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1994 Mercedes C280, 1971 Camaro SS
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5 Posts
Discussion Starter #1
I found my 94 C280 in a warehouse after years outside (6 yrs) of sitting. It did not run and looked awful. after washing it and cleaning it out, it look great with some repair. I read and troubleshooted this car before I decided to replace the two fuel pumps. I bought one from O' Reillys and ordered the other one. when it came I had some trouble with some fittings so I just used one of the fuel pumps and it came alive!!!! I let it idle for about an hour checking things and it sounded great. I some unusual noises like the whining of that fuel pump.

It came to me that this should not be making this noise. With German engineering in mind, I know it should not be making this noise, along with a pulsating noise in the engine.

Questions: Why does the 94 use two fuel pumps and should use both of them?

Does the fuel pump run continously, (reason for the whine)?

I havent taken it for a road test because it is not insured or registered yet so I dont know if it has effected the performance. I am a Chevy guy so my knowledge of the MB is not extensive but I got the MF running. Thanks for any input on this matter.

Bobby
Platte City, MO
U.S. Army (Retired)
[email protected],com
 

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2010 E350, 2005 Tundra Sold the 1998 C230
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322 Posts
Bobby
I have a 98 c230 and got the alldata subscription for it, good to have some sort of manual for these cars, they are quite different from fords or chevys in how they engineer things. Just about everything is computer controlled like power windows for example. From reading on my car, there are some references to two pumps being used to make a 2 stage fuel pump and that they were later changed to a "Screw Spindle Pump Replaces Double Fuel Pump Unit" . Not sure if it is designed to run all the time, but it is remotely controlled and has to provide adequate pressure at the rail. From what I can see, there is one entry for a double pump listed and that was up to 1993. Guessing the 280 needed the greater flow rate.

6 years sitting? Wow, thats a long time, especially if it was outside. I would get every fluid in that thing changed out asap before it gets on the road. Plan on lots of the rubber and plastic parts being dried out too. Tires would need to be replaced even if they have decent tread left.

On the positive side, these are very nice, solid little cars that are actually designed with service in mind. I enjoy driving mine, brings a smile to my face every time. Good luck with it, post some pictures and keep us appraised with the progress.

Bob
 

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1995 C220
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2,800 Posts
I didnt read the manual so take this for what it is worth, but I would assume they would run all the time. fuel should run from the pump up to the fuel rails. Somewhere in the fuel rails there should be a pressure regulator that keeps the fuel pressure at (guessing) somewhere around 50-60psi. If it builds any more pressure than that the regulator lets the excess fuel past the regulator into a hose that dumps back into the tank. So based on that, fuel pump should run all the time, with the exception of when ignition is on and engine is not running, in this case the computer system senses that engine is not running or even being cranked yet and will kill the fuel pump.

This is an educated guess, but I'll try to look at my cd tonight and verify that.
 
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