Willcox fuel gauge procedure question
Thread Starter
Racer
Joined: Dec 2009
Posts: 456
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From: Homosassa Fl
Willcox fuel gauge procedure question
I determined that my fuel sending unit is bad and ran the checks on my gauge as well. Here's my question: I tested the wire from the tank to the dash per the instructions with the ignition on and the #1 wire removed from the sending unit. The fuel gauge should peg past full to the 3 o'clock and almost 4 o'clock position. Well, mine only goes a needle's width past the full mark. The resistor on back of the gauge reads 95 ohms when off of the gauge.
Do I have a bad or going bad gauge or is my gauge reading close enough?
Do I have a bad or going bad gauge or is my gauge reading close enough?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Still hard to tell but maybe.
The number 1 wire I assume is the ohms wire from the sending unit per my diagram. If you pulled the ohms wire from the gauge it should go full and yes about 3 o'clock.
Did you ground it out? If you grounded it out it should go to empty.
Does the fact that it did not go to three mean the gauge is bad. Not really. So how to you check? Easy.. do you have another resistor? If you have one that is say 45 ohms you can attach it to the ohms wire and ground it out. This should give you 1/2 a tank and so on. You can buy an adjustable linear pot online or at Radio Shack and check the entire scale of the gauge knowing that full is 90 ohms and 45 is 1/2 a tank and 0 is empty. You just dial up the ohms and then insert it inline.
Another idea is to pull a flasher out of the car and use it. (approx 50-54 ohms)
Roger did a post a few years ago showing you how to attach a flasher to the ohms wire for testing and included a fuel gauge picture of the results. You'll find this post on this thread. http://forums.corvetteforum.com/c3-t...post1576946212
While this will only allow you to test at one spot, it will give you a good idea if the dash unit is working fully.
Willcox
The number 1 wire I assume is the ohms wire from the sending unit per my diagram. If you pulled the ohms wire from the gauge it should go full and yes about 3 o'clock.
Did you ground it out? If you grounded it out it should go to empty.
Does the fact that it did not go to three mean the gauge is bad. Not really. So how to you check? Easy.. do you have another resistor? If you have one that is say 45 ohms you can attach it to the ohms wire and ground it out. This should give you 1/2 a tank and so on. You can buy an adjustable linear pot online or at Radio Shack and check the entire scale of the gauge knowing that full is 90 ohms and 45 is 1/2 a tank and 0 is empty. You just dial up the ohms and then insert it inline.
Another idea is to pull a flasher out of the car and use it. (approx 50-54 ohms)
Roger did a post a few years ago showing you how to attach a flasher to the ohms wire for testing and included a fuel gauge picture of the results. You'll find this post on this thread. http://forums.corvetteforum.com/c3-t...post1576946212
While this will only allow you to test at one spot, it will give you a good idea if the dash unit is working fully.
Willcox
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
What year are you working on ? Most of the wire wound resistors I've tested are around 87 ohms on an average,that might be why yours doesn't go to 3 oclock.
If you have a turn signal or hazard flasher,read the resistance between the 2 terminals,check this resistance with the scale ,install on the sender wire and see how your gauge matches.
If you have a turn signal or hazard flasher,read the resistance between the 2 terminals,check this resistance with the scale ,install on the sender wire and see how your gauge matches.
Thread Starter
Racer
Joined: Dec 2009
Posts: 456
Likes: 0
From: Homosassa Fl
What year are you working on ? Most of the wire wound resistors I've tested are around 87 ohms on an average,that might be why yours doesn't go to 3 oclock.
If you have a turn signal or hazard flasher,read the resistance between the 2 terminals,check this resistance with the scale ,install on the sender wire and see how your gauge matches.
If you have a turn signal or hazard flasher,read the resistance between the 2 terminals,check this resistance with the scale ,install on the sender wire and see how your gauge matches.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Roger is referring to the one on the back of the dash unit. Earlier cars had a cardboard wire wound resistor.
Do like Roger said and pull a flasher out and attach it to the ohms wire on one end and then touch it to ground. See if the gauge reads just past 1/2 tank. If you go to that thread I posted earlier you'll see how it's done.
Willcox
Do like Roger said and pull a flasher out and attach it to the ohms wire on one end and then touch it to ground. See if the gauge reads just past 1/2 tank. If you go to that thread I posted earlier you'll see how it's done.
Willcox
Thread Starter
Racer
Joined: Dec 2009
Posts: 456
Likes: 0
From: Homosassa Fl
Roger is referring to the one on the back of the dash unit. Earlier cars had a cardboard wire wound resistor.
Do like Roger said and pull a flasher out and attach it to the ohms wire on one end and then touch it to ground. See if the gauge reads just past 1/2 tank. If you go to that thread I posted earlier you'll see how it's done.
Willcox
Do like Roger said and pull a flasher out and attach it to the ohms wire on one end and then touch it to ground. See if the gauge reads just past 1/2 tank. If you go to that thread I posted earlier you'll see how it's done.
Willcox
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Try putting your ohm meter across the 2 studs that the resistor is attached to. I think it should read around 45,if it reads around 90 that might explain the 1/4 tank reading.
I'm going from memory so we might have to wait for Ernie to show up.
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Race Director
Joined: May 2006
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From: Dayton, Ohio
OK I went out and set up a gauge minus the resistor. It acts just like yours.
Ohms wire ungrounded-the needle goes a needles width past full
Ohms wire running through a 54 ohm flasher=needle goes to 1/4
Your resistor is either open or you have insulating washers on the 6 or 9 oclock studs
Ohms wire ungrounded-the needle goes a needles width past full
Ohms wire running through a 54 ohm flasher=needle goes to 1/4
Your resistor is either open or you have insulating washers on the 6 or 9 oclock studs
Thread Starter
Racer
Joined: Dec 2009
Posts: 456
Likes: 0
From: Homosassa Fl
Thats sounding a little like the resistor on the back isn't making contact.
Try putting your ohm meter across the 2 studs that the resistor is attached to. I think it should read around 45,if it reads around 90 that might explain the 1/4 tank reading.
I'm going from memory so we might have to wait for Ernie to show up.
Try putting your ohm meter across the 2 studs that the resistor is attached to. I think it should read around 45,if it reads around 90 that might explain the 1/4 tank reading.
I'm going from memory so we might have to wait for Ernie to show up.
........................Time for a beer....
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
OK I went out and set up a gauge minus the resistor. It acts just like yours.
Ohms wire ungrounded-the needle goes a needles width past full
Ohms wire running through a 54 ohm flasher=needle goes to 1/4
Your resistor is either open or you have insulating washers on the 6 or 9 oclock studs
Ohms wire ungrounded-the needle goes a needles width past full
Ohms wire running through a 54 ohm flasher=needle goes to 1/4
Your resistor is either open or you have insulating washers on the 6 or 9 oclock studs
Guess I need to do an edit on the help page because I don't think it is there... but a gauge with a blown resistor or one without resistance will only read aprox. 1/4 tank max.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I thought I blew it.. but it is shown on top of page 15 of the help file. There is even a picture showing the needle position.