Here is a good site on how the older gauges work. It is for CJ's, but I
believe the early YJ 4.2 was the same.

http://web.archive.org/web/200605230...eep/Gauges.htm

This is a Bill ------ link, the original seems to have gone.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Spdloader wrote:
>
> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader

 

Here is a good site on how the older gauges work. It is for CJ's, but I
believe the early YJ 4.2 was the same.

http://web.archive.org/web/200605230...eep/Gauges.htm

This is a Bill ------ link, the original seems to have gone.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Spdloader wrote:
>
> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader

 

Here is a good site on how the older gauges work. It is for CJ's, but I
believe the early YJ 4.2 was the same.

http://web.archive.org/web/200605230...eep/Gauges.htm

This is a Bill ------ link, the original seems to have gone.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Spdloader wrote:
>
> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader

 

I'm guessing that "Red Jeep" meant to attach the clip to the relay _frame_
so he could get to a body ground, but as you know that's far too close to
high-amperage connections for comfort.

On Sun, 19 Nov 2006, DougW wrote:
>
> Especially since the wires on a starter relay/solonoid are hot.
> http://www.prestolite.com/pgs_training/training_4.php
>
> The test for rotted motor strap is battery ground (or frame) to
> the engine block side of the motor mount or somewhere out of the
> fan and belts.

> Lee Ayrton wrote:

>> Jumper from battery negative to starter relay? I can think of a
>> _lot_ of less hazardous places to put a jumper on.
>
>> On Sat, 18 Nov 2006, Red Jeep wrote:
>>
>>> Check the ground from the battery negative to the body. The wire can
>>> corrode inside the connector and look OK from the outside. Use a
>>> jumper cable from the battery negative to something mounted to the
>>> body (horn, starter solenoid).
>>>
>>>
>>> "Spdloader" wrote :
>>>
>>>> I'm scratching my head over this one, but I'm guessing I've got it
>>>> grounded wrong somehow.
>
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

I'm guessing that "Red Jeep" meant to attach the clip to the relay _frame_
so he could get to a body ground, but as you know that's far too close to
high-amperage connections for comfort.

On Sun, 19 Nov 2006, DougW wrote:
>
> Especially since the wires on a starter relay/solonoid are hot.
> http://www.prestolite.com/pgs_training/training_4.php
>
> The test for rotted motor strap is battery ground (or frame) to
> the engine block side of the motor mount or somewhere out of the
> fan and belts.

> Lee Ayrton wrote:

>> Jumper from battery negative to starter relay? I can think of a
>> _lot_ of less hazardous places to put a jumper on.
>
>> On Sat, 18 Nov 2006, Red Jeep wrote:
>>
>>> Check the ground from the battery negative to the body. The wire can
>>> corrode inside the connector and look OK from the outside. Use a
>>> jumper cable from the battery negative to something mounted to the
>>> body (horn, starter solenoid).
>>>
>>>
>>> "Spdloader" wrote :
>>>
>>>> I'm scratching my head over this one, but I'm guessing I've got it
>>>> grounded wrong somehow.
>
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

I'm guessing that "Red Jeep" meant to attach the clip to the relay _frame_
so he could get to a body ground, but as you know that's far too close to
high-amperage connections for comfort.

On Sun, 19 Nov 2006, DougW wrote:
>
> Especially since the wires on a starter relay/solonoid are hot.
> http://www.prestolite.com/pgs_training/training_4.php
>
> The test for rotted motor strap is battery ground (or frame) to
> the engine block side of the motor mount or somewhere out of the
> fan and belts.

> Lee Ayrton wrote:

>> Jumper from battery negative to starter relay? I can think of a
>> _lot_ of less hazardous places to put a jumper on.
>
>> On Sat, 18 Nov 2006, Red Jeep wrote:
>>
>>> Check the ground from the battery negative to the body. The wire can
>>> corrode inside the connector and look OK from the outside. Use a
>>> jumper cable from the battery negative to something mounted to the
>>> body (horn, starter solenoid).
>>>
>>>
>>> "Spdloader" wrote :
>>>
>>>> I'm scratching my head over this one, but I'm guessing I've got it
>>>> grounded wrong somehow.
>
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

My SWAG is that the sender worked fine until you disturbed it and now it
is bust, but that's just my SWAG. As you saw when you pulled it out it is
just a length of fine wire wrapped around a bit of card. The fuel gauge
circuit goes something like this:

[ Gauge ] Sender
B+ >---------[ Voltage ]----[gauge]---/\/\/\/\
[Regulator] ^
|----------> Ground

For yours, the higher the voltage seen by the gauge the higher the needle
indicates. If the ground is faulty or completely open the gauge won't see
any voltage and will just sit. You can check the ground straps from
engine to body and engine to frame (the fuel sender gets its ground from
the frame, not the body) but I'm guessing that if you haven't seen other
electrical problems then chasing the ground won't yield anything useful.

I think that you're going to have to drop the tank again. You'll need to
do that anyway if you want to check the ground connection.

Troubleshooting guide:

http://www.off-road.com/jeep/tech/electrical/gauges/



On Sat, 18 Nov 2006, Spdloader wrote:

> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

My SWAG is that the sender worked fine until you disturbed it and now it
is bust, but that's just my SWAG. As you saw when you pulled it out it is
just a length of fine wire wrapped around a bit of card. The fuel gauge
circuit goes something like this:

[ Gauge ] Sender
B+ >---------[ Voltage ]----[gauge]---/\/\/\/\
[Regulator] ^
|----------> Ground

For yours, the higher the voltage seen by the gauge the higher the needle
indicates. If the ground is faulty or completely open the gauge won't see
any voltage and will just sit. You can check the ground straps from
engine to body and engine to frame (the fuel sender gets its ground from
the frame, not the body) but I'm guessing that if you haven't seen other
electrical problems then chasing the ground won't yield anything useful.

I think that you're going to have to drop the tank again. You'll need to
do that anyway if you want to check the ground connection.

Troubleshooting guide:

http://www.off-road.com/jeep/tech/electrical/gauges/



On Sat, 18 Nov 2006, Spdloader wrote:

> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

My SWAG is that the sender worked fine until you disturbed it and now it
is bust, but that's just my SWAG. As you saw when you pulled it out it is
just a length of fine wire wrapped around a bit of card. The fuel gauge
circuit goes something like this:

[ Gauge ] Sender
B+ >---------[ Voltage ]----[gauge]---/\/\/\/\
[Regulator] ^
|----------> Ground

For yours, the higher the voltage seen by the gauge the higher the needle
indicates. If the ground is faulty or completely open the gauge won't see
any voltage and will just sit. You can check the ground straps from
engine to body and engine to frame (the fuel sender gets its ground from
the frame, not the body) but I'm guessing that if you haven't seen other
electrical problems then chasing the ground won't yield anything useful.

I think that you're going to have to drop the tank again. You'll need to
do that anyway if you want to check the ground connection.

Troubleshooting guide:

http://www.off-road.com/jeep/tech/electrical/gauges/



On Sat, 18 Nov 2006, Spdloader wrote:

> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it grounded
> wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader
>
>
>

--
"I defer to your plainly more vivid memories of topless women with
whips....r"
R. H. Draney recalls AFU in the Good Old Days.

 

Thanks to everyone!
I'll update when I've time to try some of the ideas.

Spdloader




"Spdloader" <askforit@nospam.triad.rr.com> wrote in message
news:a0u7h.44349$39.11843@southeast.rr.com...
> 1987 Wrangler, 4.2L 5spd
>
> Fuel tank is new, sending unit is original, and worked prior to tank
> replacement.
>
> Problem is, with switch on, gauge on dash reads full until tank is almost
> completely empty, then gauge drops down to
> 1/4 mark.
>
> I'm scratching my head over this one, but I'm guessing I've got it
> grounded wrong somehow.
>
> Any ideas?
>
> I might add, there is no rust on this vehicle.
>
> Spdloader
>