Hi all, i have a Mercedes 1989 300SE , was working fine, then sudently when i crank it, the motor starts for 1 second , then stop.

I jumped the number 7 and 8 pins in the fuel pump relay socket, i can hear fuel is flowing in the pipes.
I changed the spark plugs.
I changed the battery.

Should i hear the fuel pump start when i put the ignition on, just before cranking? Cause i hear nothing.

Any idea what the problem could be? Any help would be appreciate.

Patrick

 

You should hear the fule pumps just before cranking. silence usually ends up with a no start.

 

Ok, i hear the pump for 1 sec just when i put the key to ON ( the notch before cranking) then the pump stop, so i shorted the number 7 and 8 pins in the fuel pump relay, then i put back the relay , i could hear the fuel flowing, so i pushed the airflow plate in the carb and it was kinda stiff with a fuel hissssing sound coming from the throtle body. i tried to start it, with the same result, you think i should try it with starting fluid, just to see if the problem is not on the lean fuel/pressure side?

Patrick

 

never tried the starter fluid method before personally but have heard it being done before on carb. vehicles.

If you hear the fuel pumps come on then stop that means they are primed. Normal.

Yet still no start?

Now it could be fuel pressure problem. Is there fuel flow to the cylinders with a good spray pattern or is it too little?

How about the spark plugs which may have nothing to do but sometimes it's easier to cover easy bases before throwing money/parts in the dark. What are the condition fo the plugs?

 

just curious your 1989 had a carburetor??????? that is absolutely new to me, those models and series comes with a fuel distributor and injection system and no such thing as carbs,

Yes you should hear a moment of hissing before cranking to start the engine and it should stop as soon as it has filled up the line, there is an automatic pressure switch that cuts the electricity signaling the fuel pump. and if the hissing sound persist without stopping before cranking the engine, then visually check if there is any leak from your fuel pump (located on the rear lower right side under chassis, close to the right rear wheel, it usually has a black plastic cover, check if there are gasoline leaks. If yes replace immediately. Normally on base on the age of the vehicle, the fuel distributor are most likely to be the culprit, that is if everything else is check out and still can't find the fault. the diaphragms usually breaks after a long period of service, either buy a rebuilding kit or replace with a brand new or re manufactured one.

 

Good news, i found a cracked vacuum hose under the fuel injection system/intake manifold. I just put some tape around it, now it works fine, i will order a new hose. Thanks to all of you guys for trying hard to help me!

PatrickNoel