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1989 560 SEL, 1993 400 SEL, 1986 420 SEL, 1977 450 SL, 1984 300D, 1981 380 SL, 1983 500 SL
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606 Posts
Discussion Starter · #1 ·
My 1993 400 SEL was running like S**T and I figured out that only one of my fuel pumps was working. It would idle fine and drive if I didn't get on the pedal real hard, but as soon as I pressed the pedal too hard, it would hesitate. If I drove it 30 miles or so, it would stall and wouldn't start until it cooled down.

While under the car, I figured that I would remove the bad fuel pump and run the line from the tank to the good one and run it that way until I got a new one, since I knew it was running on only one to begin with. Well I did this and to my suprise, this car runs fantastic! It goes like a bat outta hell. So, in conclusion, you only need one fuel pump on this car. If anybody is having similar problems with their early W140's, check your fuel pumps, one of them might not be working and if it isn't, it's like having a clogged fuel filter. I tried to blow through the fuel pump that didn't work and found it impossible to do so.
 

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2009 S550 4Matic,1986 560SEL, 1986 560SEL, 1992 500SEL, 1999 S500
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474 Posts
They put two on these cars for a reason. Many fuel injected vehicles have two pumps, even mundane ones like pickup trucks. It may not be readily apparent, but you may have problems later.
 

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Registered
1989 560 SEL, 1993 400 SEL, 1986 420 SEL, 1977 450 SL, 1984 300D, 1981 380 SL, 1983 500 SL
Joined
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606 Posts
Discussion Starter · #3 ·
Chuck, do you think that I will have a problem? My 450 SL has only one pump and the later S420's, S500's, and S600's all have one fuel pump. Both pumps run at the same pressure, so I don't understand why two are needed when they both run into the same, single line to the fuel rail.
 
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