Fuel pumps

[Picadilly]

I know i need an electric fuel pump, and i know my mini has a mechanical one. Basically im just wondering what the difference is? Do i have to remove the mechanical pump to fit the electrical one properly?

[Geehawk]

Your mechanical fuel pump is attached to your A series engine and will go when the engine does.

The electric replacment one will either fit inside a modified (or injection) fuel tank or outside of a modified tank. The tank will need a feed and return. The pump must be able to supply something at around 3-4 bar IIRC. You will also need a filter to stop the crap in the fuel knackering your nice electric pump. I have used the metro item under the bonnet, and a Metro gti pump fitted inside a mini injection tank.

[Picadilly]

Lol, ok. Hehe - i like the it's attached to the engine bit :D

Right - other random query - why would an engine want to return fuel to the tank? wouldn't it get burnt or pour out the exhaust?

Will the mini inj pump do the job or not?

[Geehawk]

The fuel return is needed because of the way fuel injection systems work. The fuel is pumped under pressure (much higher then your mechanical setup for a carb) to the fuel rail, where a pressure reglator limits the pressure to a certain figure. Obviously the amount of fuel being pumped into the system is much more than the amount getting injected into the cylinders and so this excess fuel is fed back to the tank via a fuel return.

Basically its all to do with the pressure. Your mechanical pump fills the float chamber until the little valve thingy (not getting too technical I hope :wink: ) stops more fuel entering. The pump being so low pressured keeps pumping away, but the valve stops more fuel entering, but its all low pressure and quite safe. Injection pumps if they have no where to pump will keep pumping until something in the system gives and you get fuel everywhere. It wont get burnt as its not entering the engine, likewise it wont pour out of the exhaust........

I believe the mini injection pump will work for a Single point injection engine only. The Mpi will run, but will not get enough fuel under load.

Anyone else please point out if my understanding of all this is completely wrong.

[Picadilly]

Right, that makes sense - I suppose the clever thing to do would be to fit the pump and sender from my donor car so the engine works properly and the fuel gauge doesn't lie like the one in my old metro!

[strudel]

Best keep as much mechanical from the donor as possible. Makes life easier in the end and harder in some other aspects. The more of the donor you can keep together saves the grief of having to build a one off part or make a new electrical connection up. This is what happens in the Honda swap world. They swap a different engine into their own car but have to either change from carb to MPFI or even DPFI to MPFI. Other problems they incur which will happen in the Mini world are the axles hubs, etc. The biggest obstacle in most cases is the wiring because of different ecu's and the oem wiring to the new insertion. I don't know if this helped any but just are some general comments to think about. JS

[Picadilly]

so do I have to modify the metro pump to fit into the mini tank and work properly or is it a straight bolt in jobby?

I'm most concerned about the shape of the tank affecting the internal pipework length[/i]

both my metros only had one pump, that was in the tank, so does the gti have an additional pump under the bonnet then, sounds like the pump in the tank is a standard unit and the additional is required due to the multi point system.
sean.

[Geehawk]

The Gti just has an uprated "higher pressure" pump in the tank. I fitted it in place of my SPi mini pump with a jubilee clip. :wink:

[MM-Mad]

Most SPi systems run between 1.0-1.5 bar pressure. (15psi-26psi approx). But MPi systems usually run 3.0 bar or slightly above. (35 psi)
You coud run the Metrot MPi pump in the Mini tank (if physical space allows) or run an external (gravity fed- lower than the bottom of the tank) MPi pump- similar to VW Golf GTi's late 70's-early 90's/Vaux. Cav/Astra-early 90 era.
I think (from memory) the twinpoint/later Mini runs a high(er) pressure pump.

[evolotion]

i fitted my rover 400's pump to the pickup pipe in a normal mini tank useing a jubilee clip also! should be a pic in teh gallery. uploading the now :)

[Picadilly]

ok, metro pump bolts into mini tank, i already knew this, but my problem is do i have to modify the internal pipe work so it reaches the bottom of the tank or will it be okay as it is?

Maybe i worded the question wrong.... :P

[Picadilly]

evo - im assuming thats outside a non injection tank?

i have the injection tank - do i just whack the metro pump on the bottom of the mini pipes inside? also the wireing has a different connection method - call me silly but surely a electrical connection in the fuel tank is asking for trouble?

this really has me scratching my head now - any ideas greatfully received :)

[evolotion]

electrical connection in the tank are fine. just make sure its well crimped / soldered. and (as suggested by geehawk) sit your intended wire and conectors in a bowl of petrol to c how they fair before useing them.

That is a normal mini tank modified with a big hole in teh top of it for me to get my hand in. fraid i cant help you wiht the injection setup, but IIRC there werre quite a few pics posted in teh honda section.

[Geehawk]

Mine was a SPi mini tank. IIRC I did nothing to the pipe work, just a jubilee clip to hold the pump as it doesnt fit the bracket, and the mod to the wireing that you mentioned.

Stupid as it sounds wiring in the tank is fine. There is a technical explanation as to why, but I dont understand it.

I defy you not to wince when you start it up first time though :lol: :lol:

[trickey]

I'm using a fiesta pump, same as the VTEC lot use, but only 'cos it was available at the right price (ebay!) I had to shorten the pipework in the tank slightly and use a short length of hose and 2 jubilee clips to hold it together. there are several threads in the honda section about this.
on the subject of wireing in the tank, make sure the wires you use are suitable for immersion in petrol, same goes for any terminals. The petrol could rot the insulation, and that wouldn't be good :shock:

Edit: Doh! i shall read the whole thread more carefully in future :D