Fuel Gauge, Wow and Thank you

Took the Morgan out today, first proper drive ever and wow - it felt amazing, I've been waiting for this moment since I first found the car in the barn back in March last year. I wanted to thank everyone who has given me the advice and confidence to get the car to this far - without your help I wouldn't have known where to start.

Taking it to get fuel for the first time it's clear that the fuel gauge isn't working, it hovers at the 1/4 full mark the whole time and I was wondering if somebody could give some pointers as to the logical steps to isolate the issue or where I should look t get replacement parts.

Thank you all again, I hope I can be a net contributor to the site at some point

Great news!

I'd start with the sender in the tank - take the wire off it. Check you have power coming from it.

Then earth the wire - that should move the gauge needle.

If you have power, and the gauge works, then it's the sender.

You can also check the continuity of the wire from the gauge to the sender, and also check the voltage of the wire going to the sender. It should be around 10V, not 12V. There is a voltage stabilizer that provides the feed to the temp gauge and fuel gauge. Is the temp gauge working OK?

Here's the wiring:

I would also check the earth. Earths on mogs often fail.

I am sure MMC use special metals for the earth.
Probably from the group in the Periodic Table ....Rare Earths.
Apologies but I couldn’t resist ( no pun there either).

Very good!

+1

TBM's wiring diagram of the instrument voltage regulator reminds me of the need for same. Late 60's and into 70's and beyond, fuel and temperature gauges worked on the bi-metallic principle where an electrical current would heat such a strip of metal which would distort in a manner proportional to the voltage driving the current, so allowing mechanical linkage of strip to gauge pointer. It also gave very damped readings which was an advantage with fuel sloshing around tank. The technology only worked with a constant reference voltage though, which battery charge systems didn't allow, hence need for 10 volt regulator.

It can be seen if regulation fails an erroneous gauge reading will ensue.

Yep, replaced mine with a solid state regulator - gives me much more accurate temp and fuel readings. Regulator

This site is such an amazing resource - I always come away feeling more educated that when I arrive :-)

The chap at Spiyda makes some really useful stuff, very helpful too

Don't forget that if you are measuring the output of the mechanical voltage regulator it won't read 10V but will chop between 0v and battery voltage (12-14V). The fuel and temperature gauge are heavily damped and take an average. The regulator that TBM mentions is easy enough to install as long as you are the size of a 6 year old child!

Yes, with a modern digital voltage tester they are too sensitive, if you have an old analogue jobbie with a nice old fashioned needle you can almost get a better average reading around 10 volts, but it does flicker a bit, by coincidence been testing one today which suddenly decided to work, I can only assume the coil contacts were a bit grotty from standing over winter

There are other solid state regulators which closer mimic OE.

Thanks for the continued advice from everyone - I used a circuit tester and there is definitely power getting to the fuel tank (the led was flickering, so I'm assuming this is what the flickering from 10v to 0v indicates) - would I find the regulator in close proximity to the petrol gauge.

As the gauge does move (albeit, always to 1/3 full) the uneducated me is going to suggest that it's the sender that needs to be replaced

Got my first ever Morgan Car meet-up tomorrow - so excited !

My regulator was on the bulkhead, behind the glovebox, passenger side (RHD car).

My regulator ('74 4/4 2 seater) is under the dash pretty much dead centre of the bulkhead. Fixed to the inside upper bolt holding the tool tray to the bulkhead. A multimeter would be a good buy. Tests more than voltage.

It's the gauge that requires the regulated 10 volts so it will always be located close by.

An old moving coil analogue multimeter is best to assess the output from an OE electro-mechanical regulator.

. Dai,. A length of bamboo is a lot more reliable.

Ah, bit is it E10 compliant and ethanol resistant ?

How I wish I'd kept my old Avo 8!

I had one of those !!!!!!

David Byrne

When I rebuilt my ‘69 4/4 the fuel gauge always read 1/4 full. I took the fuel sender out of the tank and it was obvious that the arm between the sender and the float had seized up. Application of WD40 to the pivot and gentle load on the float end of the arm soon had it freed off. The gauge now works over its full range. It is of course only an indication that there is fuel in the tank, always best to fill it well before it gets to the empty mark..

I have three having caught the reconditioning bug



This is my very similar AVO 9 but with international markings and measuring up to 3kV. They would need to be sold at £1000 + now if still made, to match production costs given accuracy and complexity of construction.

Note mirror behind pointer to allow parallax correction.

Good man.
I have an AVO8 rescued from work some time before they made me redundant. They didn't ask for it back.

One of the things I wish I still had access to. When I first started work at Plessey Communications in 1980 we had a selection of AVOs and Fluke DVMs in the lab. The AVOs were the most heavily used.

I was at Ferranti in the eighties and remember the excitement when we got a Fluke DVM … revolutionary!

I have a number of test meters (and other equipment), including a Fluke.

I think I found the issue - your suggestions on shorting the connectors made it pretty clear that the problem probably lay in the fuel tank

Here's what I found, looks like the float deteriorated and fell off the sender unit - any recommendations as to where to get a replacement (float or entire unit)

I'm assuming these are specific to Morgans or can I use a universal fuel sender ? The tank appears to be around 8 inches (22 cms deep)


For example, would there be any issues using this float the dimensions seem correct

I could go for the one listed on Morgan Spares of New England, but I've exhausted my budget for the Morgan so I'm trying to do a better job keeping costs under control

Cheers,

Rob

I'd certainly give it a try - a float is a float after all. I'm sure it can be adapted if not a perfect match.

Especially onsidering the Morgan Spares sender is $145 exchange and the Melvyn Rutter one is £120 plus postage. The MR one also looks like a generic one, rather than specific to Morgan so there may be cheaper options out there.

The MR sender has the number stamped TB9006 - 000 on it.

If you google the number, you can pick up a new one for around £30 (same as a Series Land Rover)

Just be wary with generic sender's that it's not for early moving iron instruments circa pre 70's. On these the highest resistance corresponded to full. The later bi-metallic type required reverse.

If in doubt the early type gave instant fuel reading when ignition turned on and didn't require voltage regulator.

To my mind the change to bi-metallic was a step in the wrong direction accepting they gave a damped reading. There was something re-assuring about an instant fuel reading and seeing the needle jump around meant you surely had some fuel in the tank as it sloshed around

Yes, certainly sticker shock with the prices - I've still got to find a roof and repaint the car (as well as a host of other stuff , some yet to be discovered I'm sure )

Phil, your Google search abilities are better than mine, I found one place selling them here but I've decided to risk getting a float and replacement gasket and hope it's a uniform size.

I also scraped the paint of the original sender and found the Smiths Serial number TB 1114 / 028 in case that's of use to anyone.

As always, thank you to everyone for insights and help and my first Morgan meet up was hugely inspiring to keep at it !

Looks a bit like the very early type used in classic Mini's prior to the bayonet style fixing, may be worth searching Mini parts suppliers in the US

That reference is not listed on the current 'Smiths' site, but maybe the similar numbers in the range may help. Scroll down to the TB 1114 section, which refers to Mini as well as Land Rover and others

https://www.smiths-instruments.co.uk/tank-senders

Like many my first serious road car was an 850 Mini YDB 933, 1963 I believe. Question is Jon, did the earliest in 1959 have a moving iron fuel gauge?

Yep, as I said above, a Land Rover series 3 one will work - they also used Smiths gauges and had a voltage regulator.

The generic one from Rimmers is identical to the MR one (jiust £100 cheaper)

Sender (Rimmers)

Sender (Rutter)

I would try to replace the float before trying new ones that 'look the same'

When the sender failed in mine I bought 2 different ones that looked the same, but neither were the same. That presumably is why Smiths had all the different suffixes for different models
They work but the calibration is way out. .

In the end I've bought a Spiyda gauge wizard to balance the calibration (not fitted yet!)

I don't have access to my tech books for a few days, but, IIRC '59 to '64 - '65 had the six bolt mounting, but did use a 10v voltage stabiliser earthed to the back of the speedo