Getting Back To Fixing My Fuel Gauge

Well this is a much discussed topic, however I have a question. How do you tell if a gauge is blown?

When I do the Ohm checks against this diagram on a gauge that "smoked" because of a bad ground:



I get:
S to Ground (68-72) 71
S to I (19-21) 28
S to A (19-21) 22
I to A (0) 3
I to Ground (49-51) 58
A to Ground (49 - 51) 50

Just received a couple of gauges from ebay, want to check these before I tear into my dash again.

Jon.

 

New Gauge #1

S to Ground (68-72) 71
S to I (19 - 21) 21
S to A (19-21) 21
I to A (0) 1
I to Ground (49 - 51) 51
A to Ground (49 - 51) 51

New Gauge #2

S to Ground (68-72) 71
S to I (19 - 21) 21 100+ - Can't get a steady reading
S to A (19-21) 21
I to A (0) 40
I to Ground (49 - 51) 74
A to Ground (49 - 51) 50

 

How do we feel about putting a 12v - 5 volt stepdown between gauge and ignition wire?

UBEC DC/DC Step-Down (Buck) Converter - 5V @ 3A output ID: 1385 - $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits

So the in-gauge regulator doesn't have to do work.

 

Did you clean the threads on the gauges before you tested them? Slight corrosion or dirt build up can give erroneous readings. Usually readings, greater than 1 ohm, outside the range as describe indicates you may have a bad gauge or a gauge that is in the process of failing. The readings for the original gauge and new gauge #2 indicate they are bad.

New gauge #1 appears to be the best out of the three gauges you have. There shouldn't be a need for a step down converter, the fuel gauge does this. I could be wrong, if you step down the voltage to 5 before it gets to the fuel gauge then there is a possibility that the fuel gauge will step down the voltage even further.

 

I actually did this. Turns out in my case the internal voltage regulator was the issue. In effort to "fix" the situation I lucked upon an old external car CD player that plugged into a cigarette lighter. It had the correct 12V to 5V step down. I wired up one side of a replacement cigarette lighter to a hot wire, plugged in the CD regulator, then wired to the guages. This allowed me to keep the factory guages in place. It's been working fine so far.

To clarify a bit more, you have to disconnect the ignition wire to the CVR and then bolt the 5V hot wire directly to the bus bar (jumper) between the two guages.

The best part about it is the CD player has an inline fuse!

 

The CVR to ground is about the most ridiculous method of grounding ever used. If the gauge is not clamped in place securely or the speedo housing has rust at the point where the CVR touches the housing you will not have a ground for the gauge and it will smoke immediately.

 

Not sure I follow. The guage mounting makes the ground at the dash. That was not changed. I merely inserted a voltage regulator in line with the ignition wire and connected the 5V output to the guage jumper. Therefore it bypassed the factory CVR. No smoke, its been working fine.

 

PGHCJ5 I understand your fix completely. I had typed this up yesterday but forgot to post it. ( sometimers=) Actually the gauge mounting makes it's ground at the speedo housing then the speedo housing to the dash. Some of our jeepers have smoked their new fuel gauges by testing it with the speedo housing assembly not mounted in the dash. Note that the early early jeeps had an external gauge regulator.

 

So I have smoked 2 gauges so far.... the first one was clearly a bad ground issue, the second time I made sure I had a good ground ran a ground wire from the CVR to a known ground point, checked the Ohm readings, etc. Smoked in a few seconds.

Now as I start to install yet another NOS gauge, I am thinking like a safety engineer (belt and suspenders) and considering limiting the voltage input to the gauges to 5V.

 

While tedious, I installed the entire set before I reconnected the hot lead to the battery. Had to uninstall at least twice IIRC because I'd done something NQR. Didn't smoke a gauge, but my temp gauge still isn't right. All readings are correct, so I think the needle is broken (it moves as I drive, with each bump).

Tim

 

Finally getting to this task. I hooked up multi meter to the gauges installed, ohm readings were all correct, So put the volt meter on the fuel gauge back and the gauges are working properly varying between 0-5 volts on the A terminals.

So starting troubling shooting the senders. I made an "ohm generator" using a 0-25 ohm rheostat.



Hooked it up between the S terminals on the gauge and ground. I was able to move the gauge by turning the rheostat and at 25 ohms the needle was at the right place.

So good news, I don't think I have to take the gauges out of the cluster again.

The fuel sender was not generating enough resistance to move the gauge, it maxed out at 14 ohms, so a new one is on the way.

Not sure about temp sender yet

 

Sounds like your getting there.

 

Glad to know I'm not the only one chasing this rabbit.

 

PGHCJ5, jwmckenzie ( or anyone else that knows). I got the UBEC step down you listed as I'm also smoking gauges.
Question, do you know which end of the step down is hooked to batt and which is to gauges??? Step down has red and black wires free on one end and a small pre connect on other. Also I take it red is positive and black negative/ground.
Any help appreciated.
Thanks,
Irish

 

i have closed the subject of my gauge: every 100km i fill the tank!

 

I didnt use the UBEC step-down itself so i cant really say about the wiring. I managed to figure out a "work around" that repurposed some electronics. I'd hate to steer you in the wrong direction. Hopefully someone will chime in about the UBEC unit...

 

Thank you Focker. This gives me something to work with. Will let you know how it goes.

 

Woo-HOO! Found problem. Bad ground at both fuel sender and gauge cluster. Fixed it by running 12 gauge solid wire from negative batt. terminal to a new junction block I set up on fire wall under dash. Then ran seperate grounds to both fuel sender and speedo housing.