 | Home > Technical > Request for a second opinion on Fuel Gauge |
 
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6632   
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Is it stuck on full deflection or does it start off above full then drop as normal?
The Puma instrument pack isn't like a traditional moving needle gauge where less resistance -> more current -> more deflection. The sender resistance is measured as a voltage drop by the instrument pack microprocessor which does the damping (and error checking) and moves the needle and turns on the warning lamp when needed. It also sends the fuel level out as a CAN bus message for the engine ECU to use. So, if you see what I mean, the needle isn't directly connected to the sender. There also isn't a wheelarch connector to unplug to check this. The only inline connectors in the fuel sensor circuit is the pair mounted on the top of the driver's footwell - a 14 way grey connectors alongside a 1 way and 4 way. The correct replacement in-tank pickup/sender part for a 2.4 90 is WQB100430. There's no pump on it, the extra bit you're not expecting to see is the fuel swirl pot. You could remove the instrument pack connector and do a resistance test of the sender as it stands now.  1988 90 Td5 NAS soft top
2015 D90 XS SW |
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23rd Sep 2019 9:07pm |
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| Martin Site Admin Member Since: 02 Apr 2007 Location: Hook Norton Posts: 6632
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Click image to enlarge C0376 and the matching C0390 (on a 90) are the 14 way ones mentioned above  1988 90 Td5 NAS soft top
2015 D90 XS SW |
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23rd Sep 2019 9:10pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17537 
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My 07 Puma gauge was originally very non-linear and would be well off the scale if the tank was full, remaining that way for around the first 100 miles (actually about 1/4 of a tank). It would then drop at an accelerating rate, so the last 1/4 of the tank accounted for about half the FSD (full scale deflection) of the gauge.
I changed the sender a year or so ago after the original split (for a new genuine part) and the new one was perfectly linear. It's still well of the scale when full, but now drops evenly as the fuel is consumed. The replacement sender for the Puma, which is essentially the same as a TD5 but without the pump, was shockingly expensive and was about the same as a TD5 unit complete with pump, another depressing example of LR's absolute rip-off pricing. The part number you quote (WQB100440) is as far as I know the correct one, but it doesn't help that firms that should know better, such as LRDirect, describe it as "In tank fuel pump & sender..." when it does not include a pump! I almost wonder whether the description was carried over from the TD5 accidentally, and the price was also carried over accidentally. I haven't tested it, but generally fuel gauges go to FSD if they are open circuit, so it is possible that you have a faulty connection or broken wire. Unfortunately the sender is completely inaccessible unless you drop the tank, and even accessing the connectors on the unit require the tank to be lowered. It is not a pleasant job. |
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23rd Sep 2019 9:29pm |
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| llessur Member Since: 15 Nov 2011 Location: Hereford Posts: 151
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Thank you all
I will start with a resistance check at the instrument pack connector. (The full deflection is only after the ignition is turned on) I will let you know how I go, but if it means dropping the tank I will probably look at changing the hoses and sender at the same time. |
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24th Sep 2019 6:34am |
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