hey im new here,also new to diesels and mb. bought a 1985 300d with 169,000miles on it a few weeks ago . org owner,sitting up for a long time. changed fluids hoses, belts. its running good. the question i have is i want to add an electric fuel pump about 10 psi before the lift pump to help take the load off the stock one,and also might try wvo in the future and this would help with that. my problem is where do i connect the positive from the pump to? i want a hot wire tied to the running of the engine and turned off when the engine stops, theres no ignition wires so where would i tie into? thanks for the help mikemike

There should be a small clear filter close to the stock fuel pump on the IP - that would probably be the easiest place to install an electric pump up front.

I don't know why you'd bother with one on normal diesel though - but hey ho if you want to play - have fun!

As for asking about WVO (can be dangerous here) there's an alternative fuel subsection to the diesel discussion where you can get that kind of information

Alternative Fuels - PeachParts Mercedes ShopForum

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

thats about where i was going to mount it. im just trying to figure out where to get the 12 volts that is on when engine is running and off when engine is off, if it was gas i could pick it up at almost any ignition hot 12v. thanks

An electric fuel pump is useless and in conjunction with the normal pump it would lead to higher load (the electric pump pushes against the piston movement of the mechanical fuel pump).

If you do want the electric fuel pump, you can use a wire from the glow plug relay to power a relay which powers the fuel pump.

I would add a hobbs switch T'd into the oil pressure sending line so that it would close the circuit when the oil pressure is up and open it when the engine is off. If you were real slick, you could make a bypass circuit that ran the pump for a few seconds every time the key is switched on.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Using an oil pressure switch would keep the pump on when the engine is running. The cranking bypass could be accomplished by wiring a relay coil to the starter crank wire and the contacts to power and fuel pump.

If you are using the solenoid type pump, they will stop pumping when dead headed so no worries about running to the stock lift pump.

On mine the Cigar/Cigarette Lighter circuit comes on when the Ignition is turned on and it likely has a Fuse with a High enough amperage for an Electric Fuel Pump; but check your Fuse Chart to be sure.

I think if you were going to use a Electric Oil Pressure Sending Unit you would need to set it up so the Sending Unit activated a Realay and then the Electric Pump would go on.
But, that would mean the Electric Fuel Pump is going to lage behind during starting.

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84 300D, 82 Volvo 244Gl Diesel

Pump to be of any real benefit running alternative fuel has to be at the rear of the car.

thanks for the replies guys,kartek what is a hobbs switch? do you need a relay with it? also by not dead heading the pumps do you mean the electric pump wont fight against the stock pump while running? also why is it better to put the pump by the fuel tank instead of under the hood ? thanks, mikemike

Hobbs makes pressure switches. You can get one set to about 10 PSI, normally open circuit and that should work for you. As stated above, you could also hook a power wire to the starter circuit to run the pump while cranking.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Many types of fuel like wvo have greater viscosity or thickness. Not unusual to have a booster pump for them near the fuel tank.