Hi guys,

I'm new at this. I'm in desperate need. I have a 1991 420 SEL I was told the fuel pump may need changing. This car has 2 fuel pumps on it. We have already changed the fuel filter. How do you know which fuel pump to change? The car will begin to jerk and then it will just shut off. Is this a fuel pump
problem??

I will apprecitate all the help I can get, Oh Yeah can you tell me if both of
these pumps are in the front.

Thanks a lot

Don't know your chassis, but if it's like mine then your fuel pumps are by the right rear wheel. Possibly with a plastic cover over them. If you put a hand on them you can feel them running if the engine is running.
Couldn't tell you for sure if that is your problem though.
Good luck.

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84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

If both pumps are original then they "should" be replaced as a pair. MANY times we would replace 1 & with-in a few days the other one would quit.
MOST of the time that requires a TOW & a very un-happy person...

MB part number WAS 002-091-88-01 & can be replaced by 003-091-53-01.


They are at the rear of the car on the passenger side in a plastic housing.

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Retired Moderator

You can run a pressure test with a special MB tool and a pressure gauge to determine which pump isn't working to specs, however, this test was only designed to determine premature pump failure when the pumps are relatively new. I would follow the advice biven here by others and replace both pumps if they have been in service for a long time. That being said, you need to determine if the pumps are really at fault. Testing these pumps is not an exact science even though the book says it is. If the pumps are noisy they should be replaced. Also you can hook an amp probe around the wires and read the current draw and wave form of each pump. This is not a foolproof test as I found out. I had a 300E that died on the road and was towed in. Ran great in the shop and on test drives. I discovered no current flow through one pump. I tapped it with a hammer and it came alive with a jagged wave form. I ordered new pumps. When they came, I checked the currnt pattern again just for *****s and giggles. The pattern and current draw was perfect on the failing pump. The conclusion is that if the pump fails any tests you've discovered the problem, but if it passes the tests, you still don't know. Also there are pressure and volume tests. You may want to seek out a professional before you spend money you don't need to. Good luck.

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It may well be the (in)famout OVP relay or the fuel pump relay. MBZ electronics mfg must have been subcontracted to the SKODA works in Poland or? They are real trash, failure prone due to faulty solder joints of all things.

Check out the relays before replacing the fuel pumps--which don't usually fail at all.

Pardon me, but where did you get the idea that the fuel pumps don't usually fail?

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Auto Zentral Ltd.

fuel pumps never fail? the fuel pump on my 300E doesn't even like getting hot. after 90 minutes driving it starts buzzing and the engines starts behaving like its not getting enough fuel. and the pump's less than a year old, my third in two years.

and yes, it's a bosch unit, before anyone starts wittering on about pattern parts.

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1987 300e manual 250,000 km (sold)