Fuel Problem

[MrNutter]

So I've got a weird fuel problem with my Series 1. I can park the car with the gauge reading at one spot but when I get back in it the next day the gauge will read significantly lower than when I parked it. The gauge actually drops by up to 1/8 of a tank while the car is just sitting there. The gauge is accurate, that I know for sure. On top of that while driving, if I give it a bootfull, the gauge will drop by the same amount & not come back up. I replaced all of the rubber hoses going to & from the tank about a month ago, I replaced the O2 sensor last week & I thoroughly checked the tank for leaks & cracks when I had it out to do the hoses. I've checked the return line & throttle body & as far as I can tell there are no leaks or cracks anywhere. There is no evidence of fuel leaking under the car or on the floor of my garage where the car is parked overnight. I've had this problem for about 3 months.

Where the hell is my fuel going?
Any help would be appreciated.

[Brett_jjj]

It sounds like the fuel gauge sender in the tank is getting stuck or is sticky.Id remove the sender unit from the tank and check it out or maybe even replace it..

[vnstu]

mine does the same thing.

when i put fuel in it it seems to come back up to where i expect, so i figure i'm not loosing fuel. bashing the cluster will sometimes give me a bit more fuel too.

i figure it's nothing serious...combination of dodgy sender and gauge...

[MrNutter]

Problem is the gauge is accurate. It's empty when it says it's empty & full when it says it's full. I've filled it up from various levels & taken note of how many litres I've put in, each time it takes the amount I expect to have to add to fill the 63lt tank to the first click of the pump. I've run several fuel economy checks on it over the last few months, 26mpg up from 18mpg before the O2 sensor was replaced. I've checked the gauges accuracy every way I can think of & I'm certain it's accurate anywhere between empty & full. This thing is actually losing fuel out of the system somewhere but there's no smell or evidence of a leak anywhere.

[92 VP SS]

My V8 feels like it loosing fuel too ! Sometimes I think its in my head. My theory on the gauge is once the needle is up it goes down easily say you go around a corner fast or accelerate fast it will rapidly drop but its harder for the needle to go back up to the original point so it settles at a lower point .

I would really like to wire my fuel gauge so that its on all the time that way it wont drop down so far and have to painstakingly climb back up again.

In summary I think that the needle cant climb back as far as it drops especially below the 1/4 mark also I think the whole sender/gauge system is weak the worst fuel gauge Ive had, christ my 1964 Mk1 cortina gives quicker readings !!!

I took mine out the other day and cleaned the rester pin as it was sticking to the needle and causing it to be even slower !!

[yogi_b]

I suspect that this may potentially be a similar problem as with the fuel gauge/temp gauge not working due to a dry solder joint on the voltage regulator (see the sticky here Solution to Sticky fuel/temp guages).

It has been happening to my car for quite some time and like vnstu said, bashing the cluster can help the gauge settle. I suspect that the dry solder joint is allowing some, but not enough voltage through to drive the gauge accurately and hence it settles lower than its supposed to. I'm going to tear out some wiring and re-lay it this weekend and will have a crack at fixing that dry solder joint (sick of having to bash the cluster to get an engine temp). I shall let you know if it makes a difference on the fuel gauge accuracy

[MrNutter]

Thank you all for taking the time to reply. I do feel though that I need to reinforce the point that the gauge IS ACCURATE. I'm used to giving it a belt to get it to come up that extra little bit & it it still reads significantly lower than when it was parked. This is actually fuel dissapearing out of the tank/system, mainly overnight but also while driving using heavy acceleration.

Thank you again for taking the time to read & reply to my question but I think I'm really after possible places that the fuel system could be leaking without being easily noticed.

[Brett_jjj]

If you are loosing enough fuel to notice it on the fuel gauge,then its not going to be a small leak thats hard to notice,its gonna be running out onto the ground.And it wouldnt evaporate away that quickly that you wont notice it either.Someone might be knocking it off,either that,or its just a sticky sender unit in the tank..Ive seen a few of these gauges show one level at one time,then next minute they are showing a completely different level and so on.

[VNVacationer]

If you are convinced its not the gauge and you have already done an external leak test by pressurising the system (without running the engine). Try the internal test. Maybe one or more of the injectors are leaking , although I would not think you would lose the amount of fuel your talking about this way as it would show up via oil dilution, excessive fuel comsuption or something but an internal test would be the next step as that will tell you for sure if there are problems.

[yogi_b]

I know you're sure that the gauge is accurate, I'm just reporting back on my findings: Re-soldered the voltage regulator and now my fuel gauge is showing consistent levels of fuel when before it wasn't. Also don't have to bash the cluster anymore for my fuel level and engine temp, bonus!

[MrNutter]

Glad you got yours sorted yogi_b. I seem to have sorted mine out to by replacing the return line. I don't know why replacing that has fixed the problem because I can't find any signs that it was leaking anywhere & there was never any fuel under the car or stains on the ground where fuel was leaking. I got given the new line so figured I might as well fit it & the problem seems to be fixed. I'm not going to worry about the why though, it's fixed & that's all I'm really worried about.