Exactly how does the dual fuel pump setup work? I'm installing a wireless immobiliser which is designed to take the fuel pump out but as I have 2 it'll take a little thought! Will taking 1 out prevent the car being started? If not then are they active simultaneously always or is there ever a time when just one if left on (perhaps at idle)? If they're both always on I can get around it with some relays . Thanks

I had thought one was only used under high load... but since my 86 3 liter only has one pump I never paid much attention. What about disableing the FP relay power supply?

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

I think in the end, this is what you would need to do to disable the pump(s) as the FRP powers them up.

On your model it should be easier as the FPR is a stand-alone unit, unlike those built into a MAS unit.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

It's not as if the pumps are fed from two separate electrical circuits.

You have a fuel pump relay conveniently located near the battery.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Who steals 300Es?

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Auto Zentral Ltd.

Fuel pump relay would be the most convenient point to immobilise it from. All done now though . You can never be too secure, I guess a tracker is best though. I've seen a shocking number of neighbours cars 'dissappear', returning only as they were tracked. Thieving scum .

autozen, it's a Brabus 3.6 but I posted under '300E' as the fuel pump arrangement is the same. Interestingly (and very unfortunately) though in and around the London lots of W124 and W123 Mercs were stolen by a gang(s?) who broke them and sent them off to Africa so I feel doubly threatened.

put a "return to" sticker on the engine and put my name on it. I am so jealous.

That clears that up. You didn't say where you were. We don't have a problem in California. Here they steal Hondas. The fuel pumps are run by one relay.

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Auto Zentral Ltd.