W108 1968 280SE Fuel Pump - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 12-12-2006, 11:17 PM Thread Starter
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Date registered: Jul 2006
Vehicle: 1968 280SE, 1978 250
Location: Brisbane, Australia
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W108 1968 280SE Fuel Pump

Hello all,

I have a 1968 280SE (W108) which is fuel injected. It is a project which I have been working on for the past 6 months and I have one last hurdle to climb before the car is able to be registered. The original fuel pump (part# 0442 201 002) is busted and needs replacing. There are about 6 variations of W108 fuel pumps, and I believe that 1968 was the only year that this particular fuel pump was used in W108’s.

I believe that there is 6.5 bar of pressure needed to open the injectors. My question is how much pressure is generated by each the ‘Fuel Pump’ and the ‘Injector Pump’ to create the 6.5 bar of pressure?

If anyone could let me know of any ‘technical information’, or the ‘pressure readings’ of these two pumps, I would be most appreciative.

Thank you for reading,
Sam Greenland
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post #2 of 6 (permalink) Old 12-13-2006, 05:04 AM
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You're in Brissy?,firstly ,is it the injection pump or the Fuel supply pump under the car?.If it 's the supply pump,what is wrong? is it pumping or not?.
The injectioon pump is a high precison item which believe me hardly ever gives trouble unless it's been interfered with.
Three Point servicesc in Mount gravatt are the only mercedes people in Queensland with the expertise and tolls to work on those pumps.
The injectors are supplied pressure from the injection pump.
The fuel; supply pump sends fuel from the tank to the injection pump which pressurises it.
There some Rules which you must stICk too when working on Mercedes MFI systems.First rule.NEVER LET THE LOCAL HOLDEN OR FORD MECHANIC ANY WHERE NEAR YOUR CAR!!!!!
2ND RULE.Start with the Ignition.it must be perfect.no ifs or buts,aim for perfection.

3RD RULE. Check compression. it must be a minimum of 150 PSI for the engine to even run half decent.

4TH RULE. Adjust the valves correctly on a COLD engine. Check the timing chain,any wear at all means time to replace it.Worn chains mean the engine will never run efficiently.

5TH RULE. the fuel filter must be replaced at least every two years.

6TH RULE. the pump is supplied from the bottom of the tank,replace both those hoses comming from the tank,remove the bung in ther center of the tank and get the filter in there cleaned ultrasonically.make absolutely sure the top smaller line is clear by shoving a wire through it.They rust up causing injection problems.

7TH RULE. The Pump MUST supply 3.3 liters in 1 minute AT THE COLD START INJECTOR. Any less and the car will never run right . delivery pressure is around 7 PSI. ignition on and engine NOT running.
toomuch pressure means a blockage in the return line to the tankl.in all probability you missed the blocked return pipe in the tank or didn't replace the rubber fuel lines and one has collapsed inside.

8TH RULE.For 100 liters of fuel add 1 liter of autotrans fluid to the fuel.it contains cleaning agents which keep the MFI free of moisture and varnish ( THIS ADVICE FROM DAIMLER CHRYSLER THEMSELVES ) .

9TH RULE .If the MFI pump has the dip stick,unscrew it and check if the oil is overfull,if so drain it out by sucking the excess oil with a plastic.

10th rule. Ensure that all the linkages are tight and you have no loose ball joints anywhere and that the throttle is colsing completely and not open when in idle positon.Idle is NOT governed by the throttle .

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post #3 of 6 (permalink) Old 12-13-2006, 02:10 PM Thread Starter
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Vehicle: 1968 280SE, 1978 250
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G'day Mercmad,

Yes I'm in Brisbane, I remember you helped me out with some information for my car months ago. Now the project is nearly finished after countless hours working on her. I have already got the safety cert. and insurance for the car (before this happened) and if all goes to plan, I will be driving her before Xmas.

The car is at EFI Diagnostic and Repair centre at Capalaba (they specialise in mercedes/bmw) and in the care of a very knowledgable German by the name of Jurgen.

Before I bought the car, it had been sitting in a shed for 4 years, and this was more than enough time for the fuel pump to cease working (the pump under the car down the back). The problem was diagnosed by Jurgen, and we have since been trying to obtain information on the pumps so we can find a suitable replacement. We can get a brand new genuine part, but this will cost $1068.50, and we are trying to find an alternative option.

Cheers, Sam
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post #4 of 6 (permalink) Old 12-19-2006, 11:15 PM Thread Starter
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Problem Solved!!!
The injector pump is the pump which produces the majority of the pressure (approx 15L per min so i'm told)- the unused fuel flows back into the tank via the 2 return lines. We have replaced the original pump with a new Bosch one and the car runs well. All that is left to do is fabricate some mounts to secure it to the bottom of the car.
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post #5 of 6 (permalink) Old 12-11-2013, 03:47 AM
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HI is it possible that the injector pump can be set to strongly. My 108 gets to much fuel and I sit with wet black spark plugs, some black smoke and the smell of fuel.
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post #6 of 6 (permalink) Old 12-11-2013, 03:21 PM
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That is usually one of three problem areas:

- cold start valve leaking gas into intake manifold
- warm running device stuck in cold position
- return line blocked

It's also possible that someone has messed with your pump linkage.

If you don't know what I'm talking about, suggest you find a mechanic who does.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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