Fuel Gauge and Temp Gauge problems

[Jake_S]

OK, here's the situation. I bought the jeep with no gauges working except for the speedometer. A month ago, I replaced the temp gauge, for the CVR, and the oil press gauge works, but the fuel and temp gauges don't. I checked the connector for the panel and I'm not getting power to the pins for the gauges.
Does anyone have any ideas that could laed ne in the right direction? I've already checked the fuses and grounds.
Thanks,
Jake_S

[Bob Barry]

Well, the gauges are basically little ohmmeters; those wires from the senders don't carry voltage, but provide variable resistance for the ground, while an average of 5V is fed from the CRV through the printed circuit to the gauges, which heats them up to a certain degree depending on the resistance in the wires. Rube Goldberg couldn't have made it more complex.

First thing to check is continuity at the printed circuit board, from the (+) feed pin on the board to each gauge terminal. It doesn't sound like that is the problem. I would look for continuity in the sending-wire circuits first (check them from the round cluster connector to the sender terminal).

[Jake_S]

OK. Lets see if I have this right. The wires in the connector for the gauges don't carry any voltage, just resistance. So, I need to check the resistance of the PC board to see if I have an open, right? Now if I have an open in the PC board, would my oil pressure gauge work?
The reason I ask is because the oil press, ammeter, and speedo are the only ones that do work.
So, what should the ohmage be fore the PC board between the pins for the temp gauge and fuel gauge?
I apologize for the list of questions, I'm paranoid about running out of gas.
Jake_S

[Stuka]

Hrm, my rig has never run outa gas...gas guage ha never orked...I have just learned how much gas it uses. For the 1st few weeks i put gas in every 3 days..now i know i use about 9.5 gallonss for 5 days or work without outside driving. So I just got used to it ;p

[64Trvlr]

Hey Jake
Fill up your gas tank and write down the mileage. Then when you've got a 100 miles on the tank refill it. Divide the gallons into the miles you drove and you get the miles per gallon. After that it's easy just write the mileage on the gas receipt and drive X miles and put more in. It's easier to do and costs nothing. Or you can just fix the gauge.
:cool:

[Bob Barry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jake_S:
OK. Lets see if I have this right. The wires in the connector for the gauges don't carry any voltage, just resistance.<HR></BLOCKQUOTE>

Right; the 12V(+) is fed through the CVR to the gauges, and the ground for the gauges runs through the sending units. So, you should be checking for continuity on the printed circuit board itself (unlikely a problem), and for resistance between the sending-unit wires in the harness and ground.

<BLOCKQUOTE>quote:</font><HR>So, I need to check the resistance of the PC board to see if I have an open, right? Now if I have an open in the PC board, would my oil pressure gauge work?
The reason I ask is because the oil press, ammeter, and speedo are the only ones that do work.
So, what should the ohmage be fore the PC board between the pins for the temp gauge and fuel gauge?<HR></BLOCKQUOTE>

The resistance won't be between two points on the board, but between the terminal on the sending unit and the chassis ground. For the power-feed from the CVR to the gauge, you're checking for voltage (and it's not a steady voltage, but rather an on/off at somewhat-regular intervals; I suppose you could get an accurate measure with an oscilliscope...), for the wiring from the gauge to the terminal on the sender, you're checking for continuity, and for the sender, you're checking for resistance.

So you should be able to isolate your problem to one of those points in the circuit. Since one gauge is working, your CVR must be working, and since the board itself is unlikely to go bad, I'd imagine the problem is either in the wire to the sender, the senders themselves, the gauge itself, or one of the connectors in the circuit, either at the round instrument-panel connector, the firewall bulkhead connector, or the terminal on the sender itself.

Good luck!

[Crazy_Jeepman]

Ok I like all the ideas on this subject. I on the other hand just carry a spare gas can and when I run out, I pour in the can of gas, and of to a gas station I go. I cant remember how much gas there is in the 3 FSJ's I drive. NONE of the fuel gauges work. Think I will give it a shot and try to fix one, the one in the Wife's 89 would be a good one to fix, this way I may get some piece and quiet..... I doubt it!!!! ;)

[bill tomlinson]

jake_s
welcome!
start with the temp gage: find the sensor on the engine (i THINK) it's near the oil-filler tube abd distributer. jump the wire to ground. turn on ingition. if the temp gage jumps to max hot, you need to replace the sensor. if it does not move from the bottommy guess is that the gage has died...
altho there has been a lot of posts about cracked circut boards...maybe take the gage cluster out and scope with a bright light and
even a magnifying glass. my guess(s) is
1. temp sensor bad, or disconnected
2. gas sender in tank dead: they get more wear than you'd think: as the gas sloshes in the tank the little resistor is moving all the time: wears thru the wire and that's it.

good luck

[Jake_S]

Thanks for the fix tips.
I currently write the amount of fuel and the mileage I fueled up at, and drive about 10mpg worth. I would just like to KNOW what's in the tanks for when I go on road trips to Virginia.
Jake_S

[Jake_S]

Thanks for the help guys. It turns out that both of the sending units went bad. Who would've thought that both sending units would be bad, but the truck is almost 20 years old!
I'll try and hunt down a sending unit for it on Monday.
Jake_S

[Bob Barry]

Cool! :cool:

I'm glad it was something so simple.

[Jake_S]

Thanks again for the info guys. I'm glad it was sometjing as simple as the sending unit. I ws about to replace all the gauges with an aftermarket set.
Jake_S