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5th January 2021, 17:15 | #21 | |
This is my second home
R75 Saloon. Join Date: Feb 2009
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5th January 2021, 17:47 | #22 |
Posted a thing or two
75 Conn CDT Tourer, 75 Conn SE V6, 75 Conn V6, 75 Conn CDTi Tourer, ZS 180 Join Date: Jan 2014
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Sorry.....there you go, have two
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5th January 2021, 19:14 | #23 | |
Doesn't do things by halves
Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007
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Simon PS It's not "on board" diagnostics, that's the system that uses the socket under the steering wheel. It's the separate instrument pack diagnostics. Everyone gets it wrong!
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5th January 2021, 21:43 | #24 | |||
This is my second home
Rover75 and Mreg Corsa. Join Date: Nov 2006
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TC |
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5th January 2021, 22:10 | #25 | |
This is my second home
Rover 75 tourer Club CD/Limo Tints Join Date: Nov 2008
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Number 6
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5th January 2021, 23:46 | #26 | |
Posted a thing or two
75 Conn CDT Tourer, 75 Conn SE V6, 75 Conn V6, 75 Conn CDTi Tourer, ZS 180 Join Date: Jan 2014
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PS - parked in work tonight on completely level ground, gauge showing 3/8ths of a tank when I switched off. Came out later, switched on the ignition and the needle immediately shot up to 3/4 - odd in itself. But then after a few seconds it slowly climbed up to full, stayed there for a few seconds, then gradually dropped back to 3/4 again ??? I'm beginning to think there's a ghost in the tank, playing with the sender arms....
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6th January 2021, 07:31 | #27 | |
This is my second home
Rover 75 tourer Club CD/Limo Tints Join Date: Nov 2008
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Well thats scuppered that then as I dont have Rave Will just have to zero the tripometer every time I fill it up and every 400 miles top it up again.
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6th January 2021, 08:17 | #28 | ||
Doesn't do things by halves
Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007
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I'd try test 21 if I were you. Simon
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6th January 2021, 18:23 | #29 |
Posted a thing or two
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Tried the software reset first thing today, but it hasn't solved the issue on my car unfortunately - an hour or so later the needle was going up & down all by itself again whilst parked with the ignition on.
So spent a few hours playing with some known value resistors (that all fall within the normal range of the senders in series), to see if I could get the gauge to show what I was expecting. Having measured the resistance of an old spare set of pump & filter units on the bench, I confirmed the upper and lower values. Interestingly, the O/S and N/S circuit boards are actually slightly different in appearance and gave different upper values. Drivers (pump) O/S: 5 to 165 ohms Passenger (filter) N/S: 5 to 195 ohms Both units have the lowest resistance (5 ohms) when the float is at the bottom i.e. low fuel level. I also checked the resistances at varying points along the track, and again confirmed that the values are pretty much exactly linear (which makes life much easier.... ) Armed with this info, you can calculate that the gauge should show a full tank when it 'sees' approx 350 ohms, a completely empty tank at 10 ohms, half a tank at about 175 ohms and so on. So equipped with the following resistors, I disconnected the plug on top of the pump, inserted each resistor into the wires that go to the dash, then switched on the ignition to see if I could fool the gauge into giving the expected reading. (Approx values due to 10% resistor tolerences): 41 ohms (act. 48) - 1/8 of a tank 82 ohms (act. 89) - 1/4 of a tank 150 ohms (act. 174) - 1/2 a tank 270 ohms (act. 297) - 3/4 of a tank 330 ohms (act. 362) - full tank Each resistor produced exactly the expected reading on the fuel gauge, and having tested the varying values a total of maybe 20 times, in different orders, there was no sign of any unusual behaviour of the gauge needle. So my thoughts are moving towards the sender units, or connection on top, but will investigate further next week once I've made up a temporary link lead to run the in-tank fuel pump with the senders disconnected - I'll insert a resistor and see how the gauge behaves over a few days and under varying parked and driving conditions. Will report back with my findings in due course, but have already bought two new tank seals in anticipation of 'going internal'.... PS - they are the same seal as used on a Discovery 2
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11th January 2021, 23:27 | #30 |
Posted a thing or two
75 Conn CDT Tourer, 75 Conn SE V6, 75 Conn V6, 75 Conn CDTi Tourer, ZS 180 Join Date: Jan 2014
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Quick update on this one - managed to spend a few more hours on it today, and made up the temporary link-lead to allow power to be supplied to the in-tank fuel pump, whilst leaving the sender units disconnected.
This meant that I could now run the engine, whilst substituting known value resistors in the place of the senders, by carefully inserting them into the end of loom connector. Contrary to other posts in this thread regarding possible algorithms and the fuel gauge remaining fixed whilst filling up, I can now confirm the gauge does in fact move both up and down with the engine running or with just the ignition on, if the resistance is varied. Once again, having obtained the anticipated results at the gauge with the car's tank senders removed from the circuit, it's looking very likely that the fault lies with one or both rheostats. However, I'll test it for a few days with resistors in place, just to confirm the eratic needle behaviour has stopped, before having a look inside the tank.
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