Repairing the low fuel warning light. - Page 3

PPuxley · 20-09-2021, 12:42 PM

Quote:

Originally Posted by Luddite

I think the OE thermistor-based sensor takes around 30-40 seconds of exposure before it triggers the light so maybe try, say, 20 seconds to accommodate any 'sloshing' and work from there.

Thanks. Yes, when I tested one it took at least that.
Really, the longer the better, within reason, a couple of minutes even isnt going to use significant amounts of fuel that you'd be left stranded, and it would put it beyond doubt for false triggering.

PPuxley · 22-09-2021, 04:34 PM

Confirmation that the conversion works on an i.e. model sender.
Working prototype. A finished version would have a shorter and neater sheathing to the module.
Thanks to Davey (Rostrumorhospit) for the donor.

hh93 · 22-09-2021, 05:12 PM

Patrick - the "just replace the Thermistor" is a viable repair though ? I haven't missed anything to say it isn't or have I missed something ?

Since there is no reserve switch, a reliable Low Fuel Light is a real need on Doris. I'd rather not pay for a OEM part when I need one.

PPuxley · 22-09-2021, 05:16 PM

Quote:

Originally Posted by hh93

Patrick - the "just replace the Thermistor" is a viable repair though ? I haven't missed anything to say it isn't or have I missed something ?

Since there is no reserve switch, a reliable Low Fuel Light is a real need on Doris. I'd rather not pay for a OEM part when I need one.

Probably but Ive never really pursued it

PPuxley · 28-09-2021, 06:20 PM

A bit more messing around on a rainy day and waiting for stuff to arrive to finish off the M900.

I have now developed a much smaller module (based on a 555 timer chip to control the on delay).

This will fit inside the OEM Fuel sender body (plastic type)

The only outward difference to OEM would be an earth tag, otherwise it would plug straight into the OEM loom Superseal connector.

jerry · 28-09-2021, 07:34 PM

You are a very clever chap with electronic bits

PPuxley · 28-09-2021, 07:41 PM

Quote:

Originally Posted by jerry

You are a very clever chap with electronic bits

Theres nothing that Google wont tell you!!

PPuxley · 14-10-2021, 02:34 PM

Update in use
I have been out and about on mine and running at various fuel levels in the tank and the sender is working perfectly when it gets to the critical level it comes on and goes off and on again every 30 seconds and then after 4 or 5 miles remains on permanently.
I haven’t yet tested what the mileage available is after it comes on.

PPuxley · 24-10-2021, 10:43 AM

Another one complete.
VIDEO

PPuxley · 16-11-2021, 10:51 AM

Just an update to say that ive been running the reworked fuel sender for a month or so now. However with a full tank and not much riding I hadnt reduced fuel enough for it to trigger.
Today I drained the tank (needed some mower fuel) and the warning light duly came on.
So its survived a month immersed in fuel

VIDEO

PPuxley · 13-07-2022, 03:32 PM

A bit of a long term update. In short forget any of the solid state repair/replacements discussed above. They work in principle and would have longevity if the metal versions of the sensor were used- problem is the metal sensors are prohibitively expensive and you would be no better off than OEM in terms of cost.
I have now reverted to the standard thermistor approach using these that I can only seem to find from China, for less than a tenner.
https://www.aliexpress.com/item/32872117309.html

I simply remove the old head, drill right through the tube and fix the new one sealing the tube completely with JB weld. Just remember that if you block the drain holes at the base of the thermistor cover you must drill some 2mm holes in the side at the base to allow the fuel to drain as the fuel level lowers.
They work as OEM although they do not light the dash lamp quite as brightly
The one shown below uses an aluminium tube housing I machined to fit the base, but you can easily use the original OEM stem, just remove and replace the top.

22-09-2021, 04:34 PM	#32
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	Confirmation that the conversion works on an i.e. model sender. Working prototype. A finished version would have a shorter and neater sheathing to the module. Thanks to Davey (Rostrumorhospit) for the donor. __________________ Golf-My favourite game. While my wife plays I'm in the workshop.

22-09-2021, 05:12 PM	#33
hh93 Member Join Date: Jul 2018 Location: Lincoln Bike: M620ie Posts: 116	Patrick - the "just replace the Thermistor" is a viable repair though ? I haven't missed anything to say it isn't or have I missed something ? Since there is no reserve switch, a reliable Low Fuel Light is a real need on Doris. I'd rather not pay for a OEM part when I need one. __________________ Doris '03 620 Dark Horace 1980 onwards Harris Mag II

28-09-2021, 06:20 PM	#35
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	A bit more messing around on a rainy day and waiting for stuff to arrive to finish off the M900. I have now developed a much smaller module (based on a 555 timer chip to control the on delay). This will fit inside the OEM Fuel sender body (plastic type) The only outward difference to OEM would be an earth tag, otherwise it would plug straight into the OEM loom Superseal connector. __________________ Golf-My favourite game. While my wife plays I'm in the workshop.

28-09-2021, 07:34 PM	#36
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	You are a very clever chap with electronic bits __________________ MONSTERMAN

14-10-2021, 02:34 PM	#38
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	Update in use I have been out and about on mine and running at various fuel levels in the tank and the sender is working perfectly when it gets to the critical level it comes on and goes off and on again every 30 seconds and then after 4 or 5 miles remains on permanently. I haven’t yet tested what the mileage available is after it comes on. __________________ Golf-My favourite game. While my wife plays I'm in the workshop.

24-10-2021, 10:43 AM	#39
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	Another one complete. VIDEO __________________ Golf-My favourite game. While my wife plays I'm in the workshop.

16-11-2021, 10:51 AM	#40
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	Just an update to say that ive been running the reworked fuel sender for a month or so now. However with a full tank and not much riding I hadnt reduced fuel enough for it to trigger. Today I drained the tank (needed some mower fuel) and the warning light duly came on. So its survived a month immersed in fuel VIDEO __________________ Golf-My favourite game. While my wife plays I'm in the workshop. Last edited by PPuxley; 16-11-2021 at 11:34 AM..

13-07-2022, 03:32 PM	#41
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	A bit of a long term update. In short forget any of the solid state repair/replacements discussed above. They work in principle and would have longevity if the metal versions of the sensor were used- problem is the metal sensors are prohibitively expensive and you would be no better off than OEM in terms of cost. I have now reverted to the standard thermistor approach using these that I can only seem to find from China, for less than a tenner. https://www.aliexpress.com/item/32872117309.html I simply remove the old head, drill right through the tube and fix the new one sealing the tube completely with JB weld. Just remember that if you block the drain holes at the base of the thermistor cover you must drill some 2mm holes in the side at the base to allow the fuel to drain as the fuel level lowers. They work as OEM although they do not light the dash lamp quite as brightly The one shown below uses an aluminium tube housing I machined to fit the base, but you can easily use the original OEM stem, just remove and replace the top. __________________ Golf-My favourite game. While my wife plays I'm in the workshop.