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Why isnt my 68 AMX gas gauge working??? |
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348AMX
AMC Addicted Joined: Jul/03/2007 Location: Massachusetts Status: Offline Points: 4165 |
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Posted: Oct/17/2007 at 10:30am |
As you may know I removed my gas tank and restored it this summer. My gas gauge was working fine before I removed the tank. Weird thing about THAT is the ground wire wasnt even there!!! My only guess on that is the sending unit was grounding through the tank surface and frame?
Anyway All I did was remove the sender have the tank pin holes welded up repainted the outside of the tank re-installed the sender re-connected the yellow wire and connected a ground wire to the sender. Now the gas gauge wont move at all from E? I did paint the top of the sender with silver paint but that shouldnt matter if the ground wire is connected to bare metal right?? All my other factory gauges work fine-factory temp works fine so it isnt the instrument voltage regulator and as far as I know the tank sender does not have it own fuse that could be blown(dindt see any blown fuses on quick glance anyway?
if I fill my tank to the top will the gas station pump shut off when it is full or before I can "overfill" it?? Or will it spill out the filler neck?
thanks Edited by 348AMX - Oct/17/2007 at 10:32am |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Ground the sender wire (the one that goes from the front back to the tank sender) - pull it from the sender and ground it to the frame and see if the gauge moves. (key on, of course!)
Make really sure that ground wire is good, has perfect contact with the sender "frame" and then to the car chassis - takes VERY LITTLE corrosion to block that very low voltage and ampherage.
Grounding and ungrounding the wire to the sender should make the gauge move. If not, perhaps there's an issue with that wire running back there - check fuses, under dash connections, etc.
On these cars, that station pump will shut down long before the tank is over full. I only ever fill mine about 3/4 - you can hear the tone change as the tank fills and the "splash" sounds different. I find filling full, I lose gas when I accellerate.......... Edited by billd - Oct/17/2007 at 10:55am |
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CloudyB
Supporter of TheAMCForum Joined: Jul/05/2007 Location: United States Status: Offline Points: 2369 |
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Probably the same thing billd said
But here's a copy and paste from Tony Zamisch from California Classic Amc
Troubleshooting 68/70 Fuel Gauge Problems. If your gas gauge was working OK, but all of a sudden it quits working altogether, or the needle is reading LOWER than the amount of gas that is really in the tank, then this is the fix for you. 68/70 AMX and Javelin fuel gauge test. This will be a process of elimination. Let's start with the gauge itself. Put the car on jack stands and let the rear suspension hang down. Remove the passenger rear wheel. Doing this will give you plenty of access to the fuel tank sending unit. First things first. Is the yellow feed wire connected to the sending unit? If not, make sure the terminal on the sending unit is clean, also make sure the yellow wire socket is clean and that it fits tightly on the sending unit terminal. Check the sending unit black ground wire. Make sure it is clean and connected. Turn the key on and check the gauge. If it still doesn't work, then try this next test. Remove the yellow feed wire from the sending unit. Do not remove the ground wire! Find yourself a 5 to 6 foot long jumper wire the same gauge as the yellow sending unit wire, and strip both ends of the jumper back about 1/2 an inch. Take one end of the jumper wire and push it into the yellow feed wire socket. Bring the other end over to the driver side of the car. Sit in the car, turn the ignition to the "ON" position and touch the end of the wire to any one of the scuff plate screws. What you're doing is "grounding the gauge". If the needle goes all the way past "full", then the problem IS NOT the gauge. if the needle doesn't move at all, then the problem is in the feed wire from the gauge to the sending unit. Here's where it gets interesting. In 70 there was an option known as a "low fuel warning system". It was designed to warn the driver when the fuel level gets to 1/4 of a tank or less. When the fuel level gets to 1/4 tank, a light flashes in the center of the fuel gauge. If you have this system in the car, then chances are this is the reason why your gas gauge won't read at all. If you have a 68 car, or if you don't have the low fuel system in your 69 or 70, then the problem IS the sending unit in the gas tank. (usually the float, or a burned out unit all together) To determine whether or not you have a low fuel warning system, look closely at the face of the fuel gauge. Between the "F" and the "E" will be what looks like a tiny rectangle slot. If you see this slot, you have a low fuel system. It operates off of a relay located under the dash directly right of the steering column, secured to the dash frame with one screw. It has a 4-wire plug off the relay that connects to the back of the instrument cluster circuit board. It is not enough to simply unplug the relay and solve the problem. You MUST COMPLETELY REMOVE the 4-wire harness from the back of the circuit board. The key to doing this correctly is dependent on the orange light wire which is part of this 4-wire harness. Notice how the orange light wire is plugged into a black plastic socket? The socket is held onto the circuit board by one of the nuts that holds the fuel gauge into the cluster. Remove the nut and take off the socket. Make sure you put the nut back on and snug it down! By doing this you have reconnected the original circuit, only without the low fuel system. Put your cluster back in and make sure your main harness plug in connected. Turn the key on and check the gauge. If it works, then your problem was a burned out low\ fuel relay. If you don't want to go searching for an NOS replacement relay (used relays are not reliable, nor are they accurate) then just put you dash back together and leave it alone. Even when the low fuel system is working correctly, it can be a real annoyance as the light will continue to blink until you decide to fill the tank. I believe this was really designed for long trips where you don't pay a whole lot of attention to the gauge as you're cruising along, and starts to blink when you're low on gas, or reminds you to wake up and go get some gas! I hope this helps answer questions on this subject. As you can see, these are fairly simple tests to tell you EXACTLY where the problem is and how to fix it. Good luck! |
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348AMX
AMC Addicted Joined: Jul/03/2007 Location: Massachusetts Status: Offline Points: 4165 |
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If this is a ground wire issue and I touch the yellow sender wire to a ground as described in trouble shooting, will I fry something like the guage or instrument cluster voltage regulator?? If in fact it isnt grounding with the ground wire connected that "test" concerns me a bit Dont want to melt any wires by accident. I still dont understand how the gauge was working before with no ground wire at all?
The other thing maybe is the clips that hold the yellow wire in place along the frame of the gas tank. I didnt have the wire installed in those clips before and I used them after the gas tank resto, one of them is a tight fit squeezing the wire is this possible causing a grounding problem? I guess the easy way to find out would be take it out of the clips.
The factory ground wire connection to the frame is bare metal so I know the connection is good there, but the small tab on the top of the sender was broken off, tried using an alligator clip on the bit that is still there but it isnt working, or at least it isnt making the gauge work. I am just apprehensive about touching the live sender wire to ground if the ground wire isnt actually grounded, if that makes any sense. Hope to get this fixed soon though, everything else is working great for the first time since I have owned the car.
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bigbad69
Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6668 |
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You won't fry anything by grounding the sense wire and checking the gauge activity. The "voltage" regulator for the gauge is really a current regulator. It will protect the circuit for you.
The gauge will not work without a ground return in the sense circuit. Therefore, there must have been a ground path somewhere before you removed the tank. For the gauge to be reasonably accurate, it would have to have been a pretty good ground. If the clips holding the yellow wire were cutting the insulator and shorting the wire, then your gas gauge would have been pinned at full, so this doesn't sound like your problem. The first test you should do is ground the sense wire (with the ignition on) If the gauge moves, the problem is at the tank. If it doesn't move, the problem is at the gauge, or maybe the sense wire has a break in it. Maybe the sending unit was damaged when you re & re'd it, or it is jammed. If you have a DMM, try measuring the resistance between the the stud on the sending unit and the body of the sending unit. Depending on how much gas is in the tank you should read about 10 ohms (full) to maybe 100 ohms (empty). If you get readings in the thousands of ohms, there is something wrong with the sender. It would be difficult to tell if the float is jammed without removing the whole sending unit - a real PITA, especially if your tank is full. When you re-attach the ground wire for the sending unit, use tooth washers under both screws. They will cut through the paint and rust and get you a good electrical contact. |
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69 Javelin SST BBO 390 T10
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348AMX
AMC Addicted Joined: Jul/03/2007 Location: Massachusetts Status: Offline Points: 4165 |
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Fixed the gauge today! After grounding the sender wire nothing happened. Cleaned a small stripped section of the yellow wire and taped and still nothing. Finally cleaned the threaded terminal of the sender plugged the wire back on and the gauge works normally now. SWEET! Thanks for the tips. |
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CloudyB
Supporter of TheAMCForum Joined: Jul/05/2007 Location: United States Status: Offline Points: 2369 |
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Congrads.Isn't it a great feeling when you finally beat it.
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348AMX
AMC Addicted Joined: Jul/03/2007 Location: Massachusetts Status: Offline Points: 4165 |
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Especially when its electrical. When I pulled the 343, I installed a NOS trunk light(ebay) wich was not installed since I owned the car, installed a restored license plate light bought off-where els- ebay, fixed the horn wich didnt work for years, by cleaning the contact ring in the steering wheel and a new relay. The factory temp gauge never worked until I restored the dash and noticed a printed circuit to the temp gauge on the back of the cluster had a break in it-fixed that so factory temp gauge works, and the gauge light thing started after I restored the dash intermittantly and the extra ground wire fixed that. I had replaced all the gauge bulbs 3 years ago when I redid the dash and they are very bright-looks awesome at night-the 140 AMP alternator keeps things nice and lively too. Headlights are very bright and I used Sylvania silverstar headlights. Keeping the ground at the Blower motor clean insures the headlight lights stay bright on an AMX. Weather is nice still so plenty of driving to do before its hibernation for the winter time. Edited by 348AMX - Oct/26/2007 at 2:56pm |
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