Fuel Pump compatibilities.

[SteveDuNord]

I've managed to snap off a lug from my brand new Bosch fuel pump and will need to solder it back on. In the meantime I'd like to fit a cheap pump.

The problem is finding one that is compatible with the car (1977 280se)

Flow rate on the Bosch is 200l/h at 5bar. The recommended alternatives advertise a range of flow rates at various pressures.
(the pump the current version supersedes ran at 165 l/h).

My question: do I have to buy one running the same specifications as the Bosch unit?

[andrewk]

The fuel system is one of the most important parts of your car and the pump IS made by Bosch for the Bosch injection system....
The key piece of information is the delivery pressure. Constant fuel injection (K-jet etc) requires a stable, high pressure fuel supply in order to correctly fuel the engine. The fuel pump isn't too expensive (e.g. https://www.ecstuning.com/b-bosch-parts/electric-fuel-pump/0020919701~bos/ - I assume this is what you broke?). Given that the Bosch pump will last a very long time, i'd just bite the bullet and don't cheap out on such a crucial piece of your car.

You should also change the filter, flexible hoses and pressure accumulator while you have the fuel pump assembly out of your car - if this stuff hasn't already been done. You should check and replace the filter in the fuel tank too, and thoroughly inspect the system for leaks and damage. Remember, fuel is highly flammable, explosive without much trouble, damaging to rubber, plastic and your health - and has a tendency to leak out of things pressurised at ~5 bar.


A

[SteveDuNord]

It will break my heart having to replace a brand new pump, like for like. But I suppose then I could repair the other one and store it away.

With the flow rate of the pump that preceded the current version being different, there surely must be some leeway involved? I am clueless on such matters.

[raueda1]

If I'm understanding you right I wouldn't worry about it.  I'm not sure about the significance of the 5 bar pressure spec.  As flow volume is reduced by the FD pressure goes up.   The diagnosis manual specifies a flow rate of 1L/30 sec from the return on the fuel distributor and doesn't specify pressure.  Looks like your pump candidates should exceed that by a wide margin unless there's a restriction someplace. Then, what matters is being able to achieve the correct system pressure (~5.8 bar if I recall).  I can't imagine any of these pumps not doing that if they're designed for the K-jet system.  Others may comment further cause my understanding of it all is still rudimentary.    Cheers,

[revilla]

Hi
I love when we entered into the what-if zone to evaluate options to keep our cars running. Purists might be uncomfortable, but one day or another we'll have to make choices if we want to keep our machines running.
@Steve: just a couple of things to check.
1) you have a CIS in your car, meaning excess of fuel will be returned to the tank and only the needed by the injectors will be used. Of course that's variable by demand. So putting a pump with higher flow rate won't cause any problem. Unused fuel returns back to the tank, no issue, no mystery there as long as your proposed pump has equal or higher flow rate.
2)BUT system pressure it's important, not critical but important. Luckily you have and you have already played with your pressure regulator on the side of your FD. You have a pressure gage if I remember well. When you install your new (more affordable) pump you can play with the shims and spring to get the 5.8bar system pressure needed. But as said, there's some tolerance there for SP. Not the case for CP which needs to be dialed in with precision according to ambient temp........ well you know the WUR music already.
Good luck.
Let us know if we can help further.

[SteveDuNord]

I just ordered a generic one from ebay - the only source in the UK - to get it here faster. Wasn't even that cheap lol.
Let's see if it works!