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Old 05-15-2011, 10:35 PM   #1 (permalink)
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Default Bad gas gauge or sending unit...????

OK, I hope I'm not overstaying my welcome with my very first post..! We just joined VMF and I've read through other threads on similar topics but none seem to cover this particular situation. My 14-yr-old son and I recently picked up a '66 Coupe Dark Ivy Green I6, that we just upgraded to a 3spd Top Loader (3.03) from the original 'peanut' trans (2.77).
The fuel gauge has never gone above half when filled up, although it seems to read good from there down. We pulled the sending unit (C6Z F-9275-A) and it looks pretty good, the float arm moves freely, no corrosion to speak of. My guess is this is the original unit, if the part number is any indication.

Since the sending unit "LOOKS" good, could this be a gauge problem...? How do I best troubleshoot this....? (I've read enough to know a 'new' sending unit replacement may not be the way to go.....)

Any help would be greatly appreciated...thanks much...!
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Old 05-15-2011, 11:03 PM   #2 (permalink)
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I would remove the sender again and leave the wire connected. Run it through its full range and see what the gauge is doing.
I believe the shop manual has a test for the sender. You should be able to test its resistance at certain positions.
Also, be sure the sender is "adjusted" correctly for the tank...bend the arm to be able to follow the fuel level to the top.
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Old 05-16-2011, 12:23 AM   #3 (permalink)
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Originally Posted by 66Mrazstang View Post
OK, I hope I'm not overstaying my welcome with my very first post..! We just joined VMF and I've read through other threads on similar topics but none seem to cover this particular situation. My 14-yr-old son and I recently picked up a '66 Coupe Dark Ivy Green I6, that we just upgraded to a 3spd Top Loader (3.03) from the original 'peanut' trans (2.77).
The fuel gauge has never gone above half when filled up, although it seems to read good from there down. We pulled the sending unit (C6Z F-9275-A) and it looks pretty good, the float arm moves freely, no corrosion to speak of. My guess is this is the original unit, if the part number is any indication.

Since the sending unit "LOOKS" good, could this be a gauge problem...? How do I best troubleshoot this....? (I've read enough to know a 'new' sending unit replacement may not be the way to go.....)

Any help would be greatly appreciated...thanks much...!
Switch the fuel and temp wires. if the temp gauge only goes half way then its the fuel sender, if the fuel gauge doesnt points like the temp gauge should , then you have a faulty fuel gauge. Both gauges are the same with different markings.
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Old 05-16-2011, 05:44 AM   #4 (permalink)
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if u ground the wire going to the sending unit(make sure its bare metal) guage should peg-=full. if guage doesnt go to full its the guage. wes
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Old 05-16-2011, 06:59 AM   #5 (permalink)
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well and lastly...the surefire way to test the sender is with it out of the take and with a volt meter, you can ohm it out and check the reading through it's travel to see that it's at it specified upper and lower limits (I forget what the #'s are off the top of my head, but they're easily obtained)
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Old 05-16-2011, 07:07 AM   #6 (permalink)
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…you can ohm it out and check the reading through it's travel to see that it's at it specified upper and lower limits (I forget what the #'s are off the top of my head, but they're easily obtained)
No they're NOT easily obtained. I know, I spent days calling all over the country looking for that info last summer. It's practically a secret.
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Old 05-16-2011, 07:20 AM   #7 (permalink)
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No they're NOT easily obtained. I know, I spent days calling all over the country looking for that info last summer. It's practically a secret.
Really? I put all autometer gauges in my gauge cluster, and when it came time, I found the empty/full readings all over this site, all ford mustangs, ebay, whatever.... 73 empty, 10 full I believe

AUTOMETER 2 5/8" ULTRA LITE FUEL LEVEL GAUGE FORD MOPAR | eBay
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Old 05-17-2011, 03:18 PM   #8 (permalink)
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What great responses...!!..but I'd liket to get some clarifications on several of them....


"I would remove the sender again and leave the wire connected. Run it through its full range and see what the gauge is doing. "
JOE - the sender is still out. Should we re-attach the wire, reconnect the '"-" battery terminal and manually adjust the float...?

"if u ground the wire going to the sending unit(make sure its bare metal) guage should peg-=full. if guage doesnt go to full its the guage. wes"
WES - this is the easiest suggestion, but I want to get it right. You literally mean to just 'short' this wire to ground and watch the gauge...?


Lastly, not sure about switching fuel and temp wires....?? Do you switch them at the back of each gauge...


THANKS ALL,
Joe
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Old 05-17-2011, 04:09 PM   #9 (permalink)
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Fuel gauge reading/tests. In my 68 Mustang and other shop manual this info is obviously not in the fuel section. It's carefully hidden in part 15-3 Instrument Cluster, etc. Careful reading from 15-34 through 15-41 will disclose resistance readings at the two float extremes. I knew it was there from past searches and it still wasn't easy to find. 10 ohm full and 73 ohm empty are the two numbers buried in the text on 15-41.

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Old 05-17-2011, 04:23 PM   #10 (permalink)
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yes-with the key on and battery connected u can test guage by grounding wire that goes to sending unit and guage should peg-if not the guage or wiring from guage is faulty. wes
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Old 05-17-2011, 05:10 PM   #11 (permalink)
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99% chance there is a small hole in the float.....it will be partially filled with fuel. remove, shake and well, you know!
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Old 05-17-2011, 05:15 PM   #12 (permalink)
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As I recall the intitial posting concerned the gauge being way off, not that it didn't work at all. Seems as though part of the issue involves calibration.
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Old 05-17-2011, 06:40 PM   #13 (permalink)
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Quote:
Originally Posted by 66Mrazstang View Post
Lastly, not sure about switching fuel and temp wires....?? Do you switch them at the back of each gauge...

THANKS ALL,
Joe
You have 2 wires on the back of each gauge,
One is the sender and the other is the power supply. Switch the sender wires from the temp, fuel, or oil.

All the gauges work the same, and all the senders run 10-80 ohm range.

So hooking any sender wire to any gauge will have the needle point in the same area. you get the idea.
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Old 05-22-2011, 02:37 PM   #14 (permalink)
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99% chance there is a small hole in the float.....it will be partially filled with fuel. remove, shake and well, you know!
Thanks Jeff, I was hoping for the 'easy' fix, too, but no dice. The float, for as old as it is, is dry... :-)
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Old 05-23-2011, 08:55 PM   #15 (permalink)
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Originally Posted by jmd66fb View Post
I would remove the sender again and leave the wire connected. Run it through its full range and see what the gauge is doing.
I believe the shop manual has a test for the sender. You should be able to test its resistance at certain positions.
Also, be sure the sender is "adjusted" correctly for the tank...bend the arm to be able to follow the fuel level to the top.
Joe
OK, I'm at a loss..... While the sending unit was installed the gauge registered up to half a tank, but no more... Now with the sending unit removed - but still hooked up (battery connected, key on) we get no signal to the gauge at all....always on empty.

I was expecting to get some sort of response from the sender to the gauge (at least 'half'), but it's not happening. I'm figuring I'm doing something wrong......

If we go with the voltmeter, do we test it while connected to the car wire, or is it tested 'dry' - unattached from the car.....
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