Fuel Gauge Trouble
06-23-2011, 12:46 PM
#1
Thread Starter
Join Date: Nov 2010
Location: Washington
Posts: 14
Fuel Gauge Trouble
Hi Everyone,
I was driving my wife's 64½ a few months ago and I got on it a little bit just for a second and I glanced down and noticed that the fuel gauge was on the rise. Now everytime I turn the key on it goes all the way up past full as far as it can go and stays there. This might be a stupid question but I'm wondering, if I have to end up replacing the fuel sending unit is there a different sending unit for the generator equipped cars? I just wanted to ask here because I know I can't trust the parts stores to know the difference. Thanks alot! -Jon
I was driving my wife's 64½ a few months ago and I got on it a little bit just for a second and I glanced down and noticed that the fuel gauge was on the rise. Now everytime I turn the key on it goes all the way up past full as far as it can go and stays there. This might be a stupid question but I'm wondering, if I have to end up replacing the fuel sending unit is there a different sending unit for the generator equipped cars? I just wanted to ask here because I know I can't trust the parts stores to know the difference. Thanks alot! -Jon
06-23-2011, 01:38 PM
#2
4th Gear Member
Join Date: Aug 2007
Location: Houston, Texas
Posts: 1,692
Not sure if there's a different sender for the generator cars, but ....
Before you go throwing parts at it, make sure the wire is still attached to the sending unit you currently have. If not, that's probably your problem, if so, ground the wire and see if the gauge changes. I think grounding should make it show empty, but I could have that backwards ..... Someone check me on this.
If grounding the wire has the desired effect, replace the sender, if not, the gauge may be the problem.
Before you go throwing parts at it, make sure the wire is still attached to the sending unit you currently have. If not, that's probably your problem, if so, ground the wire and see if the gauge changes. I think grounding should make it show empty, but I could have that backwards ..... Someone check me on this.
If grounding the wire has the desired effect, replace the sender, if not, the gauge may be the problem.
06-23-2011, 03:15 PM
#3
4th Gear Member
Join Date: Jun 2006
Location: Fontana, California
Posts: 1,483
Not sure if there's a different sender for the generator cars, but ....
Before you go throwing parts at it, make sure the wire is still attached to the sending unit you currently have. If not, that's probably your problem, if so, ground the wire and see if the gauge changes. I think grounding should make it show empty, but I could have that backwards ..... Someone check me on this.
If grounding the wire has the desired effect, replace the sender, if not, the gauge may be the problem.
Before you go throwing parts at it, make sure the wire is still attached to the sending unit you currently have. If not, that's probably your problem, if so, ground the wire and see if the gauge changes. I think grounding should make it show empty, but I could have that backwards ..... Someone check me on this.
If grounding the wire has the desired effect, replace the sender, if not, the gauge may be the problem.
you're checked- its actually when open it's empty and grounded is full.
06-24-2011, 11:21 AM
#4
Thread Starter
Join Date: Nov 2010
Location: Washington
Posts: 14
Ok thanks. So you're saying it's possible that it is just shorting to ground somewhere? I was a bit suspicious that there might be a wiring issue because I would imagine if the float failed that it would just show empty all the time? Also this car has some pretty dingy wiring as well. Is there a way to test the gauge with a meter to ensure it's working properly?
06-24-2011, 02:58 PM
#5
4th Gear Member
Join Date: Jun 2006
Location: Fontana, California
Posts: 1,483
To do it correctly, you need a decade box or potentiometer to preset Resistance values that will correspond to specific gauge readings (in place of the tank sender unit). from there you attach the resistance to the feed wire from the gauge and the other side of the resistor to ground. As I recall, anything over 100 ohms is full scale and less than 2 ohms is empty. I believe Mustangs monthly had an article about this in their magazine in the last couple of years.
02-07-2012, 04:21 PM
#6
Thread Starter
Join Date: Nov 2010
Location: Washington
Posts: 14
So I installed a new fuel sending unit. I messed up because I was planning on moving the sender around and watching the gauge to see if it was changing anything. I forgot to do that. Anyway, after I installed the new sending unit the gauge went up past full to what looked like a quarter above full. I then bought a new gauge. I tried installing that this morning and when I turned the key on, the needle shot up past full again and I noticed the GEN light was flickering. I could smell smoke. I turned the key on again and could see smoke filling up the gauge itself. I didn't have this problem with the other gauge. I'm not sure what could be going on at this point. Does anybody have any advice on where to look first before I start going through all the wiring behind the dashboard? Thanks!
02-13-2012, 02:54 PM
#8
1st Gear Member
Join Date: Nov 2010
Location: MS
Posts: 57
Sounds like something shorted to ground. Trace the wire back from the sending unit as best you can ans look for obvious problems...like melted to the exhaust or nicked insulation. Voltage regulator behind the dash may also be bad letting the full 12v to your instruments not stepping down to 5v. Check the voltage reading from the wire at your sending unit with it disconnected. Obviously don't keep voltage going to the gauges very long while you are checking things out.
Any of the other gauges acting abnormal?
Any of the other gauges acting abnormal?
02-13-2012, 03:00 PM
#9
4th Gear Member
Join Date: Jun 2006
Location: Fontana, California
Posts: 1,483
Hi Jon,
Just read about your dilemma - tough luck! You need to check your fuel gauge input wire for excessive voltage it should be around 5 VDC. If its higher- that's what's smoking the gauge -time to replace the IVR unit. spend the money for a good part - there is a definite quality issue with the cheaper units.
If it is at 5 VDc, you may have a short on the output that is frying your gauge. With the new tank sender still hooked up check the resistance reading to ground it should be in the range I've already identified for you , if it is, time for a new gauge.- they do go bad after 45+ years.
Just read about your dilemma - tough luck! You need to check your fuel gauge input wire for excessive voltage it should be around 5 VDC. If its higher- that's what's smoking the gauge -time to replace the IVR unit. spend the money for a good part - there is a definite quality issue with the cheaper units.
If it is at 5 VDc, you may have a short on the output that is frying your gauge. With the new tank sender still hooked up check the resistance reading to ground it should be in the range I've already identified for you , if it is, time for a new gauge.- they do go bad after 45+ years.
02-15-2012, 12:43 PM
#10
Thread Starter
Join Date: Nov 2010
Location: Washington
Posts: 14
That's what's strange about it. I just installed a new gauge and that's when the smoking problem started. It didn't do that with the old gauge. I'll check the voltage as you suggested. Also, maybe I screwed something up when I was installing the gauge