Fuel gauge Sender
Fuel gauge Sender
Author
Discussion

dicktheleg

Original Poster:

30 posts

192 months

Sunday 30th May 2010
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Is this fairly straight forward to remove in a 1999 Chimaera - If I need new gaskets where are they available from - I want to have a go at calibrating the sender a bit better at is currently stays on full for ages them runs out of fiel when gauge still says 1/4 full - I reckon a bit of float arm bending is in order.
Has anyone done this and achieved decent results?
Cheers
Rich

Chimpaholic

9,637 posts

196 months

Monday 31st May 2010
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That's funny, I just did this yesterday!

In my case it was prompted by the following conditions with my fuel gauge readings.

1) Fuel gauge failed to register a full tank even when brimming the tank

2) Fuel gauge indicated the first half of the tank is consumed in 75 miles & the second half in 120 miles

3) Fuel gauge showed empty and the needle fell no further when there is still three gallons left

The sender is very easy to extract, just remove the carpeted panel above the tank and the carpet over the top of the tank itself.

The sender mounting is located on the right hand side of the tank top diametrically opposite to the filler neck.

Just remove the philips head screws and ease the sender wand out at an angle.

When I got my sender on the bench I noticed that the two tabs on the potentiometer that act as the full & empty stops were not allowing the wand to travel though the full range.

I simply tweaked these stop tabs to allow the system to travel the full range of the potentiometer windings.

I also carefully bent the commutator finger (very slightly) that runs against the potentiometer windings to give it a bit more pre-load.

You can access the mechanism by bending back the three tabs that hold the two halves of the potentiometer box together.

BE VERY CAREFUL WHEN YOU GET INSIDE THE POTENTIOMETER BOX, THE WINDINGS ARE EXTREMELY DELICATE.

At this point I decided bending the wand arm was likely to be unnecessary, so I closed up the potentiometer box & put the sender back in the tank.

It goes without saying that you should make sure it goes back in the way it comes out, make a mental note of the connector angle when disconnecting the wiring.

I then went to the fuel station for a fill-up.

The results so far with just over half a tank used are:

1) For the first time brimming the tank showed 100% full on the gauge smile

2) 105 miles travelled when the gauge registered half the tank was used smile

3) Pre-loading the commutator finger has helped reduce the variable gauge readings when cornering, braking & accelerating

In summary, although my tests are incomplete as I have only used just over half a tank I have effected some good improvements.

I am keen to see what happens when I get near the bottom of the tank.

My guess is that now the commutator can run the full range of the potentiometer windings the gauge will keep falling as the fuel drops.

Before my mods the needle stopped moving at the first part of the empty marks, yet I know there was still 60 - 70 miles of fuel left in the tank.

When the ignition is turned off the gauge needle now falls well past the empty marks.

Clearly the full & empty stop tabs on the outer corners of the potentiometer box were not allowing the commutator finger to travel the full range of the potentiometer windings.

The whole job took just 30 minutes from start to finish, well worth doing in my opinion.

Hope this helps?



Edited by Chimpaholic on Monday 31st May 10:43

dicktheleg

Original Poster:

30 posts

192 months

Monday 31st May 2010
quotequote all
That's a superb writ up - thanks for the time and effort to reply to my question.

I'll be doing mine today now and will let you know the outcome, I remember when I built me Westfield I calibrated the sender before fitting it - quite easy to do once it's out of the tank as you can hold it in position and check that the float stops at the top and bottom of the tank, bending the arm end end stops to suit.

Many thanks

Rich

Chimpaholic

9,637 posts

196 months

Monday 31st May 2010
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Good luck Rich, & thanks for your comments.

I am very encouraged by my mods so far.

After what I found I'm inclined to believe the fuel gauge and sender are actually fairly well matched.

Like most things TVR it just needs a bit of careful thought and some adjustment to get it working as it should.

Do let me know how you get on, I will also update this post as soon as I see what happens when my fuel runs low.

It sounds like you have experience with this job but I would definitely try tweaking the full & empty stop tabs on the potentiometer box first before you bend the wand.

I had to move these tabs quite a bit before I was happy the full range of the potentiometer was effective.

When you get the sender mechanism out you will see the tabs stop the commutator finger from travelling the full range of the potentiometer windings at both the upper and lower ranges of resistance (empty & full).

If you do end up bending the wand I would be tempted to introduce a totally new bend on the long straight run.

Tweaking the wand at the bend that's already formed in the wand makes it difficult to return to the original settings if you need to get back to square one.

Putting a new bend in allows you to return the wand to its original setting by simply straightening it back to parallel.

Before my tweaks I never really trusted what the gauge was telling me, preferring instead to re-set my trip at fill-ups and filling up again at a maximum of 230 miles to be on the safe side.

Early indications are that my 30 minute tweak has eliminated my fuel level uncertainty.

Removing the "Am I going to run out" anxieties lets me focus more on the driving pleasures.

I suggest anyone with similarly inaccurate fuel gauge readings spends half an hour to get the full range of the potentiometer windings.

Definitely well worth it.

Dave.






dicktheleg

Original Poster:

30 posts

192 months

Monday 31st May 2010
quotequote all
Thanks again Dave.

I've tweaked my sender as per your instructions, I only needed to tweak the lower limit stop and that proved quite tricky as a minute adjustment had a big effect on the gauge. I did also slightly bend the float arm just because it was bottoming out on the tank before being able to touch the lower limit stop and indicate empty. The one big thing I found was that the fload ball was fitted facing towards the front of the vehicle - as the tank back is sloping it meant that the float fouled the tank wall about half way down the tank - hence it never read below half empty.

I've tested it all and with approx 2" of fuel in the tank it now reads empty thus giving me a small reserve when the needle indicates "E" so I'm happy with that too.

As you said 30 minutes well invested - presumably 30 minutes that the factory could not be bothered to spend when the car was assembled.

I've also fitted uprated headlamp bulbs which is a right faf as the self tappers on the aperature cover were corroded - thanks heavens for Dremmel !!

Almost ready for the Le Mans Classic now - I'll still be carrying a gallon of petrol with me though - Just in case...

Best regards
Rich

Chimpaholic

9,637 posts

196 months

Monday 31st May 2010
quotequote all
Brilliant Rich, interesting discovery with the float too.

I will look at what happens to my gauge when my fuel gets low.

I expect I may need to make some tweaks to the wand too to get it perfect, so your findings are very useful.

Who would have thought it? Between us we have found a couple of tricks to make a TVR fuel gauge semi accurate!

A mutual pat on the back is due me thinks wink

Best regards, Dave.

Yellowsharkkk

4 posts

60 months

Monday 6th June 2022
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Found this really helpful thread even after 11 years lol.
Had problems with my fuel gauge too. Reading empty if the tank was full. Eventually after a few miles it started to swing from empty to full, settling down just above 3/4. More recently had the tank showing just under a 1/4. But found it was empty after running the engine for five minutes. Luckily was at home at the time.
So got the sender unit out. Opened the little box. Watch out for the spring! And moving the arm between the two stops could see when full it wasn’t even touching the wires. Had gone way past. For empty position it wasn’t right at the end of the wires. All I did then was to carefully bend the stops so the small finger ran the full width of the wires. It was very subtle touch to make the difference.
The wires also looked like they had different amount of pressure across them so gentle flex of the finger and spring was done as well. All back together. Making the float had free movement. Took about 30 mins to do.
Just filled the tank up and the gauge is solid on full now for the first time. I’ll see how it goes as the fuel drops. Spare can of petrol in the car just in case!
Pics shoe the wear on the wire and the stops. The pic with the grey background is after adjusting the stops.

Yellowsharkkk

4 posts

60 months

Monday 6th June 2022
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Sorry only seem to be able to do one pic at a time
Here’s side view before making adjustments


Yellowsharkkk

4 posts

60 months

Monday 6th June 2022
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Final adjustment to the stops. Very subtle differences but made a big difference.


bobfather

11,194 posts

272 months

Monday 6th June 2022
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I would worry about adding load to the wiper, the load should be as little as possible to avoid eroding the wound wire resistor

Yellowsharkkk

4 posts

60 months

Wednesday 8th June 2022
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Yes was only slight pressure. Not sure if it did anything really. It didn’t look different. Just stretching out the spring slightly was good enough to do it