means to rate electric motors that see intermittent duty only saves cost and weight. However, running these machines at their itermittent duty rating for longer periods of time, repeatedly, ends up seriously overloading them.

Running for a minute at a time, time after time with little cooling off time between operating periods will bring the starter motor to a temperature approaching the temperature it would reach at constant duty at that load. Motors are rated by the temperature the winding reaches under load that is considered safe for the design life. In the starter motor application the load is not acceptable for the motor in constant duty and the safe temperature is rapidly exceeded. When that hapens the insulation is degraded and that causes losses that limit the available torque (which means it limits the starting speed of the motor as it tries to crank the car engine over). This, in turn, limits the likelihood of a successful starting attempt, leading to more use of the starter and so on until the starter is no longer useful.

So, you may have an air leak into the system when it is shut down, that is also causing you to wear out your starter motor. In any case, I would fix the apparent air/fuel leak first and then see how the machine performs. If all else checks out (glow plugs, clean fuel filters, clean air filter, correct viscosity oil, etc.) I would suspect the starter motor. Good luck and I hope this helps. Jim