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MG Midget and Sprite Technical - Fuel gauge problem

Morning All
On the way home yesterday (roof down of course!) I noticed the fuel gauge was showing a prodigious emptying of the tank. As I'm sure four Olympus engines borrowed from the Vulcan hadn't been installed while I was at my desk, I surmised it must have been an electrical problem.

The tank was about half full (or half empty depending on your point of view)and the needle started drifting towards empty until it was at the stop. A minute or so later it moved upwards to about 1/3 tank, then drifted back to the empty mark, where it stayed.

I've checked behind the dash, all looks ok as far as I can see, no obviously loose wires. I did do some work in that area at the weekend, fitting an accessory socket, taking the feed from a spare tab on the ignition switch, and making a new earth connection, but the gauge was showing no problems until yesterday.

Any ideas please anyone?

Dom
Dominic Excell

Sender wire earthing out somewhere? Disconnect it and see what happens.
Greg H

yeap or poor connection somewhere (possibly earth wire) as it seems to be (or was) an intermittent supply to gauge

not sure if it would be that old fashioned voltage stabiliser or it's connections (I've never been sure if these need fitting upright)

for future use, you should recognise it -

Solid state voltage stabilizer: (on eBay, damned link has stopped working here)


Nigel Atkins

Could also be a punctured float on the sender unit.

Trev
T Mason

There is an article about punctured floats in this month's MASCOT mag. One of the benefits of joining!
G Williams (Graeme)

And our foreign tours
Alan
www.masckent.org
Alan Anstead

Would a punctured float move back up once it had initially sunk? That would be a handy trick to know, especially for the nautically inclined.

My money's on a loose connection or short, since you never read higher than the actual level of the tank.

The voltage stabiliser for the fuel gauge is an interesting piece of engineering. Being bimetallic like the gauge, it corrects for voltage fluctuations and for ambient temperature changes, which is handy in a car with lots of fresh air and not so much of the heating. A solid-state replacement won't correct for ambient temperature changes, but as long as you're aware that your gauge reads lower in winter and higher in summer, you'll be ok. If you're curious, Google "lucas bimetal voltage stabiliser" for some neat articles and lots of lovely pictures.
Growler

interesting stuff there, never knew about the old bi-metallic voltage stabiliser allowing for temperature

I've never noticed the gauge reading more or less accurately since changing to semi-conductor voltage stabiliser in summer or winter but I've not accurately checked and have always treated the gauge as just that a gauge

when I get near or below the quarter mark on the gauge it seems to take about the amount of petrol I expect to fill it summer or winter

I'm not disagreeing just saying I've not noticed

I will disagree with the car not having much heating, with the cooling/heating system in good condition the heater matrix gets very hot
Nigel Atkins

Well... it's subtle. Full will still read as full, empty as empty, but at 0C you may find the gauge drops from full pretty quickly, whereas at 30C it hovers on full for quite a few miles. At least, it does in the Mini. In winter it always felt like it was using more fuel- hitting half full at 300km rather than 350.

I shouldn't really comment on the heating- mine was a Mk1 with no side windows and little in the way of insulation.
Growler

I used to find the fuel gauges were most accurate around the half a tank mark but I find mine is accurate to my expectations when before or after the quarter tank as that's where I fill, before the quarter if my wife is in the car (well before the half if she complains enough or just orders me) and below the quarter when she's not in the car

I always fill until I can see the petrol in the filler pipe, bad habit I know, which takes the needle over full

ever since Peter Burgess done the rolling road set up I've not really bothered with economy so I expect the gauge to drop quickly

one thing I have noticed is that if I check the gauge before switching off to park I know when I return and start up the gauge usually shows less, perhaps the electronics?

having said that the midget gauge is more accurate than my wife's modern car and the speedo in the Midget was more accurate too (before the type 9 installation) so these old styles gauges don't have to have vague accuracy

if I remember I'll see if the electronic makes a difference in warmer weather - easy to check in the cold at the moment, very sunny and very cold today and we should get a run in this weekend
Nigel Atkins

Mine never drops below half even when empty (I found out the hard way) I've put mine down to a concave dent in the tank where I think the dreaded previous owner has tried to jack the car up. It's on my list of jobs to do but nowhere near the top of the list yet. I just fill up regularly.

Any suggestions on how to pull the dent out or am I looking at a new tank?
Eamonn Spencer

my car came without a gauge.. so i bought one from a local shop. It came with a sender unit and everything and fitted in the hole nicely.
However there is no smoothing circuit, and as there are no baffles in the tank i can be either completely full or completely empty depending on which corner i'm going around.... its another thing on my list of things to sort out... but near the bottom...

Andy Phillips

I took the car out yesterday, needle in it's new found comfort zone hard against the empty stop. When I got home. I noticed that it was alive again, showing about half full which is where I'd expect it from the last fill-up. Switched the ignition off and then on again, it was still alive! I wonder what it'll do today?
Dominic Excell

corroded earth connection making intermititent contact....thats what i,d put my money on...probably down near the tank...
Andy Phillips

Had a good look underneath yesterday. There is no connector visible - just a wire coming straight out from between the top of the tank and underside of boot floor. Looks like I'll have to check at the gauge end of the electrics first. Tank out if that doesn't sort it. Very pleased with the overall condition of the underside I must say, waxoyled by PO a few months before he sold it to me, no nasty underseal hiding horrors. Really does look good.
Dominic Excell

the sender earths through the tank and the 6 mounting studs...
David Smith

Dom,
there's a few bullet connectors and other connections from sender to fuse, check they're clean, secure and protected, I'd start from sender end under the car as that one is most exposed and make my way forward
Nigel Atkins

Checked all along the line from the tank. In the end I found it was simply a slightly loose connection on the gauge itself. Cleaned the contacts and now it shows full when the tank is full. Miraculous!
Also fitted new needles and jets, and capped off the carb bodies to stop air leaks at the fairly worn spindle (on the front carb especially) Then tuned it, by ear at first, then confirmed with a colortune kit. A good blue flame at all revs. It now sounds like a well oiled sewing machine. Also cleaned all the connections for the reversing lights, which now work, and tidied up wiring under the bonnet. A busy but fruitful day. Must be careful though, I might run out of jobs to do on it and just have to make do with driving it!
Car now ready to drive to my father's funeral next week. He was to have had a ride in it on our next visit... but this will have to do I guess....
Dominic Excell

Sod's Law whichever end you start looking it's the other

discussion elsewhere about Colourtune and it seems I'm not the only one not to get along with them but they do get you near enough allowing for all the variables of wear in the car's systems

I missed why you sent the rebuilt carbs back and fettled yours

you'll always have plenty to do on the car, some find so much they rarely drive them, how about checking, cleaning, securing and protecting all electrical connections and wires - they should keep you occupied for a while
Nigel Atkins

Hi Nigel

I had always been put off using the colourtune due to other people's comments, but thought I'd try as I had one knocking about. Used it to confirm the settings I made by ear, and it wasn't too far out. Just slight tweaking needed, and it also confirmed that all 4 cylinders were well matched colourwise.
I returned the new carbs, as quite frankly they were a great disappointment. The pistons were not matched to the suction chambers methinks, they certainly didn't drop freely, whichever way I turned them or swapped them over. Also while the butterfly closed nicely on the rear, on the front there was a much larger gap showing, and it was therefore impossible to get a reasonably low tickover.
While the "fettled" old original carbs are fine for now, I may well change to a single HIF44 at some stage in the future.
Now need to back the timing off a tad more - slight pinking when accelerating in high gear from very low speed. Then it should be spot on (I hope!)
Dominic Excell

Dom,
the 'new' carbs sound very bad, what on earth did the guy say about them, you were already committed to that chap otherwise I was recommended by a very reliable source to someone else that does the same thing so hopefully no disappointing work like you got

I decided to go with brand new as I was fed up with recon/rebuilt stuff and I'd already kept doing a little bit more each time to my old carbs and still they weren't quite there

I did consider the single carb but didn't fancy my chances of getting the right manifold fit and good quality single carb

I still think the Colourtune is subjective but near enough for most set ups, I'm sure you'll get it set up well for some proper driving then you can decide if you want it a bit sharper or you could be happy enough with the way it is, (many) more miles and use and the required servicing and the car will blossom
Nigel Atkins

Yes, they looked just the job - but were not good at all. I spoke to his wife / business partner, she was apologetic but obviously couldn't comment until they had them back for a refund. Doubt if I'll ever hear what the problem was.
At least the old carbs now work to an acceptable level, will have to see how much of an improvement they make to fuel consumption on the trip to Wiltshire, they were running horrendously rich before, and with the air leaks, it was nigh on impossible to balance and tune them!
Car is now fully serviced, and has had about 100 miles this week in total (all roof down of course!)
Dominic Excell

if they say they'll let you know, or you ask them to, and they don't then that's bad too

anyone can make the odd mistake or wrong items dispatched but if they're decent people they'd admit to it

we had an excellent roof down run Sunday, force of habit I put my hat and scarf on and had to take them off at the end of our street
Nigel Atkins

Eamonn,

Think about the safety issues for a while if you decide to try this.

I had mud daubers plug up the air vent on the tank of a Peugeot 505 Diesel that I used to have. On a long trip, the suction from the fuel pump partially collapsed the tank. I figured that since vacuum collapsed it, air pressure should straighten it out.

So, I stuck a cut off truck tire valve into the vent line, and pumped the tank up with a portable air tank. It worked just fine. Sorry, it has been too long for me to remember how much pressure it took.

But, you are dealing with gasoline rather than diesel, so a rupture could be quite a fire hazard. Also, the tank location in the Puegeot was such that I would have pretty good protection if it had blown up from the pressure.

If were going to do it on a gasoline tank, I think I would drain and remove the tank, and then fill it with water, and ideally then submerge it in water. This is how pressure vessels are tested, so that if they explode, the explosion is baffled by the water. Because water doesn't compress like air, it doesn't have to expand much if it is decompressed.

Of course you would have to let it dry out in the sun for a while when you finish.

Charley
C R Huff

Thanks Charley, great advice except for one point. I'm from the UK. We don't get much sun here. It'll have to be a space heater in my garage to dry it properly.

I did wonder if a suction dent puller might do the job if I cleaned the tank up sufficiently to get it to grip.

Eamonn
Eamonn Spencer

Eamonn,

Sorry about your lack of sun. Yes, certainly try the suction puller first and see if it works.

Charley
C R Huff

This thread was discussed between 03/04/2013 and 19/04/2013

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