Diesel fuel gauge erratic/fauly?

[grivas]

Today I went for a drive with my wife and I was aware that I had a little over a quarter of a tank full of diesel as indicated by the gauge, but about a couple of miles of travel and I noticed the low fuel warning light come on and the gauge needle had dropped to less than an 1/8th or less full indicated, as I was near an Esso station I decided to fuel up, so I stopped and put in 20 litres where upon the gauge needle moved to 3/4 full. On our way back home, approx. 35 miles later I stopped at Sainsbury's for some shopping and decided to top up the fuel, but I was only able to put in a further 16 liters approx. before the tank was brimmed, what I don't understand is if the tank has a 65 litre capacity, the warning light should not have come on when it did as I would have had at least 30 litres in the tank at the time the warning light illuminated, at least that is what I estimate.
What is happening?, I do know the gauge in these cars is stupidly inaccurate?, any ideas?.

[Robson Rover Repair]

Probably find the sender has jammed on one side. Or if you had an intank pump recently done it was twisted then.

I once owned a 75 owned by a ham fister owner who had changed the intank pump so badly, that when you put in as little as 5 litres from the red light being on the car was convinced you where almost full.

I must admit I drop it for a few years and after running out a few times I eventually ripped the whole lot out, tank and all, and did a full replacement of everything properly to get it right.

12 years later the cars still on the road in Basingstoke now.

[grivas]

Thanks for the reply, I haven't had a new pump fitted and I can't understand how the sender could have got stuck, can it be unstuck without taking the whole thing apart?

[grivas]

I have just taken some readings using the diagnostics tool and these are :
--6.0 --0570
--6.1 -----
1-6.2 --0570

Now I am not sure how to interpret these , but it appears that one of the sensors might be malfunctioning?, so if anyone has any ideas please explain. Thanks

[grivas]

I also understand that there was some discussion regarding a 'software reset' within the diagnostics package which in at least one case has been successful in curing the erratic behaviour of the fuel gauge.
Does anyone have any recent experience with this or any other information, I understand that member T-cut has some knowledge and/or experience in this?.
Please help if possible, thanks.

[grivas]

Final plea for any useful information on this subject, all the search carried out leads to either inconclusive solutions, or solutions where no detailed information is offered by people who managed to successfully solve the issue, missing photos make matters worse.
Anyway thanks to those who have taken the time to offer some suggestions.

[SD1too]

Hello Mac,

The fuel gauge is normally reliable and accurate since the instrument pack algorithm takes into account the rate of fuel consumption as well as the level readings. However I've read of a few owners who have experienced the same symptoms as you have described and it's always on a diesel.

One member investigated this comprehensively and found that the tank rheostat had worn away over a section of its travel. I suspect that this might happen due to the miserly fuel consumption of the diesel, coupled with topping-up the tank with a small amount of fuel such that the gauge is always reading in about the same place. This is just my theory, I have no proof but if you recognise this as something that you do, it might be the explanation.

Regarding the 0570 display which you obtained from the instrument pack diagnostics, you can find T-Cut's article on this in the "How to" section of the forum. I think it probably means that you have 57.0 litres of diesel in the tank. The IPK cannot distinguish between left and right senders since they are wired in series at the tank connector.

Simon

[grivas]

Originally Posted by SD1too

Hello Mac,

The fuel gauge is normally reliable and accurate since the instrument pack algorithm takes into account the rate of fuel consumption as well as the level readings. However I've read of a few owners who have experienced the same symptoms as you have described and it's always on a diesel.

One member investigated this comprehensively and found that the tank rheostat had worn away over a section of its travel. I suspect that this might happen due to the miserly fuel consumption of the diesel, coupled with topping-up the tank with a small amount of fuel such that the gauge is always reading in about the same place. This is just my theory, I have no proof but if you recognise this as something that you do, it might be the explanation.

Regarding the 0570 display which you obtained from the instrument pack diagnostics, you can find T-Cut's article on this in the "How to" section of the forum. I think it probably means that you have 57.0 litres of diesel in the tank. The IPK cannot distinguish between left and right senders since they are wired in series at the tank connector.

Simon

Hi SD1, thank you for the reply and very valuable information. Regarding the fueling, I normally top up 30 or 40 litres of fuel when the gauge is at 1/4 full as I don't do much driving now, regarding the 0570 figure,it it quite possible that the tank is nearly full ( theoretical max being 65 litres),according to the example T-Cut gives in the diagnostics write-up he quotes six figures something like 109330, that is 10.9L in the left side and 33.0L in the right side of the tank,total being the sum of the two, so not sure what is going on.
The gauge rises to the very top when the engine is turned on,and fall to the bottom when turned off.

[SD1too]

Hello Mac, thanks for coming back to me. Based on the further detail you've given I can shed some more light on this.

Originally Posted by grivas

... I normally top up 30 or 40 litres of fuel when the gauge is at 1/4 full ... The gauge rises to the very top when the engine is turned on ...

It's important to bear in mind that if my theory is correct, the indications on your gauge will not necessarily be accurate and so should not be relied upon.

Originally Posted by grivas

... according to the example T-Cut gives in the diagnostics write-up he quotes six figures something like 109330 ...

Directly below that T-Cut has added "EDIT 7 October 2019" in which he says: "I think the instructions for Section 6 are wrong" and explains the true interpretation. As I've pointed out, it is impossible for the IPK to give separate capacities for the left and right sections of the tank so the initial 6.0 explanation is definitely wrong!

Originally Posted by grivas

... so not sure what is going on.

The readings you've given in post no. 4 are consistent with those my car shows.

• Test 6.0 shows the total fuel volume, 0570 being 57.0 litres.
• Test 6.1 is not functional on the 75/ZT.
• Test 6.2 is untrustworthy since it would be extremely complicated for the IPK to detect a faulty tank sender as they are wired in series.

Mac; my suggestion is that you fill your tank to the brim, determined using the cut-out on the pump. Reset your trip mileometer to zero. Drive your car, monitoring the gauge needle for abnormal movement until it indicates nearly empty. Refill the tank to the brim as before, noting the quantity of diesel purchased and the mileage covered. Calculate the mpg and observe whether the figure is valid. That should tell you whether or not you have a fault. If you do, it will most likely be rheostat wear as discovered by the member already mentioned. You have said that you refill with about the same quantity when the gauge reaches 1/4 which supports a worn rheostat since the wiper will always be traversing the same section. In that event, the reliable solution is replacement.

Simon

[grivas]

Originally Posted by SD1too

Hello Mac, thanks for coming back to me. Based on the further detail you've given I can shed some more light on this.

It's important to bear in mind that if my theory is correct, the indications on your gauge will not necessarily be accurate and so should not be relied upon.

Directly below that T-Cut has added "EDIT 7 October 2019" in which he says: "I think the instructions for Section 6 are wrong" and explains the true interpretation. As I've pointed out, it is impossible for the IPK to give separate capacities for the left and right sections of the tank so the initial 6.0 explanation is definitely wrong!

The readings you've given in post no. 4 are consistent with those my car shows.

• Test 6.0 shows the total fuel volume, 0570 being 57.0 litres.
• Test 6.1 is not functional on the 75/ZT.
• Test 6.2 is untrustworthy since it would be extremely complicated for the IPK to detect a faulty tank sender as they are wired in series.

Mac; my suggestion is that you fill your tank to the brim, determined using the cut-out on the pump. Reset your trip mileometer to zero. Drive your car, monitoring the gauge needle for abnormal movement until it indicates nearly empty. Refill the tank to the brim as before, noting the quantity of diesel purchased and the mileage covered. Calculate the mpg and observe whether the figure is valid. That should tell you whether or not you have a fault. If you do, it will most likely be rheostat wear as discovered by the member already mentioned. You have said that you refill with about the same quantity when the gauge reaches 1/4 which supports a worn rheostat since the wiper will always be traversing the same section. In that event, the reliable solution is replacement.

Simon

Thank you Simon, you have given me very helpful information here and will certainly carry out the brim to brim test to check mileage, also the information on the functioning of test 6.0 sheds a new light on things. At the moment the tank is brimmed and the gauge is at the max setting to the top, when the ignition is in position 2, dropping to zero or empty when off, the diagnostic indicates 57 litres not far off 65 litres which is the max, so will report back when I have the results,it may be a while, thanks again.