Temp and fuel gauges 2.0

[Rescuejeff]

SO went through everything to get good grounds and such...replaced the temp sender, and fuel sender and well...50%. Fuel gauge now works but the temp is still acting weird. Be honest I'm puzzled. The gauge started to work then pegged hot and dropped back to cold. I touched the wire and it's hot as hell on the sender...and the gauge stops putting out power. Take the wire off the sender and then I got power again. I wrapped the sender in Teflon tape to help with grounding issues... Any ideas out there??? Thanks!

 

[DHugg]

quote " I touched the wire and it's hot as hell on the sender" unquote

RescueJeff, if the wire is heating up and it is not engine or exhaust proximity that is heating it, it's gotta be carrying too much current. I dunno for sure about the guts of the temp sender, but a new one shouldn't have a short in a resistor somewhere.

From the attached wiring diagram, note that electrical current to the temp gauge originates at the ignition switch, through a 3 amp fuse, through the fuel quantity gauge, through the temp gauge, through the temp sender variable resistor to ground. Somehow, too much current is travelling through the temp sender wire. but the 3 amp fuse hasn't blown.

When I picked up the CJ7 from the PO, I found that I had fuses of every denomination in my fuse box, most of them incorrect. Worth a check to see if you REALLY have a 3 amp in the right place, or a 25 amp like I had!

 

[Rescuejeff]

Will be checking that as soon as I get get home...I looked at some many different things I may have over looked that one!

 

[Neuner]

With the title of gauges 2.0 I expected to see an attached pic of them in the trash...

Right now mine are for only filling the holes in the speedo so it doesn't look funny.

 

[Fastatv]

quote " I touched the wire and it's hot as hell on the sender" unquote

RescueJeff, if the wire is heating up and it is not engine or exhaust proximity that is heating it, it's gotta be carrying too much current. I dunno for sure about the guts of the temp sender, but a new one shouldn't have a short in a resistor somewhere.

From the attached wiring diagram, note that electrical current to the temp gauge originates at the ignition switch, through a 3 amp fuse, through the fuel quantity gauge, through the temp gauge, through the temp sender variable resistor to ground. Somehow, too much current is travelling through the temp sender wire. but the 3 amp fuse hasn't blown.

When I picked up the CJ7 from the PO, I found that I had fuses of every denomination in my fuse box, most of them incorrect. Worth a check to see if you REALLY have a 3 amp in the right place, or a 25 amp like I had!

I can't really speak here of any year but mine, a 1976 CJ7 but, the Haynes manual was incorrect on the color wire that plugged into the temp gauge. It had the purple and white plugged in ( and per Haynes, this was correct ), but it should have been a solid purple wire. When I plugged in the solid purple, my temp gauge began working correctly. The wire to the sending unit was solid purple, that's what made me think about it. I doubt my CJ7 was rewired and the color was changed, but I guess that is a possibility.

 

[DHugg]

FastATV, you've prompted me to make a check of the wiring under my dash, since my temp gauge hasn't worked since I picked up the Jeep. I'll run a continuity check, a ground check if appropriate, and a voltage check.

Dusty, dirty wires under a dark dash, even if you open it up, and blessedly hard to color-code. Thanks for the idea.

 

[Fastatv]

FastATV, you've prompted me to make a check of the wiring under my dash, since my temp gauge hasn't worked since I picked up the Jeep. I'll run a continuity check, a ground check if appropriate, and a voltage check.

Dusty, dirty wires under a dark dash, even if you open it up, and blessedly hard to color-code. Thanks for the idea.

DHugg, please keep us all informed on what you find as it will be helpful to many...I think! For me, there were three discrepancies in the Haynes in regards to my jeep wiring, a 1976...totally wrong wire colors were indicated in the book, caused me to pull my hair out Anyway, keeps us posted.....

 

[Rescuejeff]

Checked the fuse and it's all the right stuff. So just don't know what to do now....any ideas?

 

[CRETE4U]

I don't think you should have Teflon tape on the sender threads.

 

[CJ jammin]

+2 on not using teflon tape. single wire sensors need a good ground.

 

[DHugg]

+2 on not using teflon tape. single wire sensors need a good ground.

I use a thread anti-seize with a high copper flake content, particularly on places like spark plug threads and the terminus of all heavy-duty grounding wires.

 

[DHugg]

DHugg, please keep us all informed on what you find as it will be helpful to many...I think! For me, there were three discrepancies in the Haynes in regards to my jeep wiring, a 1976...totally wrong wire colors were indicated in the book, caused me to pull my hair out Anyway, keeps us posted.....

Well, I checked as I said I would. I had good grounds everywhere, 1 ohm to the battery negative terminal. I had key-switched 12V inside the red wire connector. I had 12V at the fuel gauge I terminal. But here is the kicker, the critical diagnostic that will tell you about the fuel gauge - I had 12V, no pulsing, at the strap terminal at the fuel gauge and across to the A terminal of the temp gauge. Shoulda been 5 to 7V, pulsing too fast for the analog volt-ohm meter to see.

That tells the tale; the fuel gauge ist kaput!

So I pulled the fuel gauge outa the speedo, and you can see for yourself how you detect a badly-fried fuel gauge.

There is nothing to be done but to buy a pair of new gauges. If I put everything back with only a new fuel gauge, I will have saved a couple dozen bucks but if (there is a good chance) the temp gauge is bad too, I have to do it all over again, pull the whole dash down. False economy!

This fuel gauge hasn't worked since I picked up the Jeep on 9 Nov 2009. But it will now!

 

[Rescuejeff]

Well I pulled all the tape off and still go the same result. Went from cold to hot and then back down to cold. Thing is pissing me off. Wll try the anti-seize next

 

[DHugg]

Well I pulled all the tape off and still go the same result. Went from cold to hot and then back down to cold. Thing is pissing me off. Wll try the anti-seize next

RescueJeff, I'm having the same good luck as you. I checked all the groundings, checked the wiring from the sensors to the input posts of the new Crown gauges, checked the right red wire that feeds 12VDC when the key is turned, and hooked them up.

Nothing worked!

Decided to let my annoyance factor slowly sink until tomorrow, and attack it with a fresh mind.

I will give you a report of every step.

 

[Fastatv]

RescueJeff, I'm having the same good luck as you. I checked all the groundings, checked the wiring from the sensors to the input posts of the new Crown gauges, checked the right red wire that feeds 12VDC when the key is turned, and hooked them up.

Nothing worked!

Decided to let my annoyance factor slowly sink until tomorrow, and attack it with a fresh mind.

I will give you a report of every step.

Dhugg, RescueJeff. Did you find a solid purple wire in the wiring near the area of the speedo cluster that wasn't connected? As I mentioned, when I pulled my speedo, the purple with white stripe wire was connected to the temp gauge...per the Haynes repair manual. anyway, I measured the resistance on the Purple/white stripe wire to the sending unit connector, it read open. I found the solid purple wire, measured it from end to end, basically had zero resistance. Connected the solid purple wire to temp gauge, and has worked correctly ever since. In my case, the Haynes wiring was incorrect. As far as my fuel gauge, haven't gotten to that point yet, I haven't been motivated enough to pull the fuel tank. For now, I carry two gallons of fuel with me...LOL I will eventually repair the fuel gauge issue as well and report my findings. Rick

 

[DHugg]

Dhugg, RescueJeff. Did you find a solid purple wire in the wiring near the area of the speedo cluster that wasn't connected? As I mentioned, when I pulled my speedo, the purple with white stripe wire was connected to the temp gauge...per the Haynes repair manual. anyway, I measured the resistance on the Purple/white stripe wire to the sending unit connector, it read open. I found the solid purple wire, measured it from end to end, basically had zero resistance. Connected the solid purple wire to temp gauge, and has worked correctly ever since. In my case, the Haynes wiring was incorrect. As far as my fuel gauge, haven't gotten to that point yet, I haven't been motivated enough to pull the fuel tank. For now, I carry two gallons of fuel with me...LOL I will eventually repair the fuel gauge issue as well and report my findings. Rick

I ohm'ed the purple & striped wire from the temp sensor to the temp gauge connector, and it was 1 ohm or less; continuity confirmed. There is another wire back there that could be purple, but the colors have faded; all cats look grey in the dark, even tho I had the dash off and a shop light on the work. The 1984 CJ FSM shows a purple wire to the oil pressure gauge, which suddenly stopped sending simultaneously with the discovery of the loose purple-no stripe wire. I think no coincidence!

So far the only accomplishment I can claim is the clean glass over the face of the speedo. Two rainy days forecast early next week, so I will attack it again with another report forthcoming.

 

[DHugg]

Re: Temp and fuel gauges Final Word

Here's my take on repairing fuel and temp gauges:

Insanity: doing the same thing over and over again and expecting different results.

~ Albert Einstein


The Crown fuel gauge had an internal short; trash! I'll try to return them.


For a fuel and a temp gauge, I'll do it myself. I made a dash at a solution over a year ago, with good result. I use the fuel level sensor already in the tank, but for engine temp a better measurement device is a digital sensor, named DS18B20. It goes up to 257 degrees F, hopefully high enough for the AMC 304 .


I have the prototype working at my desk now; took my own body temperature last night to see if my frustration had given me a fever. Nope! Temperature normal.


I'll try to get our admin folks to accept this project in the Jeep Builders' section. My intent is to log enough information that anyone who wishes to do so can duplicate the work.


I'm starting today while I have my dash torn apart in the aborted effort to fix Jeep's poor engineering design for instrumentation.


Denny