Modified or standard fuel sender unit? Advice please!

Modified or standard fuel sender unit? Advice please!

Author
Discussion

jim290s

Original Poster:

34 posts

120 months

Wednesday 8th April 2015
quotequote all
Hi all,
I've had issues with the fuel gauge reading ever since I bought the car last year, but recently it's been getting worse. Anything less than ~3/4 full and the gauge reads empty. I have checked that connecting the two sender wires shows a 'full' tank gauge, so I'm assuming that the sender is at fault.
I have already searched the forum for tips regarding replacing the sender, but none of the sender units pictures in the threads on this forum match my particular unit...
This thread shows a different sender to mine. I haven't seen any with only the single positive terminal.
It's making me think that perhaps the unit has been replaced by something completely different at some point, or that I haven't seen a picture of the original TVR unit anywhere.

All I would like to know is, if I order the recommended Land Rover Defender sender unit Land Rover Defender sender unit, will this fit the hole in my fuel tank?


See pictures below for details:



For comparison with the thread showing resistance values, my current sender is showing 615 Ohms when the tank is ~3/4 full, so I'm assuming this is faulty as it should be between 20-300 ish (full to empty). Any advice would be appreciated, apart from just leaving it as it is :P
I'd quite like to know how far I can get before running out of petrol this summer!

greymrj

3,316 posts

203 months

Wednesday 8th April 2015
quotequote all
I may be wrong, but do you have one terminal on the sender and the other 'earthed' to the tank? If so, are you absoluetly confident there is a good enough earth between sender and tank? I wouldn't be the least surprised if there wasnt given the way the sender is installed, and especially if there is any corrosion.

At least that problem shouldnt arise if both terminals are on the sender unit. Provided of course you check that the black wire at the sender does actually have continuity with earth. (The feed wire should be black with a grey tracer).

The problem with any alternative sender unit, and there is more than one which will fit into this hole, is to get the length of arm and the position of the float correct so that an empty tank has the contact at the bottom of the arc and the full tank has the contact at the top of the arc. You have little choice but to bend the wire until you achieve that. I think you will find, for example, that the Landrover Defender unit is initially too long and actually hits the first baffle in the tank so it reads the same over about 70% of the tank level.

Car Builder Solutions and Demon Tweeks do a generic unit which will fit the opening, and has two terminals, but you will need to adjust it to match the fuel level range in the tank. I got it reasonably close, and even fitted a small 'paddle' on the wire to act as a damper. Unfortunately the 'generic' unit recently seems to have given up the ghost after less than 2 years.

v8s4me

7,234 posts

218 months

Wednesday 8th April 2015
quotequote all
That's very different to mine and the others I've seen. The diameter of the back plate on mine is 60mm so if your hole is bigger than that the LR one won't fit. In any event I'd suggest buying elsewhere given the experience I had. I wouldn't be too concerned with the difference between the resistance showing on yours compared to mine as what is important is the differential between "full" & "empty". So long at enough power is getting to the gauge to show full at one extreme and empty at the other the increments in between are a bit pot-luck. If you really want to do something other than leave it as it is, then take it out and clean the terminals and check the float hasn't sprung a leak.

After all the trouble I went to mine still lies to me. It reads empty when I still have about 80 miles worth of fuel still in the tank. Anyway, why should you have an accurate fuel gauage? No one else has laugh

jim290s

Original Poster:

34 posts

120 months

Wednesday 8th April 2015
quotequote all
Thanks for the replies. After a bit more of a thorough search, I have found a couple of posts with senders which look like mine here and here

Before buying anything, I'll check the corrosion between the sender unit and tank as you suggested. It could be that the extra ~300 Ohms or so are down to rust etc. Does the fuel tank need earthing anywhere other than the tab shown in my photo, or is there another earth point I should know about/check?
Cheers for the help

v8s4me

7,234 posts

218 months

Wednesday 8th April 2015
quotequote all
jim290s said:
......I'll check the corrosion between the sender unit and tank as you suggested. It could be that the extra ~300 Ohms or so are down to rust etc....
Quite possibly.

jim290s said:
..... Does the fuel tank need earthing anywhere other than the tab shown in my photo, or is there another earth point I should know about/check?..
Unless you know the other end of that earth wire goes to a good clean earth I'd run a new earth wire from the tank to the chassis just to be sure.

v8s4me

7,234 posts

218 months

Monday 20th April 2015
quotequote all
How did you get on?

dwhitaker

174 posts

122 months

Tuesday 21st April 2015
quotequote all
Pop it out and give the wiper a good few squirts of contact cleaner. Mostly likely corrosion / fuel residue on the contacts. Could also be a failed float. Floats are available. At least with it out you can move it the full range and see effect on gauge.

jim290s

Original Poster:

34 posts

120 months

Tuesday 21st April 2015
quotequote all
I've ordered a new landrover defender sender unit and locking ring. If I'm going to go through the hassle of re-sealing the sender anyway, it may as well be a brand new one! This job has now fallen a little down the TVR list as my alternator has now packed in...
Don't want to change the theme of the thread too drastically, but has anyone got advice on where to source a new one.
The one on my car is exactly the same as this but I don't fancy spending £132 unless this is the only option.

AutoAndy

2,265 posts

214 months

Tuesday 21st April 2015
quotequote all
....also, just make sure it is orientated correctly...had one that wasn't and just needed rotating round to read better... wink

phillpot

17,105 posts

182 months

Tuesday 21st April 2015
quotequote all
jim290s said:
has anyone got advice on where to source a new one.
Bit cheaper.



Griffinr

1,017 posts

173 months

Tuesday 21st April 2015
quotequote all
jim290s said:
This job has now fallen a little down the TVR list as my alternator has now packed in...
Don't want to change the theme of the thread too drastically, but has anyone got advice on where to source a new one.
The one on my car is exactly the same as this but I don't fancy spending £132 unless this is the only option.
It would be cheaper to get yours overhauled, or maybe just try a new diode pack. It's just held with 2 screws on the terminal end of the alternator. Mine packed in a few years ago and when I took the diode pack off the brushes had stuck. Freed them up and put it back on and it's been fine since.
Rob.

v8s4me

7,234 posts

218 months

Tuesday 21st April 2015
quotequote all
dwhitaker said:
.... Could also be a failed float. Floats are available. ...
Where from please?

jim290s

Original Poster:

34 posts

120 months

Friday 24th April 2015
quotequote all
Well... after I was told by a garage that I needed a new alternator, and then taking the alternator out and taking it to get reconditioned, I was then told by the re-con chap that the alternator was producing the correct voltage and working fine.

I've re-fitted it into the car and after lots of searching on this forum I think the root cause is a lack of coil activation voltage to the alternator in order to get it started. Got the multimeter out and realised that the bulb has blown for the alternator charging circuit. Wish I'd checked that first now!

Does anyone have a link for a 5w replacement bulb. I'm not that interested in an LED replacement, I just want the easiest fix to swap straight back in there. My car is an F reg S2 if that helps? Also, how to you get the old bulb out? Do you have to remove the plastic fascia over all the instruments and re-glue it from the front, or is there a way to remove the bulb holder from the rear of the dash. I had a go last night but couldn't seen to pull it out from the back. What a faff!

phillpot

17,105 posts

182 months

Friday 24th April 2015
quotequote all
jim290s said:
Well... after I was told by a garage that I needed a new alternator.....
Good garage eh !



jim290s said:
Does anyone have a link for a 5w replacement bulb. I'm not that interested in an LED replacement
Any half decent car accessory shop/motor factor should have a bulb. Don't use LED, it won't draw enough current to "excite" the alternator.

I'd imagine the bulb holder pulls out from behind? ..... but this is a TVR we're talking about wink

Bobhon

1,057 posts

178 months

Friday 24th April 2015
quotequote all
phillpot said:
I'd imagine the bulb holder pulls out from behind? ..... but this is a TVR we're talking about wink
I imagined that too when I took the whole dash out on my S2, but I was wrong. They don't pull out from behind, seem to be glued in permanently.

I never did get to change the bulbs, so hopefully someone who has will post up how to. I now imagine that you have to take the curved cover off, but don't take my word for it.

Bob

jim290s

Original Poster:

34 posts

120 months

Saturday 25th April 2015
quotequote all
So I did eventually manage to get the bulb out today. The red part is still in the dash, but the lamp bit slid out of the back (after a while). Question is, where do I find a replacement which will fit back into the red lamp housing which is still in the dash? Or just a replacement bulb? I can't see any way of removing the red bit in the dash without taking off the front cover-panel, so I'd prefer not to replace the whole unit. The offending article is below. Also, needs to draw 5w in order for my alternator to work again!

phillpot

17,105 posts

182 months

Saturday 25th April 2015
quotequote all
Possibly you'll have to buy the complete warning lamp, most car shops have a rack of all sorts of odds 'n sods in little blister packets, be surprised if they didn't have a "universal" warning lamp.





If you can't find anything locally, something like this would do. Just pop the bulb and holder bit out of the back and put into yours.

jim290s

Original Poster:

34 posts

120 months

Tuesday 28th April 2015
quotequote all
Right, time for a quick update back on the original topic!
Finally got my replacement sender fitted this evening. I ordered this unit from eBay and it came with a new seal and lock ring.

After removing the old sender, I did a trial fitting and found a couple of issues.
1. The replacement is too long to fit in my tank due to baffles which I didn't realise were in there.
2. The plastic base on the new sender is much thinner than the original unit, so the new lock ring, seal, sender combo thickness isn't enough to provide a seal.
3. The replacement has two plastic 'locators' on the rear of the plastic base plate. These didn't fit into the inside diameter of the hole in my tank. Probably only 1mm in it, but I didn't want to crack the plastic by forcing it.

Solutions:
1. Took the float off the old unit (after checking it still floats in fuel) and cut/bent the new sender wire to fit the tank baffles etc.
2. Did a trial fitting using the old rubber seal + new rubber seal on each side of the sender to make a 'sender sandwich' and make up the lost thickness to provide a seal.
3. Filed off one of the two plastic locators on the rear (as they didn't locate into anything on my tank (they probably do on a Landrover to ensure the sender stays vertical during tightening, but not on a TVR...)
If you also take the locators off, you will want to angle the sender by about 45-90 degrees, so that once it's tightened (and turns with the lock ring) it sits vertically in the tank.

Old and new, as delivered:


After revision 1 (still too long to fit) using float from old unit:


After revision 2 (finally fitted):


From the side (as fitted):


I also used some non-setting fuel resistant gasket compound to try and help the seal work.
I'll update once I've been through a full tank of fuel to see how accurate it is now! Hope this is useful for someone. Now to fix the alternator lamp... ordered a 1.5W bulb and a 20 Ohm 4W rated resistor, so hopefully I can trick the alternator into thinking it's 5W.

v8s4me

7,234 posts

218 months

Tuesday 28th April 2015
quotequote all
jim290s said:
..Solutions: 1. Took the float off the old unit (after checking it still floats in fuel)...
Smart move.

If you get a fuel tight seal first time I'd be inclined to leave it at that even if it is still not completely accurate. If you take it out again you might find yourself fiddling messing with it over and over trying to get it to seal again. Drive the thing! thumbup

phillpot

17,105 posts

182 months

Tuesday 28th April 2015
quotequote all
jim290s said:
I also used some non-setting fuel resistant gasket compound to try and help the seal work.
No secrets here, what brand of "super goop" have you used?