Mercedes: 1989-569 SL - wont start -, electric fuel pumps, fuel distribution system

Question
My '89 560 SL will not fire when cranking. Had issue with car running a few times - changed plugs. ran fine for two months. Then had issue with car not accelerating - either spark or fuel issue.  Distributor cap and rotor replaced. It will fire when you pore gas into throttle body. Checked the fuel line into the fuel distribution system - not much pressure. SO , I have changed the fuel filter. Still will not fire when cranking - sometimes fires but will not continue. Fuel distribution system got pressure - then lost it.

How do I proceed to correct starting problem. Where is the electric fuel pumps relay - somewhere in engine compartment ??? Have not found any fuse in passenger compartment associated with fuel relay or fuel pumps.

Appreciate understanding how to proceed - unemployed now and have limited funds.  

Bob

Answer
Bob,
If the vehicle will start with starting fluid and run momentarily, it indicates that you have a fuel delivery problem. The electric fuel pumps have a relay that is connected to several interrelated circuits. On my 420 SEL it is located along side another black box on the driver side  firewall. On your vehicle I am not sure the location. Try www.benzworld.org forums.
I purchase two of ebay and the vehicle ran, for a time. Then I traced a problem to the ignition switch. The terminals in the switch had gotten worn. I again purchased the electrical part off Ebay for 20.00.
Cannot tell you the difficulty i had installing the switch. I had to drop the steering column and remove the instrument display.Cold Start Valve is the usual suspect.

Here are some additional reason for stall.

Any of these can cause what you describe:

Overload Relay
Fuel Pump Relay
Alternator
Voltage Regulator
Battery "sulfated"
Ignition Coil "breaking down = old age"
KE Control Unit
Reference Sensor
E.H.A. Valve
Idle Control Unit
Idle Control Valve
Oxygen Sensor
Water Temperature Sensor "for computer".
Fuel Accumulator
Fuel Filter "plugged"
Fuel Fitting "LEAK"
Fuel Hose "LEAK"
Fuel Hose Clamp "LEAK"
Fuel Line "LEAK"
Fuel Pump
Fuel Tank Vent Valve "plugged"
Catalytic Converter "plugged"

Hope this helps.
Rob