Fuel Gauge

[harleyhouser]

My gas gauge will only show 1/2 tank when full even when i switch tanks. I figure it must be a ground problem. Where do these tanks ground at? I was looking underneath today and couldnt really figure out where the ground is.

87 4wd 350

[J Knight]

I had a similar problem, empty was right but when I was full it only read 1/4 on either tank. My problem happen to be a bad gauge.

[hatzie]

Originally Posted by harleyhouser

My gas gauge will only show 1/2 tank when full even when i switch tanks. I figure it must be a ground problem. Where do these tanks ground at? I was looking underneath today and couldn't really figure out where the ground is.

87 4wd 350

The 87-91 TBI tank ground goes from a ring terminal on the frame through the strain relief in the top of each sender along with a fuel pump power and a sender signal wire.

A bad ground will permanently pin the gauge at 3:00 past the F mark. Each tank has it's own ground so it's unlikely they both have partially failed in the same manner.

I would make sure the tank wiring isn't squashed between the bed and the frame on both sides.

If the gauge reads E correctly but 1/2 when you're actually Full then see my explanation below.
If it's stuck at 1/2 and doesn't move... you have a bad gauge or sender.

Originally Posted by J Knight

I had a similar problem, empty was right but when I was full it only read 1/4 on either tank. My problem happen to be a bad gauge.

The problem you're describing is usually a damaged or loose calibration resistor. You'll find the resistor (usually white with a brightly colored center that corresponds to the resistance value) on the back of the gauge can between 2 of the three studs. Time, vibration, and moisture in the air can corrode and/or wear through the thin metal contact surface of the resistor.

When the resistor makes proper contact the needle will sweep to the full range of the gauge. When the resistance changes, from loosing contact, the needle will no longer move to the top of the gauge but bottom is unchanged. When you change the gauge out it works again because the new gauge has a fully working resistor not because the gauge itself was bad. It's possible to fix the resistor by lightly buffing the contact with fine steel wool (for corrosion) or adding washers that are slightly larger than the bottom of the retaining nuts to get by the vibration damaged contact surface.

[harleyhouser]

Thanks for all the replies guys, I will be on the lookout for a new instrument cluster. The only one of the gauges that actually works now is the temp and speedometer, witch is about 20mph off. I'll just bit the bullet and get it all working.

Thanks

[Jeepwm69]

Originally Posted by hatzie

The problem you're describing is usually a damaged or loose calibration resistor. You'll find the resistor (usually white with a brightly colored center that corresponds to the resistance value) on the back of the gauge can between 2 of the three studs. Time, vibration, and moisture in the air can corrode and/or wear through the thin metal contact surface of the resistor.

When the resistor makes proper contact the needle will sweep to the full range of the gauge. When the resistance changes, from loosing contact, the needle will no longer move to the top of the gauge but bottom is unchanged. When you change the gauge out it works again because the new gauge has a fully working resistor not because the gauge itself was bad. It's possible to fix the resistor by lightly buffing the contact with fine steel wool (for corrosion) or adding washers that are slightly larger than the bottom of the retaining nuts to get by the vibration damaged contact surface.

Very interesting. My gauge the other day went from almost full to around 1/4 tank. I'll have to pull the gauge and check that resistor.

[Tucson38]

Originally Posted by J Knight

I had a similar problem, empty was right but when I was full it only read 1/4 on either tank. My problem happen to be a bad gauge.

I had the same experience, replaced the gauge.

[TDS-MN]

I'll agree, I don't think that your problem is a ground. Sender or gauge itself, but it sounds like you have a plan and direction to go. Good Luck!

[Jeepwm69]

Awesome fix! Took my gauge out, cleaned up contacts on that resistor and put some dialectic grease on there and my gauge works again! Thanks Hatzie!
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[Jeepwm69]

annnnnnddddd, now mine's back to reading 1/4 tank. Took the gauge out and put regular nuts on the resistor (push nuts had loosened) and put back in. When I turned the key, the gauge started to go to F, then about 1/2 way there it stopped and dropped back to 1/4 tank. Looks like my gauge is bad or the resistor is shot.

Anyone know if I can get the resistor ONLY somewhere? I'd like to keep my stock gauge if possible.

[hatzie]

Originally Posted by Jeepwm69

annnnnnddddd, now mine's back to reading 1/4 tank. Took the gauge out and put regular nuts on the resistor (push nuts had loosened) and put back in. When I turned the key, the gauge started to go to F, then about 1/2 way there it stopped and dropped back to 1/4 tank. Looks like my gauge is bad or the resistor is shot.

Anyone know if I can get the resistor ONLY somewhere? I'd like to keep my stock gauge if possible.

Ring terminals soldered to at least 2 parallel 1/2 Watt resistors. http://diyaudioprojects.com/Technica...calculator.htm

You could try flat washers with external tooth star washers underneath.

I'll check the ohm value on my good spare gauge tonite.

This article has info on the color vs ohmage on vette gauges. IDK if other's any correlation to our clusters. GM didn't document this for the general public or their techs.
http://www.europeancorvette.com/html/console_gauges.htm

[Jeepwm69]

Originally Posted by hatzie

Ring terminals soldered to at least 2 parallel 1/2 Watt resistors. http://diyaudioprojects.com/Technica...calculator.htm

You could try flat washers with external tooth star washers underneath.

I'll check the ohm value on my good spare gauge tonite.

This article has info on the color vs ohmage on vette gauges. IDK if other's any correlation to our clusters. GM didn't document this for the general public or their techs.
http://www.europeancorvette.com/html/console_gauges.htm

Yeah, interestingly enough I found a similar chart on a different corvette website (bookmarked it on my home computer).

I am ok at soldering so will try that before I spring for a new gauge. Is this something I can get at radioshack or am I going to have to buy online?

[Jeepwm69]

Soooo, tried the star washers. Still nothing. Gauge goes to 1/4 tank and stays there.

Anyone know of a source to get another resistor?
If I get an aftermarket gauge will it have a resistor that will work with the stock gauge (assuming it is the resistor that is bad and not the gauge)?
Can one of you electrical genius types tell me how to MAKE a resistor that would work (I can follow directions on RadioShack stuff if it's written on a 3rd grade level)?

[tucsonjwt]

I appreciate your desire to keep a stock appearance, but it might be easier to buy an aftermarket gauge for Classic Parts for $50 and switch out the gauge faces. I just put the aftermarket gauge in my 83 and left it with the aftermarket gauge face, showing fill markings in icon format rather than E to F.

[Jeepwm69]

Found a resister for a 67-72 pickup for $10. Part number 67-04508 at www.truckandcarshop.com. That work? From what I've found all GM vehicles from 65-early 90's used the same fuel gauge (at least the guts)

[Jeepwm69]

Found this one and am going to try it.

http://www.ebay.com/itm/390024357497...84.m1423.l2649

From what I could find all GM cars from 65ish up use a 0-90ohm fuel gauge (and the 69 camaro does according to all the forum threads I found on the subject) so hopefully this will work.....

I'll report back when it comes in.

[motornut]

check the other ground for the gauge
behind it,behind the cluster
where they all go to one
when i changed over my idiots to gauges issues stopped

[Jeepwm69]

Originally Posted by Jeepwm69

Found this one and am going to try it.

http://www.ebay.com/itm/390024357497...84.m1423.l2649

From what I could find all GM cars from 65ish up use a 0-90ohm fuel gauge (and the 69 camaro does according to all the forum threads I found on the subject) so hopefully this will work.....

I'll report back when it comes in.

SUCCESS! I got the above resistor yesterday and put it on the truck. For anyone searching in the future, I've attached the packaging for the resistor with the part number; W-586 which was advertised as a fuel gauge resistor for a 69 Camaro.

[Jeepwm69]

Not sure what I'm looking for. My truck is an 83 so I have speedo cable, one light on the top passenger side, and a square electrical connector, and that's it. Don't see a ground wire anywhere.

If there is one, where does it ground?

[motornut]

Originally Posted by Jeepwm69

Not sure what I'm looking for. My truck is an 83 so I have speedo cable, one light on the top passenger side, and a square electrical connector, and that's it. Don't see a ground wire anywhere.

If there is one, where does it ground?

Look back from the seat belt buzzer
Ground is black wire in the plug
More then one
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[Jeepwm69]

Originally Posted by motornut

Look back from the seat belt buzzer
Ground is black wire in the plug
More then one
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Ha, don't think mine has a seat belt buzzer. It's an 83 High Sierra. Dad got it pretty bare bones when he ordered it.

[motornut]

Originally Posted by Jeepwm69

Ha, don't think mine has a seat belt buzzer. It's an 83 High Sierra. Dad got it pretty bare bones when he ordered it.

gee and i thought mine was bare bones
thought those were stock
but look about a foot back from the cluster plug
un ravel the friction tape
can't miss it cause it's prob got about 4 + wires together