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Unread 11-11-2010, 05:45 AM   #1
bamasteeler
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fuel gauge saga continues

so last week i installed a new fuel gauge and fuel sending unit in my 1980 cj7 and to much amazement it didnt work..haha so i redid all my troubleshooting again and come to conclusion that i got sent a bad gauge (imagine that)!!! so trying to get the new gauge replaced, a guy from quadratec calls and wants to know how i installed the gauge...... so i tell him ummm removed the speedometer assembly and disassembled then removed and replaced fuel gauge????? he says well did you have your battery positive post connected when i plugged up wires on back of speedometer to fuel gauge?? i tell him yes i believe so and he says well they have been gettin a rash of those gauges being burnt up during installation because folks are connecting the wires to them while the batteries are connected. so i ask him what does that have to do with anything cause system is powered off the ignition not straight to battery. or am i just plain old missing some strange law of electrons??? course i get the answer of well i am no engineer but this is what they are telling us. hmmmmm so anybody heard that???

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1980 Jeep CJ7
AMC 258, T176, D300,
AMC 20 REAR, D30 FRONT

1999 XJ CLASSIC
RC 3" front AAL rear
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Unread 11-11-2010, 06:30 AM   #2
wrongway92407
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That's why I get my stuff from 4wd parts. I called told them the same thing and a week later I had a new gauge, no questions ask. Then I sent back the old gauge with an explanation, and about 10 days later I received another gauge. Called them and they sent me a prepaid box. But that was a year ago and it has since gone bad< but are on back order as of last Monday.
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Unread 11-11-2010, 07:58 AM   #3
John Strenk
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Quote:
Originally Posted by bamasteeler View Post
so last week i installed a new fuel gauge and fuel sending unit in my 1980 cj7 and to much amazement it didnt work..haha so i redid all my troubleshooting again and come to conclusion that i got sent a bad gauge (imagine that)!!! so trying to get the new gauge replaced, a guy from quadratec calls and wants to know how i installed the gauge...... so i tell him ummm removed the speedometer assembly and disassembled then removed and replaced fuel gauge????? he says well did you have your battery positive post connected when i plugged up wires on back of speedometer to fuel gauge?? i tell him yes i believe so and he says well they have been gettin a rash of those gauges being burnt up during installation because folks are connecting the wires to them while the batteries are connected. so i ask him what does that have to do with anything cause system is powered off the ignition not straight to battery. or am i just plain old missing some strange law of electrons??? course i get the answer of well i am no engineer but this is what they are telling us. hmmmmm so anybody heard that???

Actually they are somewhat right. If you connect the power to the fuel gauge before you install it into the dash and turn the power on. Then you can damage either the sending unit or the fuel gauge. This is becuase the regulator part of the gauge is not operational without a good ground and there will be no control of the current rushing through the circuit. Of course if your sending units are not connected then there is no problem or if your tank is empty. But a full tank has the least resistance and you can burn stuff up.

NOTE. You do have to have the key in the ON position to burn stuff up. IF the key is in the OFF position no current can flow through the gauge.

Just having the battery cable connected is a crock of doo doo. This is not like a JK were you can blow a computer out with the battery connected and accidentally grounding the wrong thing.Actually they are a little better
protected than that.

Besides, it's poor practice to disconnect the positive cable and leave the ground conneted. You could explode the batery if your wrench comes in contact with the ground when loosening or detaching the positive lead. jnot to mention you will have a handfull of hot wrench.

Just tell him you had the negative cable disconnected.
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Unread 11-11-2010, 09:11 AM   #4
QuickCj
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When I installed my new sending unit I put the float on the wrong side. Therefore my tank was always "empty" because the float was hitting the fuel tank wall. I had to laugh at myself for that one.
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Unread 11-11-2010, 09:21 AM   #5
bamasteeler
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i knew i could get an answer from john..thanks, well lets recap i assembled the fuel gauge into the speedometer obviously outside of the jeep on a bench where oh yeah my entire dash was laying at the time..haha add into it that once i reinstalled it the dash into the jeep ignition was off, sending unit was disconnected and tank was empty..so wow i thin i had more than what guy on phone was wanting..haha
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1999 XJ CLASSIC
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Unread 11-11-2010, 09:40 AM   #6
LT1CJ7
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When your tired of dealing with the aftermarket crap and want a NOS gauge, let me know. I have 1 left that I've been saving for 20 years that I'm not going to use. I also have the matching NOS temp gauge.
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Unread 11-11-2010, 10:24 AM   #7
turbogus
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Quote:
Originally Posted by QuickCj View Post
When I installed my new sending unit I put the float on the wrong side. Therefore my tank was always "empty" because the float was hitting the fuel tank wall. I had to laugh at myself for that one.
Somedays we all can feel those donkey ears spring up
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
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Unread 11-11-2010, 10:27 AM   #8
turbogus
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From other forums I've seen that modern replacement gauges are twitchy to say the least, so we have to do everything 'by the numbers' so's not to burn up these modern day gauges. Not to say OE fuel gauges won't burn if 12v goes to the sender post! My own donkey ears on that one.
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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Unread 11-11-2010, 11:13 AM   #9
John Strenk
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Quote:
Originally Posted by turbogus View Post
... Not to say OE fuel gauges won't burn if 12v goes to the sender post! My own donkey ears on that one.

been there, done that....hmmm... need a T-shirt though.

Let see a snappy saying is needed, something like "AMC Jeeps- the Dukes of Darkness". That works 3 ways...
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Unread 11-11-2010, 11:39 AM   #10
bamasteeler
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so should the ground for sending unit be on the frame or is tub ok? reason i ask is mine is grounded to the tub at same place where my rear marker light is grounded. i assume its good ground cause marker light works great but have read that sending unit is usually grounded at frame.
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Unread 11-11-2010, 12:06 PM   #11
John Strenk
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It should not make a difference but I grounded my sending unit to the dash. Can't trust anything else on mine.
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Unread 11-11-2010, 12:54 PM   #12
bamasteeler
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good thing bout being in the aviation business is lots of extra wiring. we just finished a refurb on our helicopter so now i have lots of nice big electric feeder cables that i am gonna use for putting grounds throughout the jeep. haha
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Unread 11-14-2010, 05:57 PM   #13
bamasteeler
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well i installed my new fuel gauge today and when i turned key to on the gauge actually moved off of below empty to empty..wooohooooo so i drove down the road and filled it up. i know i got a 15 gallon tank and ended up taking 11 gallons to fill it. and wohooo my gauge went up to full. but makes me wonder about the bottom end cause if i still had 4 gallons in it i shouldnt have been reading empty. maybe a little bending of the float is in order but wanna see how it acts on this tank and make sure it reads through the entire range. keeping my fingers crossed!!!!!!
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AMC 258, T176, D300,
AMC 20 REAR, D30 FRONT

1999 XJ CLASSIC
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Unread 11-15-2010, 07:52 AM   #14
turbogus
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Mine performs the same way after gauge repair over two years ago, at least it's constant. I think to get it right on I'd have to adjust the sender in the tank. I'll attend to that if I have other issues that require the tank to be removed in the future. 'Till then, I've just been considering that I've got a good long reserve.
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The parts shop that stocks part for Skylab II will not have parts for our year/model of Jeep
We cannot accurately judge the trajectory of a speeding critter (cat, dog, sasquatch)
Record heat waves and floods only occur when we visit that area
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Unread 11-15-2010, 08:16 AM   #15
walkerhoundvm
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Originally Posted by bamasteeler View Post
i know i got a 15 gallon tank and ended up taking 11 gallons to fill it. and wohooo my gauge went up to full. but makes me wonder about the bottom end cause if i still had 4 gallons in it i shouldnt have been reading empty.
I posted a question a while back on the actual carrying capacity of the 15g tanks, because mine is the same way. The only answer I got from someone who's tested it is that an empty tank holds a little more than 13 gallons. Some portion of the gas exists as actual gas and displaces any volume of liquid you might be able to add to make it 15g. Some of that vapor surely condenses back into liquid as the tank goes down, but practically a 15g tank may only hold 13g+/-.
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