Gas gauge problems

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plymouth71

plymouth71

The Moomobile
Joined
Jun 6, 2010
Messages
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Location
London ky
Hey guys,I am having some problems with my fuel gauge on my 71 scamp.Here is the problem...I have replaced the pc board on the cluster along with the voltage limiter,the temp gauge works fine but I can't get the fuel gauge to work.I have a dim bulb reading on my circuit tester but it doesn't pulsate,the temp doesn't either but it's working good.If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge.The sender is fairly new from classic ind,but I haven't done a ohms test on it yet.Have I missed something?Thanks
 
did the gauge work before the cir board change with the new sender?
 
plymouth71 said:
.If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge.The sender is fairly new from classic ind,but I haven't done a ohms test on it yet.Have I missed something?Thanks
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You are staring at the problem, ohm it out and prove it
 
Dana67Dart said:
did the gauge work before the cir board change with the new sender?
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It did,but it wasn't accurate,I dropped the tank and seen the float was not at the bottom of tank,I bent the arm to set float about 1/8 from tank bottom
 
plymouth71 said:
Ok,I should have done that first,but I figured it was Good since it wasn't very old,that's what I get for figuring
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plymouth71 said:
It did,but it wasn't accurate,I dropped the tank and seen the float was not at the bottom of tank,I bent the arm to set float about 1/8 from tank bottom
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Forgot to mention I have checked the grounding strap,it seems to be good,and when I used an alligator jumper from sender to body,the gauge didn't move
 
are you sure the connector is on the tank sender and the ground strap are in place.


You read my mind
 
plymouth71 said:
Forgot to mention I have checked the grounding strap,it seems to be good,and when I used an alligator jumper from sender to body,the gauge didn't move
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Just to be sure... There is a ground strap from engine to body ( firewall) there should be a ground strap from the in tank sending unit metal tube to the fuel line to provide a ground for the in tank sender. at least that's the way it is in 67 may be different in 71
 
Sounds like the body isn't grounded then, though that's bit hard to believe.
If you got the gauge to move to full by grounding to the chassis then you just proved everything but the sender works.
I'd bet you just need a FOR SURE ground, but it could be the sender unless you ohm test that.
It shouldn't be zero but somewhere between 10 and 70 I think it is.
 
plymouth71 said:
.If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge
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Where are you doing this grounding? If the car is a unibody the "chassis" and "body" should be the same
 
Dana67Dart said:
Just to be sure... There is a ground strap from engine to body ( firewall) there should be a ground strap from the in tank sending unit metal tube to the fuel line to provide a ground for the in tank sender.
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I did check the strap from motor to body(visual)also checked the ground up front at grill
 
TrailBeast said:
Sounds like the body isn't grounded then, though that's bit hard to believe.
If you got the gauge to move to full by grounding to the chassis then you just proved everything but the sender works.
I'd bet you just need a FOR SURE ground, but it could be the sender unless you ohm test that.
It shouldn't be zero but somewhere between 10 and 70 I think it is.
Click to expand...
Ok,thanks I will test that
 
When you say "If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge"

are you grounding the sender at the sender to ground?
 
Dana67Dart said:
Where are you doing this grounding? If the car is a unibody the "chassis" and "body" should be the same
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I was told by napa to test the sender wire by grounding it to frame,should move the gauge to full,then to plug sender back up and use same test wire to ground sending unit to body,if the gauge moved then the grounding strap at tank needed to be removed and all contact points be cleaned and re-installed
 
There IS NO frame/ body in Mopars, they are a welded unibody. You are simply making a poor connection. If the gauge thuds to full when the wire is grounded, either you.......

have a broken connector at the end of the wire and it is intermittent

or the sender is bad

or the tank/ sender is not grounded. Hook up the sender "normal" Connect a good jumper clip to the fuel outlet nipple, and make DAMN sure the other end is grounded. If the gauge works you have found it. If not, replace the sender

"What I use" for this kind of testing is a scrap of wire I can run all the way to "up front" and clip it to either battery NEG or something "bare" on the engine, like the carb, or vacuum advance can, etc
 
Dana67Dart said:
When you say "If I ground the sender wire to chassis the gauge reads full,but if I ground the sender to body no reading on gauge"

are you grounding the sender at the sender to ground?
Click to expand...
To test the gauge I ran a jumper wire from sending unit wire on tank to frame,the gauge moved to full,then I put the sender wire back on tank and run a jumper wire from sender base to body to see if that moved the gauge,I was told if it did to clean up the grounding strap at tank,and if it didn't move the gauge that the sending unit was bad.This is according to napa,I'm not real sure on this imfo from napa?
 
plymouth71 said:
I was told by napa to test the sender wire by grounding it to frame,should move the gauge to full,
Click to expand...

If you ground the sender wire removed from the sender to ground (chassis, frame etc) you should peg the gauge (doing so for more than a few moments can fry the gauge)

plymouth71 said:
then to plug sender back up and use same test wire to ground sending unit to body,if the gauge moved then the grounding strap at tank needed to be removed and all contact points be cleaned and re-installed
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If you use the test wire from sender body to ground (chassis, frame etc) and the guage moves (assuming you have enough fuel in the tank) then that indicates you don't have a good ground from tank to ground (chassis, frame etc)

upload_2018-8-20_21-0-0.png



You do have fuel in the tank? like 1/2 tank?
 
67Dart273 said:
There IS NO frame/ body in Mopars, they are a welded unibody. You are simply making a poor connection. If the gauge thuds to full when the wire is grounded, either you.......

have a broken connector at the end of the wire and it is intermittent

or the sender is bad

or the tank/ sender is not grounded. Hook up the sender "normal" Connect a good jumper clip to the fuel outlet nipple, and make DAMN sure the other end is grounded. If the gauge works you have found it. If not, replace the sender
Click to expand...
Ok thanks for all your help,I have called at least a dozen people on this and they have me running in circles
 
Dana67Dart said:
If you ground the sender wire removed from the sender to ground (chassis, frame etc) you should peg the gauge (doing so for more than a few moments can fry the gauge)



If you use the test wire from sender body to ground (chassis, frame etc) and the guage moves (assuming you have enough fuel in the tank) then that indicates you don't have a good ground from tank to ground (chassis, frame etc)

View attachment 1715213075


You do have fuel in the tank? like 1/2 tank?
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About 5 gallons
 
plymouth71 said:
About 5 gallons
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5 on an 18 gallon tank is a little over 1/4 tank. When I got my Dart my dad had replaced the sender with an aftermarket one and it read full till it was about 1/2 tank. You could have a sender to gauge mismatch. Look at classics website and see if there is a fine print about using their sender with their fuel gauge only.
 
Dana67Dart said:
5 on an 18 gallon tank is a little over 1/4 tank. When I got my Dart my dad had replaced the sender with an aftermarket one and it read full till it was about 1/2 tank. You could have a sender to gauge mismatch. Look at classics website and see if there is a fine print about using their sender with their fuel gauge only.
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Will do,thanks again for all your help
 
plymouth71 said:
Any advise on where to get a good sending unit?
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First do as others have said and measure the resistance that the sender is providing to ground.

This chart is from my aftermarket sender vs my NOS sender.

yours should have similar readings at a particular gallons in the tank.

you can see on the chart that the NOS mopar sender is not linear but the aftermarket on is.

Non linear matches OE gauge Linear gives bad readings on OE gauge

upload_2018-8-20_21-9-47.png
upload_2018-8-20_21-11-22.png
 
67Dart273 said:
There IS NO frame/ body in Mopars, they are a welded unibody. You are simply making a poor connection. If the gauge thuds to full when the wire is grounded, either you.......

have a broken connector at the end of the wire and it is intermittent

or the sender is bad

or the tank/ sender is not grounded. Hook up the sender "normal" Connect a good jumper clip to the fuel outlet nipple, and make DAMN sure the other end is grounded. If the gauge works you have found it. If not, replace the sender

"What I use" for this kind of testing is a scrap of wire I can run all the way to "up front" and clip it to either battery NEG or something "bare" on the engine, like the carb, or vacuum advance can, etc
Click to expand...
I haven't tried to hook to battery,will try that tomorrow,Thanks
 
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