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MG Midget and Sprite Technical - Fuel and temp gauge issues, coincidence?

Hi all,

I have just got the midget back on the road after a winter of fettling and storage.

I posted a little while ago about my temp gauge not climbing as it should (coolant definitely gets to temp). It stops about half way.

I fuelled up yesterday to find that the fuel gauge also will lot increase past​ 1/4 even though the tank was brimmed.

I am not thinking there must be a common element.. I have checked and cleaned all earth's and they all have good continuity. Is there some kind of voltage stabilisation or something that would effect them both?

Cheers!
Karl
Karl Bielby

I think there is a voltage stabiliser attached to the bulkhead behind the dash. Maybe that? You can buy modern electronic versions that may give a more stable output.
Jonathan Severn

Hmm is there any other way to test it or diagnose it further?
Karl Bielby

I bought a new stablizer from moss a couple of years ago, and the testing was rather involved ...try going to the moss web site and look up there technical site...im sure they have the instructions on there

Also call mini spares they have a sub section that deals with midgets, they have a great staff if there anything like mini mania here in the usa and will gladly talk to you ...???

At least mini mania tech department has always talked to me...haha

Like you my fuel gauge wont work and my trun signals dont work...but i havent traced down all my grounds and bullets to get a better handle on the problem

1 Paper

Could the float in the tank be stuck? Had that happen to my Midget after a long storage. Had to replace the sending unit itself.

Clare
Clare Ravenwood

It could well be Clare, that was one thing I was going to look at and try to move.

Yeah I did see someone else talking about this technical section of moss' website. Moss USA I guess though? I'll have a look !ater.
Karl Bielby

Karl,
have a look at Paul Hunt's excellent mgb-stuff sites as much applies to Spridgets too.

The VI section covers info about the unit and the importance of earthing the unit and having it fitted the right way up plus a way to test if it's working, see here -
http://www.mgb-stuff.org.uk/electricstext1.htm#stabiliser

Similar sections for fuel sender and gauges.
Nigel Atkins

Prop, try the obvious. Change the flasher in your glove box. They do fail from time to time. That will stop your signals from working.

As for your fuel gauge, run a separate piece of wire from the sending unit to the gauge. That will eliminate any problems on that side of the circuit. The fuel gauge circuits are pretty basic.

Figure out when it worked and what you have done in between when it stopped working. Look at what you had done and see if you can see anything amiss.

Clare

Clare Ravenwood

Tbanks clair,

The problem was it sat to long a year ago... the flasher is fine just deeper issue im cerian its a poor ground ...just no ambition to fix it

Prop
1 Paper

Cheers Nigel I'll have a look at that link.

Yeah that's not a bad idea Clare. Might have a go after looking at Nigel's link.
Karl Bielby

Karl IIRC the stabiliser/regulator is mounted on the back of the speedo in later models, should put out 10 Volts??? If Im wrong someone will pop up soon to correct me.
Cheers
Rod
R W Bowers

In my case the fuel gauge stopped working as did the reversing lights. . . I changed the stabiliser and the problem remained, so its in to the loom for me as and when.
P Bentley

Karl
The fact you have a reading suggests the sender is working. Your car has, I think, an electrical temperature gauge which will be powered via the voltage stabilizer (as well as the fuel gauge). My money is on that. You could try extracting the fuel (or temp) gauge and momentarily applying 12v to the supply terminal. If you get a high reading, replace the stabilizer. The modern electronic one is better anyway.
Bill
W Bretherton

Rod, you might be on to something....

I have had the speedometer out for a refurb, and I could well have wired that thing on the back of the Speedo up wrong... However I don't remember there being too much to get wrong!?
Karl Bielby

Karl, the modern electronic one is a standard three terminal regulator, it will require some wiring to fit. They are readily available from electronic component suppliers in a range of voltages and current ratings. This is the original:
http://www.moss-europe.co.uk/voltage-stabiliser-148876a.html?assoc=511112
This looks to be of modern manufacture and will have a three terminal regulator inside the can. If you want to save 10 quid buy the regulator and wire it up yourself - One earth wire, one 12volt supply and two regulated outputs to the fuel and temp gauges. this is the link to an aussie site, I'm sure you can get one at the local electronics shop.
https://www.x-on.com.au/MPN/BAJ0CC0T?gclid=CIbO9JubxNQCFZkDKgodRs8F8A be careful of current ratings this is only a 1 amp device and may struggle, I would use two, one for each gauge.

However, I think it's impossible to wire it up wrongly as the terminals are male and female as you can see.
Bill's suggestion that the fuel gauge may be causing the issue is valid as it may be pulling the voltage down somehow.
Cheers
Rod
R W Bowers

Rod, The original stabilizer (as you probably know) works by interrupting the battery supply repetitively thus producing a square wave which will have an average of 10v DC. For others reading this, the 10v cannot be measured by a normal voltmeter, you'd need an oscilloscope or true average voltmeter. It is possible that Karl's has "slowed down" thus producing a lower output voltage - I don't know what the typical failure mode is.
Bill
W Bretherton

Thanks Bill as long as mine keeps on working I have no ambition to change it for silicon.
However, I suspect that the new ones are based on a three terminal reg. Only one way to find out and I'm not going to spend 12.5 quid to find out.
Cheers
Rod
R W Bowers

For those that like such things see here - http://www.britishv8.org/articles/mgb-voltage-stabilizer.htm

The solid state pre-built modern style stabliser I bought doesn't seem to be around anymore but for those like me that can't be ar*ed to do it themselves or don't want a condescending conversation in an electronics shop see here, for just two examples -
http://www.ebay.co.uk/itm/Solid-state-voltage-stabilizer-instrument-stabiliser-output-10v-6v-5v-/132212318043?hash=item1ec877df5b:g:1tIAAOSwhvFZCNBE

http://www.ebay.co.uk/itm/Semiconductor-Voltage-Stabilizer-MG-Midget-MGB-MGC-/282527677152?hash=item41c7f63ae0:g:XxEAAOxyRhBS-o2P

The one I've had for a good number of years is similar (same?) as above and does work well below 0C, I think it might have been Rod that told me it wouldn't be as accurate when the weather is cold and he's right but the difference isn't that bad, or often even noticeable, and my fuel gauge readings were more accurate than my wife's previous modern car.
Nigel Atkins

Nigal id like to add to your point above

On our 5 gallon tanks not to many of us will just pass by a gas station willy nilly if the gas gauge is showing 1/4 tank or less so accuracy is not that exculsive


Prop
1 Paper

I strongly believe this is the issue... I can't quite remember if in have a spare or not.. will raid the parts bin when I get chance. But it seems there isn't really a way for me to test it..?
Karl Bielby

Ok just read your link from mgb stuff Nigel, I think I definitely need to check earthing of it, and how its wired up.
Karl Bielby

Karl, if the earth is bad it will probably just supply the full 12v but check it anyway in case it's a high resistance earth and making the stabiliser behave strangely.

You can test it by referring to a test circuit in the MGB article but you'll need a diode, resistor and capacitor so you can measure true average voltage.

You could try my suggestion in my post at 16.27 on 16th June which would verify that the stabiliser output is low. If the stabiliser has an adjustment screw, you could try turning it SLIGHTLY to see what happens.
Bill
W Bretherton

Karl,
Bill's suggestion is good and easy so well worth a go if you can.

In case you missed the link have a look at this for background info and illustration, especially the photo of fuel gauge faces -

http://www.mgb-stuff.org.uk/ivs.htm#
Nigel Atkins

Prop,
there are parts of the UK where you need to fill up when you can as open petrol stations are at times few and far between. On club weekend tours sometimes I've needed to top up or fill up a couple of times on and at the end of a run to save being caught out later.

As it's very hot here at the moment I can't do my usual overfill of the tank, my tank is possibly the 5.83 imperial gallons (7 US gallons) and not the 7 imperial gallons (8.4 US gal) I thought it would be when I bought the car.

I've got a verbal alarm system that cuts in at tank half full and becomes very insistent at quarter full, I've often thought about moving the gauge away from the passenger's side. To be fair in the past I have run out of fuel, even in my present Midget.
Nigel Atkins

Cheers for the links and info chaos.


Got to have a go yesterday. Checked all earth's, checked it's orientation, all was well. So I rooted in the parts bin and found an old one. Put that on and all worked perfectly!

I can only assume the new one I got when my gauge was refurbed is duff or a different type that's not compatible!?

Odd but both gauges are working perfectly now! I knew it couldn't have been sensors or gauges!

Cheers all!
Karl Bielby

Karl,
good to hear things are working again.

Sorry I (and we) didn't know or forgot the IVS was a new one otherwise that would have been the obvious suspect, it was the reason I went electronic years back because the new made original style ones were crap. Same with the new made indicator flasher units, I was given an old s/h original instead and that worked fine.

If you open up the new IVS you may find it's like the new flasher units basically a bit of tin foil inside.

Funny thing as I was wondering if the new made traditional style IVS were any better made now, obviously probably not, when I put up links to the solid state ones.

Unless things have changed there are a few (many?) modern made parts to avoid, there's a thread in the Archive, so don’t assume because a part or component is new it must work.

Also best not to assume the part or component fitted to your car is/was the original or correct type or that it is fitted or working correctly, check and cross reference the information you have – and do the same when ordering parts or components check and cross reference the information, lot of info here too.

Nigel Atkins

To be totally honest, I didn't know it was a new one either.. I have had about 4 gauges in and out a d related bits have all been mixed up a bit after sending and stuff so I wasn't entirely sure what was fitted. I think I might open this new one up and use the link posted above to make my own solid state electronic one. At least I should have a reliable back up then..
Karl Bielby

If you do that put up a photo please of the existing innards of the faulty IVS to see if it's of the new type and what it consists of just for interest and future reference.
Nigel Atkins

Ok I will try and remember when I get round to it.
Karl Bielby

This thread was discussed between 13/06/2017 and 20/06/2017

MG Midget and Sprite Technical index

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