25 replies to this topic

[mick black]

I have a Mpi with a stage 3 head, sw5i cam and k&n and the 48 mm alloy throttle body

I get really bad MPg driving around town. However I get bettter results on the motorways

I think I average around 180 on a full tank. 24 litres mine is.

Mike

what size tank do you have?

[Sprocket]

There is always more fuel in the tank than you think. The late mini tanks are 7.5 UK gallons which is roughly 34 litres, and if you run the tank dry you will only ever squeeze 32 litres in there because of the air gap at the top of the tank.

when the needle is reading in the red there is at least another 5 litres still in there. EVERY car does this, its called the reserve. You look at the gauge and think you are going to run out, so you fill up, thus preventing you from running out. So, if you do run out, you have either run out of fuel on purpose, or you have ignored the reason the fuel gauge is there and its your own fault excepting genuine failures of the gauges

[dmdangermouse]

It is abit annoying though.
Is there anything to adjust so the gauge reads the true amount?
I think it would be better than guessig.

[Sprocket]

I have told you that there is about 5 litres in the tank when its in the red. how are you guessing now that you know this?

When its in the red, fill up. Simples

If you decide to use the reserve without any indication, that is your own risk. All cars have this, its nothing new, its just that the mini tank is so small compared to most modern small cars

[rick.spi]

i recon no mini can be as bad on fuel as my 1.8 focus its a *melon* engine it uses loadsa fuel and aint particualy quick, cant wait to get back to mini fuel economy

[dmdangermouse]

the most i have ever done is about 130 miles, and that was taking it real steady down to cornwall. With my guage, it is completly empty as soon as it hits the red line, is that good??

It seems that people are getting different readings.

[Sprocket]

You will always find conflicting evidence as there is always the human factor that never seems to be taken into acount in these situations.

What is to say the last owner is thinking along the same lines as you and has bent the arm on the sender inside the tank so that it reads the dregs in the bottom of the tank when its too late and you have run out.The rate of the gauge changes with the level in the tank, thats just physics, the tank is an odd shape. a bent sender float arm will read lower further and quicker and full longer. There could be fuel in the float, and the stop adjustment of the float arm on the rheostat could have been tampered with. too many variables that the sticky fingered people can play with. Then there could just be the faulty or mal adjusted ones that have allways been like that. The majority of fuel gauges will read as they should.

Of all the minis I have had, carb or injection, it has been no different.

MPG using the mini clocks and the inacurate measuring by filling the tank once does not give you an acurate MPG figure. You need to do at least 1000 miles, and brim the tank to the exact same level every time and record the odometer reading which has been calibrated. Tyres, brakes, tracking, wieght all have a bearing on the final result and not nescisaraly a problem with the tune of the engine, although a combination of them all is not going to be obvious whats wrong.

Also note that there is another valid reason for there to be a reserve of fuel in the tank, and that is to stop the pump running dry. The pump does not sit right on the bottom of the tank.

[Ethel]

The fuel sender is a variable resistor worked by a float on the end of a "coat hanger wire" arm. You could easily bend the wire to adjust it. It'd only change the start or end point though, not the rate at which it moves.

[dmdangermouse]

I guess it also saves all the crud being put through the system aswell.
I always thought my dial was 'off' because when i brim it, it never reaches the black line on the dial.
Mr Sprocket you seem to really know your stuff. How long have you had an mpi?

[Sprocket]

If you bend the arm to read lower in the tank, it will read full with less fuel in the tank also. When the tank is brimmed, you will need to use more fuel before the gauge starts to drop, therefore it will read full for longer

As for crud, what sort of crud? Water will sit at the bottom of the tank, as will any dirt. Anything that is light enough to sit ontop of the fuel will be 'screened' out before the pump, and anything that does get through will be filtered out before it reaches the injectors.

'Crap in the tank' is an excuse used by garages as an explanation to a problem that they cannot easily explain. All the petrol tanks I have looked into, have been clean in the bottom.

Fuel contamination is different, lots of water will obviously cause a problem and silicone will damage the lambda sensor and cat (Tesco)

Edited by Sprocket, 21 January 2010 - 11:19 PM.

[danrock101]

hmmm well I always used to think I had plenty of fuel left untill one day going up a hill I ran out of fuel now I top it up asap