erratic fuel gauge.. help

[jarance]

Theorectically, a fuel pump is a fuel pump. However, we have to consider whether the pump is design to be mounted inside the tank or outside the tank. Fuel pump that are designed to be mounted inside the tank have to be petrol proof. i.e. petrol should not be able to get inside the winding of the motor and cause a spark. The consequence would be explosive to your tank.

Another thing to consider for the pump is the flow capacity and head pressure. If the flow capacity is low, then it will not be able to deliver the required amount of fuel to the fuel injectors at high speed. Similarly, the head pressure also play an important part but there should be a pressure regulator to release excess pressure if the head pressure is too high.

Hence, it would be sensible to use a bigger capacity pump rather than an undersized pump. However, you have to consider for the constant working of the pressure regulator.

So far, the fuel pump is working well but there is nothing like a piece of mind when you used ori parts from BMW (Borsch).

 

[loner1my]

hi guys... i run out of fuel without any light warning and with a reading of a quarter left on the gauge.... i used to go to the nearest pump whenever the low fuel indicator lights up.... now i am told that to eradicate the problem, change all the parts; the 2 fuel floats, carbon tank and the breather valve... the most likely faults are the fuel pump float and the carbon tank.... a friend of mine told me its rubbish, and that i should only changed the fuel float ( the 1 without the pump), since the reading is faulty... pls advise as i wouldn't want to change anything unnecesarrily...

 

[tank34]

loner... just changed my float and float/pump recently. Resolved problem instantly. May I suggest that you do one at a time. Just change the left sided float first to see if it fixes the problem, if not then replace the float/pump combination on the right side.

You'll be making a guess actually, and I only suggested the float because it is cheaper to replace. For all we now, it could be the float/pump on the right that is the problem.

I should have saved both my float and pump so that you guys can use it as an experiment. I suggest you do the same.

 

[loner1my]

yea, tank34, reckon that's what i'll do thank u all the same...

 

[calyon]

only thing to add.. u may ask ya mechanic to TEST both floats to see which is the LIKELY spoilt unit then change that side 1st (sometimes not necessarily the Left side coz the Right(with pump) also got the tendency to fail early). after that, if it doesnt solve even with a new float then change the other side too. this way, sure cant go wrong lor..

 

[loner1my]

yes calyon... i agree, but to do the TEST, i'll need to know the RESISTANCE VALUE for full/three quarter/half/quarter of the fuel reading... jarance mentioned 10 - 150ohms, hope that he or someone can fill me in?!... thank u

 

[jarance]

yes calyon... i agree, but to do the TEST, i'll need to know the RESISTANCE VALUE for full/three quarter/half/quarter of the fuel reading... jarance mentioned 10 - 150ohms, hope that he or someone can fill me in?!... thank u

aiyo, just measure the resistance when it is fully down and when it is fully up.

if the minimum is 40 ohms and maximum is 200 ohms, then 25% = 80 ohms, 50 % = 120 ohms , 75% = 160 ohms.

resistance value (%) = % x (resistance at max - resistance at min) / 100.

Another thing to consider is to compare the reading between the left and right sender. It should be about the same value for the same amount of deflection.