Fuel gauge issues

[Tyre Smoke]

It's a new sender unit. I'm confident it's not the sender unit.

[x 7usc]

Check the tank isn't grounding out on anything (chassis bolts behind) if it grounds out that will make the gauge show full.

[Tyre Smoke]

Hang on, I thought the tank had to be earthed?

[phillpot]

Tyre Smoke said:

Hang on, I thought the tank had to be earthed?

No, the lecytricity jumps from the sender unit back to the battery

[Tyre Smoke]

In that case, might be on to something here.

[Tyre Smoke]

No, not that.

Ordered a gauge from the bay. I've checked everything now, it has to be the gauge.

[ric355]

Tyre Smoke said:

I've got 12v at the sender unit.

My tank is near empty, connect everything up and gauge reads full. Disconnect sender wire from gauge and gauge reads empty. Jump a wire from sender connector on the gauge to earth and gauge reads full. Disconnect earth on the gauge and gauge drops to empty. I'm beginning to think it's the gauge.

It was showing full when I bought the car in October and didn't move. I assumed because of lack of use the float had stuck or dry/corroded connection on the sender unit or elsewhere. Gave the connector on the sender a wiggle and the gauge worked fine for a few weeks. Last weekend and it's back to full all the time.

Are you sure the sender you bought matches the gauge? It sounds like it is working the opposite way it needs to, to me. As I said earlier, full is zero ohms and empty is approx 250 ohms for the gauge. When you ground the input at the gauge that is the same as zero ohms through the sender, so it reads full which is correct.

[Tyre Smoke]

Yep, you're right. The sender works the opposite way to the original TVR one. My original was well worn and had frayed wires on the resistor.

The gauge shows full all the time, which as you say is effectively zero ohms. However, I've no apparent break in the sender wire, but I'll double check.

So I need to get a sender unit from Racing Green, because mine is definitely not well. I do think I can get it to work enough to confirm the gauge is dodgy though.

[Tyre Smoke]

Either way, a new gauge and sender must work!!

[ric355]

Tyre Smoke said:

Yep, you're right. The sender works the opposite way to the original TVR one. My original was well worn and had frayed wires on the resistor.

The gauge shows full all the time, which as you say is effectively zero ohms. However, I've no apparent break in the sender wire, but I'll double check.

So I need to get a sender unit from Racing Green, because mine is definitely not well. I do think I can get it to work enough to confirm the gauge is dodgy though.

You can test the gauge and the wiring as I suggested earlier using a few resistors. They will only cost a few pence to buy as you only need small ones since the current is very low. Anything 1/4watt and less will work fine. All you have to do is turn on the ignition and stick the two pins of the resistor into the multiplug by the fuel tank, or across the back of the gauge (disconnect the input). 125ohms should give you roughly half a tank and you can work other values out accordingly based on the 0-250 scale.

[Tyre Smoke]

I did sort if do that. Stuck my multimeter on ohms and read the sender unit. Original was goosed, well, ok to halfway, then a broken wire. The new one was great, 6 ohms empty, 190 ohms full. But we now know it should be 190 ohms empty, zero (or rhereabouts) full.

My gauge is reading either nothing or full all the time. And the wire between sender and gauge seems unbroken, but I do need to double check that.

Working on the basis that the TVR gauge reads the sender 'backwards' then grounding the sender wire should send the gauge to full (zero ohms) and disconnecting the sender wire from the gauge should send the gauge to empty (190 ohms - large resistance) Am I right? Logic tells me I am, but I did get a U in physics!! If the gauge read the sender at 190 ohms full, and 0 ohms empty (as I was expecting) then grounding the sender should show empty and removing the sender from the gauge should show full. I think.

[LucyP]

If ever there was a - JUST TAKE IT TO A GARAGE AND LET THEM FIX IT case, then this is it.

If I do this, will this happen
If I do that, will this happen
If I do the other will this happen.

I'm all for DIY, and if at first you don't succeed, and all that, but sometimes you have to draw the line.

[Tyre Smoke]

Nope!

I'm not giving up. I can do this. It's a simple wiring issue.

There are only three components. Gauge, sender, wiring. It's one of those. I've eliminated the sender, I will eliminate the gauge (and have a spare ) and then it must be the wiring.

I'll have it all back together and working perfectly by rhe weekend

[LucyP]

There will be a spark before too long and you will blow the car, your garage, yourself, your house, your family and your neighbourhood up. FFS, for the price of an hour's garage labour, just take it to a TVR specialist and let them sort the problem out.

[Tyre Smoke]

There won't be any of that. And it doesn't need a specialist.

But I do appreciate your concern.

[Loubaruch]

If the sender is reading the opposite resistance to that desired are you sure that the float arm is arcing on the correct side of the sender.
I had a similar fault on a Morgan years ago that baffled even the dealer. Fixed the float on the other side of the sender and everything perfect.

[Tyre Smoke]

The sender isn't an arm. It's a metal shaft with a collar that slides up and down.

About to be swapped for a genuine replacement TVR one.

It's either the gauge or the sender and I'm go8ng to replace both for £60ish.

I also have a fuel sender that fits, but sends 'backwards' for a TVR.

[Polly Grigora]

Am well confused now

Poster Chimpongas more often than not posted the facts

The Chimp comments

ChimpOnGas said:

Hi can anyone help me identify the following terminals on my Carbonate fuel gauge?

• one terminal is earth
• one terminal is +12V
• one terminal goes to the sender

But which is which?

Caerbont cunningly just labelled the terminals 1, 2 & 3

I can work it all out with a meter but I was just wondering if anyone was familiar with the Caerbont mystery 123 labelling system.



Thanks, Dave.

and later

ChimpOnGas said:

Sussed it

Just in case anyone is interested here's the terminal layout.

and

Oooops, he couldn't remember

ChimpOnGas said:

The TVR petrol gauge works on a 250 - 0 Ohm range (0 Ohms full & 250 Ohms empty).

The LPG sender works on a 0 - 90 Ohm range (90 Ohms full & 0 Ohms empty).

Or is it the other way round, cant quite remember, but they are definitely working in an opposite way to each other.

This is all very confusing

It would be real good for Tyre Smoke and might prevent Wire Smoke if someone kindly disconnected their cars sender to prove which way round the original gauge and sender do work

The Chimp files https://www.pistonheads.com/gassing/topic.asp?t=12...

[ric355]

Polly Grigora said:

Am well confused now

Poster Chimpongas more often than not posted the facts

The Chimp comments

ChimpOnGas said:

Hi can anyone help me identify the following terminals on my Carbonate fuel gauge?

• one terminal is earth
• one terminal is +12V
• one terminal goes to the sender

But which is which?

Caerbont cunningly just labelled the terminals 1, 2 & 3

I can work it all out with a meter but I was just wondering if anyone was familiar with the Caerbont mystery 123 labelling system.



Thanks, Dave.

and later

ChimpOnGas said:

Sussed it

Just in case anyone is interested here's the terminal layout.

and

Oooops, he couldn't remember

ChimpOnGas said:

The TVR petrol gauge works on a 250 - 0 Ohm range (0 Ohms full & 250 Ohms empty).

The LPG sender works on a 0 - 90 Ohm range (90 Ohms full & 0 Ohms empty).

Or is it the other way round, cant quite remember, but they are definitely working in an opposite way to each other.

This is all very confusing

It would be real good for Tyre Smoke and might prevent Wire Smoke if someone kindly disconnected their cars sender to prove which way round the original gauge and sender do work

The Chimp files https://www.pistonheads.com/gassing/topic.asp?t=12...

Here's an image of the connetions.


I can confirm that the 0-250 ohm range is correct for the gauge, with 0 ohms being full and 250ohms being empty. I can say this with absolute certainty because I have previously tested my own original gauge using the resistor method I described earlier.

[Tyre Smoke]

All of which I can now confirm by trial and error with my trusty £6.99 multimeter (battery not included).

1 is the sender (not difficult to spot it's green and black at both the gauge and sender unit)
2 is earth (again not hard to spot as it loops off the earth for the gauge light)
3 is 12v + (tested with aforementioned multimeter)

My sender reads 190 ohms empty and 6 full. But I know it's faulty.

My gauge is on drugs.