‘70 W114 114.023 250C Fuel System Pump - PeachParts Mercedes-Benz Forum

mercifiknow · #1 11-06-2021, 12:31 PM

Disclaimer (again): I’m new to Mercedes and mechanics so be gentle :-)

From my previous posts my fuel system is full of trash and I’m not able to take off my gas tank yet. There is a micro fuel pump in the engine bay. I will run the fuel line to my makeshift gas tank and run a little fuel through it and clean the micro fuel pump out with new filters before and after the pump.

But my questions are what is normally in the gas tank (Bosch fuel pump?) and why would they put that micro pump in the engine bay?

Frank Reiner · #2 11-06-2021, 02:31 PM

Quote:

Originally Posted by mercifiknow

Disclaimer (again): I’m new to Mercedes and mechanics so be gentle :-)

From my previous posts my fuel system is full of trash and I’m not able to take off my gas tank yet. There is a micro fuel pump in the engine bay. I will run the fuel line to my makeshift gas tank and run a little fuel through it and clean the micro fuel pump out with new filters before and after the pump.

But my questions are what is normally in the gas tank (Bosch fuel pump?) and why would they put that micro pump in the engine bay?

The OEM fuel pump was a mechanical pump, mounted on the left side of the engine block, below and roughly in line with the distributor. It was actuated by an eccentric on the oil pump drive shaft.

The electric(?) pump you have discovered is used as a substitute for the original mechanical pump.

mercifiknow · #3 11-06-2021, 05:45 PM

Correct Frank. it’s electric.

Is there anything in the tank like a sending unit (I may be showing my ignorance here!)? I’m assuming electric is better (reliable) is probably why they replaced it?

I would like to put the OEM mechanical back on it if possible. Are they easily found?

Frank Reiner · #4 11-06-2021, 06:59 PM

Quote:

Originally Posted by mercifiknow

Correct Frank. it’s electric.

Is there anything in the tank like a sending unit (I may be showing my ignorance here!)? I’m assuming electric is better (reliable) is probably why they replaced it?

I would like to put the OEM mechanical back on it if possible. Are they easily found?

There is a sending unit in the tank for the gauge.
The OE mechanical pump was constructed of nonavailium; hence the presence of the electric pump.
A better location for the electric pump would be immediately adjacent to the tank.

mercifiknow · #5 11-06-2021, 07:33 PM

Lol

I’m finding some on line. I’ve got a while before I’ll get it as right now I think I need a tank and really need my rockers replaced first. I will look to move closer to the tank though.

The pump is Mercedes made by Bosch correct? Has Mercedes name on it? Is Sending unit made by Bosch?

Frank Reiner · #6 11-06-2021, 08:07 PM

Quote:

Originally Posted by mercifiknow

Lol

I’m finding some on line. I’ve got a while before I’ll get it as right now I think I need a tank and really need my rockers replaced first. I will look to move closer to the tank though.

The pump is Mercedes made by Bosch correct? Has Mercedes name on it? Is Sending unit made by Bosch?

The OEM mechanical pump was made by Pierburg, and labeled as such. That would be the first choice of aftermarket brands; avoid MTC.

cth350 · #7 11-06-2021, 09:06 PM

If you have bypassed the fuel tank, pay attention to what happens with the fuel return line from the carbs. The idea is that at idle, there's a constant circulation of fuel to the carbs and back to deal with vapor lock. Once the car's moving (engine load rises a little), that little return valve closes.

An electric fuel pump can provide a huge amount of fuel quickly, so be careful what you install. If there's a way to bleed excess pressure back to the tank, consider doing that.

-CTH

Idle · #8 11-06-2021, 09:20 PM

A friend of mine had an old Chevy truck and the fuel pump went out. This was a mechanical pump but it was difficult to line up the pump arm when installing the new pump.

So he gave up, bought a plate to block the OEM fuel pump opening, and installed a small electric fuel pump. He also put a fuel pump regulator in line after the pump and before the carburetor. I don't know if this was necessary. At the time such regulators were being hyped as a fuel saving device.

So many years ago this was a common fix. The previous owner probably saw the price of a replacement OEM pump and the cost of a small generic electric pump and decided all they wanted was for fuel to pump. So they went the cheap route since it worked.

There are, off and on, rebuild kits offered for the OEM pump. These kits seems to come and go from the market so you can look around and might run across one currently for sale. Rebuilding the OEM pump is pretty simple if there is no mechanical damage.

Mike D · #9 11-06-2021, 11:23 PM

One caveat to using an electric fuel pump is they will continue to pump fuel as long as the ignition is in the #2 or "run" position regardless if the engine is running or not. I strongly advise installing a "fuel cut-off" switch to avoid this.

mercifiknow · #10 11-07-2021, 12:27 PM

Frank- I’ll be on the lookout for them.

CTH- I’m leaving the opening a tiny bit loose for pressure. I’ll add the return line though.

IDLE- I did see on a couple of videos someone doing the exact same thing. My electric pump has a regulator on it and I did see some rebuild kits yesterday while investigating based on the information here in this thread.

Mike- I bought some cut off switches the other day for that reason.

I DO appreciate the help in this. It’s complicated and dangerous if you don’t know what you are doing. My only goal right now is clean the carbs, keep engine from damage, and move it 100’ or so (no way am I driving that car other than driveway).

Today I finish the carb’s and hopefully hook everything up.