Replacement electric fuel injection fuel pump

[Gregg Bambo Jr.]

The fuel pump on my 1963 6 cyl fuel injected M127.984 engine needs replacement. Rather than use an expensive 40 year old design original equipment MBZ pump, I was considering a relatively inexpensive modern aftermarket electric pump. The question is: What output PSI pressure and gallons per hour is the original, of which I would have to match? I can't find the specs anywhere in the maintenance manual. I am modifying the system to run one of two electric pumps that can are seperated electrically but can be activated by a flip of a switch in case of failure of either.

[Mark DiSilvestro]

According to my factory Mercedes workshop manual-

"The delivery PRESSURE, which is measured between the fuel filter and damper unit, should not be lower than 0.4 atm. with a minimum terminal voltage of 10 volts and an input at the feed pump of 3.1 - 3.5 amp.
When measuring the delivery AMOUNT the fuel tank should be at least half full....should be measured behind the return line damper unit, using a new filter element in the fuel filter....switch on the ignition for 1 minute. during this period, the delivery amount should be not less than 3.3 liters with a minimum terminal voltage (same as for delivery pressure test)

With my factory manual came some extra pages apparently torn from a Glens or Chilton Mercedes manual. They give these fuel pump specs -

For Engines With Two plunger Injection Pumps

Delivery Pressure 8.8 - 11.8 (0.6 - 0.8 atm) measured after fuel line filter.
Delivery End Pressure (minimum) 17.6 (91.2 atm) measured after return flow damper bowl.
Delivery Volume (in 20 seconds) 2.1 pts. (1.0 ltr) measured after return flow damper bowl, with fuel tank at least half full.

These old electric fuel pumps put out relatively low pressures, unlike the 50 - 60 psi pumps used in modern electronic fuel injection systems.

My Dads '60 220SE came with some sort of replacement AC reciprocating diaphragm fuel pump. It seemed to work OK but constantly made a muffled droning noise, like as if a propeller airplane was constantly flying overhead.

No ideas on installing TWO pumps. I'd prefer to keep it simple.

Happy Motoring, Mark

[Gregg Bambo Jr.]

Mark,
Thanks for the information. It was a real help. I'm installing the two pumps mainly for reliability in case one fails while I'm on the road.

[j9fd3s]

the early rx7's have external fuel pumps, and so will any cis vw/audi form the 80's.

if you want aftermarket, the walbro pumps move a lot of fuel but are noisy.

the external pump from a 930 turbo porsche moves a ton of fuel (enough for 500hp), but its gotten pricey

[wbain5280]

Don't forget, the fuel injection pump does all the heavy lifting, so to speak, and the pump delivers a volume of fuel to the injection pump.

So use a pump from a Suburban or other large engined American car. Remember, it's the volume.

[Gregg Bambo Jr.]

Having obtained and mounted a modern aftermarket electric fuel pump that produced high pressure and volume was a mistake. As forum replies stated, a replacement pump for a two plunger injection system has to be low pressure, large volume. After installation, the motor ran fine for a few days, then it started missing when cold and later missing at RPM's over 5000 and then missing thoughout all RPM ranges. Sputtered down to my old car guru's garage and he informed me that this particular motor will not run properly unless the electric fuel pump is an exact match to the factory original in pressure and volume. The high pressure was causing a problem in the injector pump and injectors. Pulling the plugs revealed all had sooted up. Installed a used original pump from a dismantled 111 and the engine started to purr again. We learn from our mistakes!