I have a problem trying to start my 1994 E320 sedan. It seems that the fuel pump is not turning, either due to relay or maybe the fuel pump itself. I am confused though, becuz yesterday it was fine. driving around, then i stopped and turned off and about 5 min later it wouldnt turn back on, so had to have it towed to my house. THen earlier today, i went to try and diagnose the problem and disconnected the battery and reconnected and messed with the pressure regualtor a bit and bam it started, drove it around a bit, pulled it up to my driveway, turned off, tried to turn it back on and it didnt start, disconnected battery again, still nothing. Im thinking its some sort of loose connection, or maybe the relay. Speaking of which, where is the fuel pump relay, and how can i test it. any other information regarding my problems is appreicated. Thanks in advance.

My vin number is WDBEA32E4RC023725
1994 E320 Sedan

Thanks

j-mang

 

Mercedes had a problem with cold solder joints in the Over voltage protection relays in '94 and '95. It's the relay behind the battery with the clear flip cover over the fuse. I think there was an old service bulletin with this topic. If the date code is '94 or older, replace it and this will probably fix your car.

 

So in fact it is not the fuel pump relay or the fuel pump?. Is there a way i could test out this relay at all? Thanks again


j-mang

 

I've seen these relays drive people crazy trying to catch them acting up. The next time your car won't start have someone crank the engine and carefully flick the top of the relay with your finger. If it fires, you need a relay. The fuel pump relay is also in the same area, it's a green relay with a fuse in it. I've seen more over voltage relays go bad then fuel pump relays, but it's always possible.

 

I checked voltage readings across the place where u put the relays (not sure of techincal term) but the voltages were correct, i then since i got stumped began to unhook various sensors, and wipe any corrosion from the electrical leads. Well i unhooked the AC temp sensor on top of the thermostat housing (its for the auxiallary fans) and bam....engine started.....and again it started....hooked sensor back in..no start......took it out..it started...so i decided to put everything back together (covers etc)..then went to start car again....bam...nothing...just starter turns, flywheel turns...no fire, hooked sensor back..fiddled around a bit...still nothing....so tommorrow i will try your trick with flicking the top of the relay, but any other advice would be useful. thanks once again

the tired and confused j-mang

 

As earlier suggested i tapped on the relays as the engine was being started, and alas after flicking the fuel pump relay, the engine fired up. Currently going to replace that relay along with the temp sensor i mentioned earlier (it was partially broken) Now am i correct in saying the fuel pump relay also controls the auxiallary fan sensor as well? (I.E. The sensor i will replace)? Should i also check wiring to that relay unit? Any other information that will help is very much apprieceited. THanks once again.


j-mang

 

Turns out it wasnt the relay but the connection wires were loose causing loss of power to relay, gonna try to secure those and see how we go from there. ALl in all I think i can safely say the car runs now.


j-mang