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I'm about to seek counseling over this guage!! The guage pegs to the 3 o'clock position. I've replaced the sender with a new GM one and did a continunity test before I installed it and it was good. The lock ring and mating surfaces on the tank are clean. The ground for the sender is on the trunk and both mating surfaces are clean metal to metal. I took a jumper wire and bypassed the harness so there was no chance of a break and ran it direct to the guage. I tested the voltage going to the guage and its 12 volts. The instrument cluster is grounded to the emergency brake pedal frame and its clean metal to metal. I put a supplemental ground from the cluster to the steering column and added a ground wire to the ground wire that goes to the guage. I even took another stock guage and hooked it up and it does the same thing, pegs to the right. What am I missing? It appears to be a bad ground but where? Anyone know a good witch doctor?

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Mark
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69 Chevelle SS
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When you said you attached the fuel sender ground to the tank, I assume you really meant to the frame.
What happens if you were to take the fuel sender ground and jumper it back to battery negative? This is just a test to see if the frame may not be properly grounded. Sounds like you hit everything else. I also assume you have the ground wire from the battery negative to the right inside fender.
 

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Discussion Starter #3
The sender ground is attached to the body, not the frame. There are 3 ground straps, 2 off the motor to the firewall and one under the passenger side toeboard to the frame. I'll try the jumper to battery negative, and I'll clean the area under the (-) on the fender, its probably painted and not making contact. Where on the frame should the sender ground go, back by the filler neck? Thanks for the help John, I'll let you know what happens.

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Mark
TC#1600
69 Chevelle SS
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There should be a threaded hole for the senser ground wire. Forward and to the left slightly of the tank. Right as you are under the car.
Another thing, you keep pegging right on the gage, full??. Try the same thing with the tan wire that goes to the sender. A solid ground on the tan wire should drive the gage to empty.
 

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Take your meter and measure the resistance from the sender output post to ground. It should be below 90 ohms since 90 ohms is the full reistance. It would be something like 45 ohms if you have 1/2 a tank of gas. If this isn't right, figure out why. It has to be the sender or the grounding wire.

Get a 30, 60 and 90 ohm resistors and use them to simulate the sender to check if the guage is working correctly.

Right now, the guage is grounded to the body and the sender is grounded to the body. No ground straps under the hood are going to help make a better ground between the two.

Peter
 

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Discussion Starter #6
OK, I jumpered the sender ground to battery negative and the gauge didn't move. The same when I grounded the sender to battery negative, gauge didn't move. I jumpered my spare gauge in the system and it pegged to the right. I cleaned the ground to the front fender and cleaned the ground strap from the frame to the body. My autometer gauges work perfectly (they're grounded to the E brake pedal frame) as do my dash lights and windshield wipers. All of this points to a bad ground, but where? Help me obe wan knobi.

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Mark
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69 Chevelle SS
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<BLOCKQUOTE>quote:</font><HR>Originally posted by gotago:
I put a supplemental ground from the cluster to the steering column and added a ground wire to the ground wire that goes to the guage. <HR></BLOCKQUOTE>

Well the problem is around the gage unless the tan wire is no good. What ground wire that goes to the gage? Thought the 69 only had 2 wires on it (tan and pink), or am I thinking of the idiot light car again.
Like Peter says, it doesn't take much to work the gage. If you open or remove the tan wire, at the gage (or at the sender), needle goes full. If you short the tan wire at the gage, needle goes empty.
Since your gage is reading full, take the tan wire to ground. Gage should go empty. Something to try.
 

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Discussion Starter #8
My car is an idiot light car. The gauge has 3 wires going into it, pink on the left(as you look at the front of the gauge), black in the middle, and tan on the right. I grounded the tan wire at the tank to battery negative and the gauge didn't move. I just moved my sender ground from the body to the frame(still no difference). With the switch on,there are about 4 volts going through the tan wire. Is there supposed to be voltage in the tan wire? Thanks ,all, for your patience with me

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Mark
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69 Chevelle SS
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Strange, I thought the 69s only had 2 wires going to it. I dont know if the plug is the same, maybe Elree does, but if you send me your address I can drop a working one out of a 72 your way. At least that will help you figure it out. Don't worry about the money. I have a few. Just pass it on to someone else if they need it when you are done.
 

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This may be a long shot but I was having the same problem on my '64 Elky. The fuel guage never had a correct reading. Finally, I changed the the headlight switch and everything has worked perfectly.
Good luck.
 

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There should be some voltage going to the sender unit. What it is I'm not sure. From what I remember, the voltage on the sender was usually pulsing.

I too thought guages only had 2 wires. Power and sender.

Have you tried a search on the internet for troubleshooting a GM fuel guage. GM used the same basic operational method for years (like 25 or 30 years??) in their fuel guages so there should be something out there.

Peter
 

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Mark, on my 72 Elky the tan wire goes to the gage via the printed circuit. I'm guessing the pink is a switch on power wire and the black should be grounded.

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Discussion Starter #13
Thanks all for the help. John, thanks for the offer, I'll send you my address when I get home(at work now). I guess I'll go back to basics and pull the dash apart and eyeball the grounds and gauge. Since the car was painted and then assembled, maybe something isn't making contact and will look different when I'm not upside down.

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Mark
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69 Chevelle SS
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I have to apologize up front but I have not read in detail all responses so if this has been tried, just ignore me.

I was having the same problem as you did a couple of months ago, drove me crazy. I put new fuel gauge, same thing jumped all the way to full or 3 o'clock and stayed there.

In my case what the problem ended up being was a bad ground cable. I had soltered (yikes, i think this is how it is spelled) the wire to the connectors and somehow the wire broke off inside the jacket and I was not making a ground connection. This was on the ground wire from the fuel cell to the body/frame. Fixed the wire, the gauge started working right away.

Don't know if this helps, but here you have it anyway.
 

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Cares said:
This may be a long shot but I was having the same problem on my '64 Elky. The fuel guage never had a correct reading. Finally, I changed the the headlight switch and everything has worked perfectly.

I too am having troubles with the gas gauge in my 71 and after reading the above post it hit home. My gauge reads mostly 3/4 but does move. When you have the engine and key off and pull on the head lights, the gauge pegs out way past empty and so does the temp gauge above it. Could the headlight switch be causing my gas gauge problems?
 

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Not sure how the 64 fuel gage was fixed by changing out the headlight switch. However, I just sit on the other side of the screen and try and come up with ideas. As I mentioned in this thread the 64 has a poor grounding scheme. Anything could have happened by working under the dash. http://www.chevelles.com/forum/Forum22/HTML/001865.html

Your 71 should be too hard to isolate because the gage does move. Remove the 6 screws out of the dash pad to gain access from the top. On the fuel gage there are 3 wires, the black one being a ground wire. Jumper a wire from the black ground wire to a good frame ground. Pull the headlights on and see if the fuel gage stops jumping. If so, it's a poor dash ground. Since I can't see your car I'm assuming you have a good body ground under the hood. You need a small wire from battery negative to the right inside fender.
 

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Remember that the 64 fuel gauge, is a one year only, and should read 45 ohms when full and not 90. Some retailers think 64 and 65 are the same. Happened to me once.
My ground wire from the front fender to the frame was loose. I went to the next larger sheetmetal screw and added star washers under all my ground wires.
 
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