Tom M'Guinn

This has come up in some other threads, so thought I'd start a new one here. The fuel gauge on my car always tends to read less than full after filling up the car. I've tested the sender in the tank and at the cluster as per clarks, and it is right within spec when full. What I found was that 2 ohms at the ribbon connector showed less than full, whereas with the gauge removed from the cluster, 2 ohm on the input pegged the gauge at full.

So, I was able to get the gauge to read a full needle width higher at a quarter of a tank by cleaning the contact on the center ribbon connector of the cluster with a pink eraser, and cleaning the contact plugs that carry the signal from the cluster to the gauge itself. See the football shaped plugs in the picture. Undo the nut with a 7mm nut driver and clean up both sides of the contacts and the posts that go into the cluster (eraser works well on the cluster side). Will fill up tomorrow to see if this pushes me all the way to the top... Should be pretty darn close.

Someone posted that there was a trim pot on the side of the gauge. I've discovered that some have the trim pot and some don't. If your gauge has a trim pot, know that it makes the gauge read fuller when turned counter clockwise. Unfortunately, when tested with the same signal, the two gauges read exactly the same when the trim pot was turned all the way counter-clockwise -- so at least with my small sample set it looks like the trim pot only acts to lower the gauge vs the no-trim-pot version. Worth turning yours full counter-clockwise if you have one though, assuming your gauge is reading low.

Paulyy

Thanks for this!

My gauge reads 3/4 full when full but i know when my red light is on i've got ~20L left in my tank.

Tom M'Guinn

Here's how I tested the gauge independent of the cluster. I used molex pins (like those sold at radio shack) and had to sqeeze them a pit to fit snug in the gauge ports. Red jumper is 12 volts. Black is ground. White goes through a variable resistor to ground. Idea is to turn the resistor until it reads full, then disconnect and see what resistance it takes to read full. In my case, 2 ohms read full, even though 2 ohms at the edge connector read 7/8 full... Then turned the pot until it read emply and found that is was about 68 ohms, so within spec. Cleaning the contacts between the edge connector and the gauge itself "seems" to have done the trick. Will let you know for sure when I fill up.

Also, with nothing connected, try pushing the needle all the way up, just to make sure it doesn't hit its stop too early. It should swing freely up past the last white line. If it stops short of full, you probably need to remove the needle and re-position it.

Tom M'Guinn

Here's a video showing the gauge working with cluster-free inputs. Full is 2 ohms to ground, empty is about 68 +/- ohms...

joker2cv

Mine gauge reach only 3/4 when full, but for me it's not a problem, because i never fill the tank: it's to expensive here in Italy....

Lex_GTX

The low fuel light is independent from the gauge reading correct?

nofalls

The gauge resistance is by two fingers on a float touching two resistive wires. The red light is off of a contact on the float hitting a contact on the bottom of the assembly. They are independent of each other.

Dougs951S

When the light comes on, roughly how much fuel that is accessible to the pump is left in the tank?

nofalls

If my light comes on I usually still have about 3 gallons. IIRC the tank holds 21 gal and I have to put in ~18 after the light comes on.

Thom

Thanks for that Tom.

Even after cleaning all contact plugs it still wouldn't read full, and I have got the trim pot on full, so what I did was move the needle on its pivot.

FWIW the trim pot should also be present for the voltage gauge if it's present for the fuel gauge.

Tom M'Guinn

One of the gauges I had would reach its mechanical stop at about 7/8, so nothing short of physical intervention like that was going to help. On the little gauges it seems you can just nudge the needle upward to reset the swing range, without having to remove the needle anyway.

Arominus

old thread but bumping to ask, anyone ever notice that the gauges with the pots have an ohm value stamped in them? my fuel gauge has 22ohm, the volt meter pot has 220ohm and the rest have no adjustment.

Would calibrating the pots to these values be worthwhile you think?

Alan 91 C2

Ethanol is gas gauge killer. I have started using some Techron additive.

My Suburban only goes to 3/4 when full.

Good news for their 944, is the sender is easy to replace.

mikey_audiogeek

I always hit the odometer as soon as the fuel light comes on steady.

Then I know I have 100km to go before I run out of gas. Super accurate, have never run out below 100km, ran out at 110 though...

YMMV!

Cheers,
Mike