Another Faulty Fuel Gauge

Something was wrong! The fuel gauge was reading 1/4 and then it read 1/2 and then.... cough.....engine stopped. It is 40 in the shade in Sydney suburbia 60km from home. Hand primmed it a few time and no fuel! So I sat there while the subtank pumped over, then primmed it again and kept pumping whilst swmbo cranked the engine. Finally she fired up and away carried on to fill it up. This started my investigation. The vehicle is a 2005 GUIV ZD30 Patrol.
Read many posts on the forum which suggested the sender. Bought a new O-ring for the sender and proceeded to remove it and test it. Well it has been in and out 4 times now and I believe it is OK.

This is what I discovered. The tank at the sender is 300mm deep. The sender has a range of 210mm from 30mm off the bottom to 240mm, 60mm below the top. The sender has two parts, a float connected to a variable resistor and a full level magnetic float switch. The float switch is to to stop the sub tank from over filling the main tank. The variable resistor measures the depth: Empty 81 ohms, 1/4:51 ohms, 1/2:30 ohms, 3/4 14 ohms and Full 5 ohms. It is not linear, but follows a reasonably flat curve and for general purposes could be considered linear. (Have you noticed, once your gauge starts moving, it gets to 1/2 faster than 1/2 to empty? Non-linear!

The sender is connected to the Unified Meter Control via a wiring harness running up the passenger side. I still have the problem of the fuel gauge going down to 1/2 or 1/4 then starting to climb back to show about 1/4 tank too much. Frustrating. I have connected a flying lead to the sender wire at plug C123 located behind the passenger side kick panel and an earth wire to test the sender. To date I can not fault the sender, and use a multimeter to check the real fuel level. The fault indicates the Unified Meter Control is faulty or the input resistance is dropping by about 20 ohms.

Can anyone advise me how hard it is to remove and replace the Unified Meter Control? I'm guessing it is located on the back of the gauges. If anyone can shed some more light on my problem, it will be greatly appreciated.

Cheers,
Andrew

Hi Andrew and welcome to the forum, can you pop over to the intro's
and tell us abit about yourself etc. No harm done but just something
the forum asks of us all.
Then hopefully you'll get some answers to your problem

Help Fuel gauge. I am looking for a 2" or similar fuel gauge with an input from 80 ohms empty to 5 ohms full. This is the standard input from a Patrol fuel sender unit. However I have been unable to find an after market gauge with a similar input. Any suggestions appreciated.
Cheers,
Andrew

Before you replace the fuel gauge try doing the extra earth lead mod between the body and chassis.

I don't rely on my GQ gauge at all but fuel warning light works spot on , I go by ks travelled .

I decided to run an earth wire from the fuel sender earth terminal to a point on the chassis. Before connecting the wire I tested the resistance between the sender earth to both the body and chassis. Both measured zero ohms. So, I connected the wire anyway----no change. Still looking for an after market fuel gauge.

Can anyone explain just how hard/easy it is to remove and replace the instrument cluster? I may need to do this to find the fault.

Cheers,
Andrew

A problem that I had with an old Torana was the surface between the sender unit and the fuel tank was rusty. Cleaned up both the tank and sender surfaces and the gauge read right. Worth a look?

The unified meter control is in the instrument cluster. From memory on the series 4 there are only 2 screws in the dash facia around the instrument cluster. Drop the steering column, remove the two screws and then gentle pull the facia towards you. The bottom of the facia is held in by clips that can be stubborn to pop out.

I still don’t think your problem is within the instrument cluster. The symptoms don’t indicated this to me.

Do you have a HF radio or any other EMF producing device fitted to the vehicle?

Quote:

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I still don’t think your problem is within the instrument cluster. The symptoms don’t indicated this to me.

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I have a test point connected to the sender wiring at the passengers side kick panel. Whenever I test the sender resistance it gives me the correct reading in ohms for how much fuel I have in the tank. However, the fuel gauge can be wrong. Where else should I look? I do not believe there is an earth fault in the sender wiring otherwise it would show up at the multimeter test point. Could be a bad connection to the instrument cluster, or in the instrument cluster itself is my guess.

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Originally Posted by Frankrhona

Something was wrong! The fuel gauge was reading 1/4 and then it read 1/2 and then.... cough.....engine stopped. It is 40 in the shade in Sydney suburbia 60km from home. Hand primmed it a few time and no fuel! So I sat there while the subtank pumped over, then primmed it again and kept pumping whilst swmbo cranked the engine. Finally she fired up and away carried on to fill it up. This started my investigation. The vehicle is a 2005 GUIV ZD30 Patrol.
Read many posts on the forum which suggested the sender. Bought a new O-ring for the sender and proceeded to remove it and test it. Well it has been in and out 4 times now and I believe it is OK.

This is what I discovered. The tank at the sender is 300mm deep. The sender has a range of 210mm from 30mm off the bottom to 240mm, 60mm below the top. The sender has two parts, a float connected to a variable resistor and a full level magnetic float switch. The float switch is to to stop the sub tank from over filling the main tank. The variable resistor measures the depth: Empty 81 ohms, 1/4:51 ohms, 1/2:30 ohms, 3/4 14 ohms and Full 5 ohms. It is not linear, but follows a reasonably flat curve and for general purposes could be considered linear. (Have you noticed, once your gauge starts moving, it gets to 1/2 faster than 1/2 to empty? Non-linear!

The sender is connected to the Unified Meter Control via a wiring harness running up the passenger side. I still have the problem of the fuel gauge going down to 1/2 or 1/4 then starting to climb back to show about 1/4 tank too much. Frustrating. I have connected a flying lead to the sender wire at plug C123 located behind the passenger side kick panel and an earth wire to test the sender. To date I can not fault the sender, and use a multimeter to check the real fuel level. The fault indicates the Unified Meter Control is faulty or the input resistance is dropping by about 20 ohms.

Can anyone advise me how hard it is to remove and replace the Unified Meter Control? I'm guessing it is located on the back of the gauges. If anyone can shed some more light on my problem, it will be greatly appreciated.

Cheers,
Andrew

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hi andrew,

did you ever sort out the fuel gauge issue?