My gas gauge reads way over full and the tank is empty around a half a tank. It is pretty consistent in terms of usage, in other words the gauge is not subject to wide fluctuations making it usable to me because I know this quirk. However, I am thinking of upgrading my gauge pod to full gauges and am kind of looking to this as an excuse to the wife (but honey I have to fix the gauge). Do you guys think it is the gauge or the sending unit or something else? Has anyone else experienced this problem.

Thanks
Brad

Usually the "super-full" reading is caused by an open sender line, a bad fuel sender, or a bad sender ground. Take the sender wire going to the tank and disconnect it. Touch that wire to a good ground. The gage, with the key turn to ON, should go to empty. If it does the problem is back by the tank.
If that works, measure the sender between the output pin and the frame of the sender. If you have around 45 ohms (half tank), suspect something with the sender ground wire. If the measurement reads open, looks towards the sender as a problem.

But you're right in thinking that this may be the ideal excuse to go for a full gage panel too. Kinda like the 305 is using oil, gotta get a 350 (383?) ;-)

Thanks for the advice John, I'll give it a try this weekend.

Here is the schematic of the fuel gauge circut:

Instrument Panel: Indicators Cluster (http://elcaminocentral.com/users/elcamino/schematics/indicators_cluster_2.jpg)

A 100 ohm Radio Shack potentiometer is helpful in troubleshooting fuel sending unit problems.

Ok I also had this problem. So following the advice I re grounded and still no change. I also unpluged the wire going to the sending unit all together and still no change. I allso grounded the sending unit wire and no change. I regrounded the the ground wire coming off the sending unit going to the frame and no change. The key is in the on position but I can't see a guage movement. Could it be the gauges its self? The gauge reads over full sometimes and sometimes it reads 3/4, and half right now it is sittling on a half I just keep adding 7 bucks a day and it kinda getting old. Any help greatly appreciated. thanks Corey

With the sender disconnected:
Try grounding the tan sender wire on the gage. See if that drives the gage empty.
Try adding another ground jumper on the black gage ground. See if that changes anything.
Measure the pink gage wire to ground. See if that has 12 volts on it with the key on.
The 1/4 tank off reading may indicate something is wrong with the resistor on the back side of the gage. The white ceramic looking thing with the colored stripe area. If everything above checks out, try another resistor. You can get these off just about any GM vehicle. Found mid-70s trucks fairly easy to get to. Color of the stripe doesn't matter.

Me too. My fuel guage can't seem to get it right consistantly. Sometimes it reads fine for a week or so then it pegs at overfull and stays there for a couple of weeks then start reading fine again. I took off the guage on a junkyard jewel trying to get to some other wiring. The guage on the idiot light cluster has a couple of bare screws that slip into some sockets. no real wires as such. I guessed that the sockets may be a loose fit and sometimes makes a good connection and sometimes loose the contact. Does this sound plausable?

77sprint, i have the same problem in my 77 and am trying to figure it out. My guage just stays at full all the time, even when empty! I took the bezel off and moved the needle all the way to empty then turned the key to the on position, it ran to full and stopped, but wont ever change. Hope fully i will have this problem figured out in the next two days and will report any change. Also just some technical mumbo-jumbo, the resistor on the back of the guage is 85 ohms, in case anyone wanted to know that!

With the sender disconnected:
Try grounding the tan sender wire on the gage. See if that drives the gage empty.
Try adding another ground jumper on the black gage ground. See if that changes anything.
Measure the pink gage wire to ground. See if that has 12 volts on it with the key on.
The 1/4 tank off reading may indicate something is wrong with the resistor on the back side of the gage. The white ceramic looking thing with the colored stripe area. If everything above checks out, try another resistor. You can get these off just about any GM vehicle. Found mid-70s trucks fairly easy to get to. Color of the stripe doesn't matter.

Still trying to get this gauge figured out. My 82 elky I took the whole assembly out I have dummy lights on dash. I measured all three points where the gauges sit in there and none of them measured 12v with key on or off is this right?? And if so where do I go from here I have pulled the wire off the sending unit and grounded it and no change I retapped and grounded the gounging wire that was going to the frame from the tank the gauge sits past full but it is only sometimes it goes to half too kinda seem like it does what it wants.

Look for ground between the tank and rear bumper.


If the problem isn't new, maybe a previous changed the tank. A 17 gallon sending unit in a 22-gallon take with read high.

No the problem is not new I have been just dealing with it. The car is going to paint this friday and I am trying to get all mech ironed out. I already put new ground from tank to back bumper/frame. I have taken the dash completly out today with no results I will prob finish it when I get the new MC SS dash with gauges and see where is goes from there.

I changed the ground a while back, didn't help. I pulled out the sender and it reads the proper 0-90 ohms throughout the range. (Don't ask why I thought pulling the tank would be easier than attacking the gauge cluster first :oops: )

I've pulled out the gauge cluster. I was going to try a new resistor because I have troubleshot everything else.

Now that I've got all that stuff pulled out I think I'll go ahead and upgrade to a tack clock combo with full gauge package. So back to my original question. What do I need besides gauges and tach? I know I need a tach filter. I assume the printed circuit board is different. Anything else? Thanks for all the help.

...So back to my original question. What do I need besides gauges and tach? I know I need a tach filter. I assume the printed circuit board is different. Anything else?

Read this thread (http://elcaminocentral.com/modules.php?name=Forums&file=viewtopic&t=2019)

Search (http://www.elcaminocentral.com/modules.php?name=Forums&file=search) is your friend.

Actually I did search and saw that post. But I don't think it fully answers the question, I believe I will also need a couple of posts to go from the circuit board through the plastic housing for instance. What I was hoping to do was get a step by step on converting from no gauges, blank tach/clock space to guages with a tach/clock combo. I don't want to get half way through it and realize I don't have the "tachamandefiborliator" that they only produced in '85 :D

BTW while I was at the junkyard I went ahead and scored some resistors. They were all over the place as most of the chevy trucks had the gas gauges just lying on the floor, sans needles. I figured no one wanted them and the pull a part lady didn't even charge me. I've got about 3 extras. If anyone wants them send me a message with your address and I'll send one, first come first served. I haven't fully tested my set up yet (just replaced the tank etc before it got dark) but it looks like that was my problem.

Once again a $1 piece failure leads to a day of troubleshooting.

...I believe I will also need a couple of posts to go from the circuit board through the plastic housing for instance. What I was hoping to do was get a step by step on converting from no gauges, blank tach/clock space to guages with a tach/clock combo...
If you currently have just a speedo and gas gauge with idiot lights then you need an entirely new gauge housing. The gauge housings are different for full gauges vs. idiot lights. You can't plug the four gauges into an idiot light housing. You also need the tachometer mounting plate, an oil pressure sending unit, and a temperature sending unit.

sigh

thanks ernie, better bad news than wrong news.

evilbay and the local boneyards (local around here is about 50 miles and I live in the most environmentally backwards state around) don't have a complete set up handy so it looks like I'll just screw the old one back in. oh well, part of me hated to change the original set up anyway.

I always like it when folks say, "just go to the pick a part or boneyard" almost everyone i know crushes anything over 8 years old two weeks after it comes in.