Fuel Level Indicator Problems

I know that quite a few of you have had issues with fuel sender units etc, well now it's my turn!

Never had a problem with the fuel level indication until very recently. The trip computer now fails to register fuel being put in resulting in the low fuel warning light showing and consequently the 'SERVICE' flag being permanently illuminated. If I disconnect, and reconnect the battery, the computer does register fuel, and the warning lights don't illuminate unless I press the reset button after which it usually shows 0.0 gals and lights up the low fuel warning. The computer also fails to display the 'miles to go' readout. All other trip computer functions work.

Occasionally the computer does register some level of fuel - today we took the car (Le Mans) for its MOT and at one point on the road the trip computer indicated about 7 gallons, which then dropped rapidly through 5, then 3 and finally to zero as I watched it - the car clearly wasn't consuming fuel at that rate!

Before I start ripping things apart, does anyone recognise these 'symptoms', and have any idea what might be the cause of the problem? Looks like dodgy connections or a faulty tank sender unit - anyone know if the units are still available?

Many thanks.

Paul T

Paul check float wire has not snapped?
Note this is inside fuel tank, within sender unit.
I soldered mine back together.

Dave

Paul..... unfortunately there is no easy fix for this, only "process of elimination" I am affraid.
First I would do a full computor reset, ie:- Disconnect battery, hold reset button on rev counter for 20 to 30 secs, reconnect battery, switch on ign and push reset button once more. I have my doubts about this in your case but to be sure, it should be done.
If this does not cure fault, the boot liner will have to come out. Being the later type of fuel gauge, as well as the actual fuel sensor in the tank, there will be a TSU (Tank Sender Unit) mounted on the inside of the wheel arch.... item No. 327 in pic below.
Check and clean the connector pins on the TSU and also the connector No.199 on the sensor. Having cleaned them, Full Computer reset again (this should be done each time any of these connectors are disturbed and before each check).
If cleaning has not resolved problem, the sensor will have to be removed from the tank and checked with a meter. With the connections of the sensor upper most (float slides to the bottom... empty tank), the reading across them should be 85 ohms +/- 5, turn sensor upside down (float slides to other end... tank full) reading should be 2.5 ohms +/- 0.5.
If readings are not right, the sensor can be dismantled and visually checked. If you find the sensor is OK, then the TSU (327) will have to be investigated.
See how you go with the above before checking the TSU.
Hope this helps.

John

Paul..... unfortunately there is no easy fix for this, only "process of elimination" I am affraid.
First I would do a full computor reset, ie:- Disconnect battery, hold reset button on rev counter for 20 to 30 secs, reconnect battery, switch on ign and push reset button once more. I have my doubts about this in your case but to be sure, it should be done.
If this does not cure fault, the boot liner will have to come out. Being the later type of fuel gauge, as well as the actual fuel sensor in the tank, there will be a TSU (Tank Sender Unit) mounted on the inside of the wheel arch.... item No. 327 in pic below.
Check and clean the connector pins on the TSU and also the connector No.199 on the sensor. Having cleaned them, Full Computer reset again (this should be done each time any of these connectors are disturbed and before each check).
If cleaning has not resolved problem, the sensor will have to be removed from the tank and checked with a meter. With the connections of the sensor upper most (float slides to the bottom... empty tank), the reading across them should be 85 ohms +/- 5, turn sensor upside down (float slides to other end... tank full) reading should be 2.5 ohms +/- 0.5.
If readings are not right, the sensor can be dismantled and visually checked. If you find the sensor is OK, then the TSU (327) will have to be investigated.
See how you go with the above before checking the TSU.
Hope this helps.

John

Thanks for the guidance John. I wasn't expecting a quick fix, but I will follow your instructions when I get the chance, just seem to have 'too many irons in the fire' at the moment!

Paul

Paul check float wire has not snapped?
Note this is inside fuel tank, within sender unit.
I soldered mine back together.

Dave

Thanks Dave, I'll check this out when I go through John's checklist.

Paul

Paul check float wire has not snapped?
Note this is inside fuel tank, within sender unit.
I soldered mine back together.

Dave

Thanks Dave, I'll check this out when I go through John's checklist.

Paul

Paul.... I don't wish to dampen Dave's enthusiasm, all suggestions are always very welcome, but his reference to the float wire (spiral) breaking off and having to be resoldered, refers to the earlier sensor type pre 1990. It is a common fault with that particular sensor ..... Sorry Dave.

Paul check float wire has not snapped?
Note this is inside fuel tank, within sender unit.
I soldered mine back together.

Dave

Thanks Dave, I'll check this out when I go through John's checklist.

Paul

Paul.... I don't wish to dampen Dave's enthusiasm, all suggestions are always very welcome, but his reference to the float wire (spiral) breaking off and having to be resoldered, refers to the earlier sensor type pre 1990. It is a common fault with that particular sensor ..... Sorry Dave.

I understand John. Anyway, I tried the first stage today (resetting etc) and thought I was getting nowhere when I discovered that disconnecting the battery, reconnecting and resetting the trip computer with minimal delay seemed to work (well for now anyway). I have had an indicated 6.7 gallons each time I have switched the ignition on today (and no low fuel light/service warning). Of course there might well be a connection problem somewhere, so will go through the rest of your 'checklist' in due course. Most of the time though my battery is disconnected as the car is used infrequently, so every time we use the car I have to reset the trip computer - can't see why this should matter but perhaps it doesn't help? I'll let you know if I discover any obvious fault. Cheers. Paul.

Anyway, I tried the first stage today (resetting etc) and thought I was getting nowhere when I discovered that disconnecting the battery, reconnecting and resetting the trip computer with minimal delay seemed to work (well for now anyway). I have had an indicated 6.7 gallons each time I have switched the ignition on today (and no low fuel light/service warning).

Paul.... just to clarify, did you do the "full computer reset" first ... ie:- keeping the reset button pressed for 30 secs or so with the battery disconnected ?
John

Anyway, I tried the first stage today (resetting etc) and thought I was getting nowhere when I discovered that disconnecting the battery, reconnecting and resetting the trip computer with minimal delay seemed to work (well for now anyway). I have had an indicated 6.7 gallons each time I have switched the ignition on today (and no low fuel light/service warning).

Paul.... just to clarify, did you do the "full computer reset" first ... ie:- keeping the reset button pressed for 30 secs or so with the battery disconnected ?
John

Yes, did that. Haven't disconnected the battery for a few days now and pressing the reset button doesn't alter the current readout. In that time though I haven't taken the car out, so driving it might well see a 'relapse' as things jiggle about! Paul.

Thanks for the feed back Paul. What would be interesting now would be to disconnect the battery for, say, 24 hrs, reconnect, push reset button once, and see if the fuel reading is still 6.7 gals. There is, actually, a very slim possibility that the "Full" reset has neutralised a "glitch" that could have been lurking around in the computer, but as you say, the acid test is out on the road as your original quote mentioned a certain amount of intermittency with the fault.
Let us know how you get on,
John