I've had an ongoing problem with this car with hesitation with rapid and full throttle advance. Spark - OK. Cylinder pressure - OK. Exhaust backpressure - OK. So now I'm looking at fuel delivery and am at the fuel pump relay test with the following results.

step 1.0 - OK, pump runs with pins 7,8 bridged
1.1 - 5.45 volts, pins 9,11
1.2 - 6.54 volts, pins 10,11
1.3 - 3.78 volts, pins 11,8
1.4 - ok

The circuits are not open but it looks like they soon will be. Is there a common place to look or do I need to continuity check each wire now.

by the way, the fuel relay module has the MAS sticker on it, Correct????
Intruder

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The fuel pump relay/controller is the MAS unit yes. Also it is the A/C compressor controller.

Have you replaced the ignition coil yet. This may appear to be good, but when hot and or under pressure will fail.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

yes I replaced the ignition coil but that only improved startup performance.

I was wrong on step 1.0. Jumping pins 7,8 do not run the fuel pump and was verified with 0 bar system fuel pressure. I started the car and fuel pressure was at 4.9 bar with about a differential pressure of about .1 bar. I didn't do a flow test since jumping pins 7,8 is a fail. I also got a potential of 0 volts across 7,8 with the ignition ON. I assume this is abnormal if this is to run the fuel pump.

So, where is fuse "F1"

and should the car even start if I can't get the pump to run by jumping pins 7,8??

Why would the test voltages be only about half of normal??

Intruder

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[This message has been edited by intruder (edited 02-27-2000).]