Justin123shory

I am having a difficult time finding the issue with my gas gauge. It primarily started being stuck beyond full when the key was in the on position, I checked sending unit which turned out fine and was looking at the back of the dash when I touched the voltage regulator(I believe it to be called that) and it sparked which led to the gauge not moving at all. Is the gauge bad or do I have a bad ground somewhere? And how would I check these things? Help please!

moe7404

my factory service manuals have a process to check the gauge and the tank sending unit. but its to long to type. a factory service manual close to the same might have your info. and there are web site with the info you need. and check out stickys on diff sites. i have seen people say that the sending unit i the tank can be helped by useing Marvel Mystery Oil in the fuel. good for the engine to.

pro-tech

More than likely the constant voltage regulator is bad but the way you can check the wiring is to take a test light and give it a good ground...(like right to the battery with a jump lead) Pull the wire off the sending unit and touch probe to the wire at the connector. (purple wire I think could be brown)with the key on it should pulse/flash the test light if it does the dash gauge should go to full..If it doesnt flash/pulse then either the wiring or the regulator is bad...If the gauge goes to full either the sending unit is bad or the tank is not making a good ground...I am assuming you already checked all the fuses which is always the first step and to make sure there is power to them...Bill

440roadrunner

The instrument limiter / regulator feeds both temp and fuel gauge, and if you have a rally dash, it feeds oil as well. If you have a rally dash, the limiter does not plug in, it's built into the fuel gauge.

DOES the temp gauge work? If so, and if it seems to indicate normally, the voltage limiter is not the problem.

There are a number of problems with "gauges." I try to get you guy to think of these as an "end to end system." This system can develop a number of problems................

Switched ignition is fed to the cluster through the harness connector. ANY of the PC board connector pins can break or get loose. You must repair them, or buy a repop PC board.

The IVR "socket" (non rally) has brass springy contacts that MAY not be making contact with the board traces.....you must solder across them

The IVR can be bad. Buy an RTE solid state replacement

The gauge stud nuts can be loose / corroded. Replace the fake nuts with real ones, and loosen / tighten them several times to scrub the connection.

The gauge units could be bad / out of calibration.

The sender wires going to temp, fuel (and oil) could have poor connections at the PC board pins, at the bulkhead (oil and temp) and the kick panel connector for the rear harness for fuel.

They can have bad connections right at the sender connector.

Once you get what you think is "problems" fixed, you can test the whole thing with resistors. The gauge senders are all the same, about 10-13 ohms for full, about 23--25 ohms for 1/2 scale, and about 70--75 ohms for empty.

For example, go to Radio Shack and buy a pack of four of 100 ohm, 1/2 watt resistors. Wire all 4 in parallel, and this gives you 25 ohms. Hook this (example) from the temp sender wire connector to ground, and turn the key to "run" for about a minute. The temp gauge should read about 1/2 scale.

moe7404

i found.
http://www.chargersourceguide.com/

has a guide to make a IC regular. titled- gauges voltage limiter. it is a regular circuit for a LM317. other part numbers will do the same thing. i have a print out of it. but cant find it at there site. i think what roadrunner said is the same thing. it should be easy to build.

moe7404

OK i found it. i think this is the best fix i have seen their are others.

http://www.chargersourceguide.com/voltagelimiter.html.

all so a 7805 chip will work. the diff is the 317lm chip is set at 5 volts with the resistors and cap. but can do other volts by changing the caps and resistors. but the 7805 chip is locked at 5 volt when made. but still needs caps. by using the stock steel can as a heat sink you can get by with out a heat sink normaly used with electronics.

Justin123shory

Thanks for the replies! Sorry I've been offline for a few days but I will definitely get rid of the limiter using the link you gave me because it has also given me problems in the past but before I do that is there a way I can check the gauge itself just to reassure that it's still good?

Justin123shory

Okay so I tossed the limiter and required it using a 5v regulator and a capacitor using this link http://www.allpar.com/history/mopar/electrical2.html .... And I still get nothing out of the gas gauge, I've checked the sending unit, replaced the limiter, so what is my next step to do or is it almost guaranteed to be a bad gauge?

440roadrunner

I don't know what all you've checked. Make sure you actually have 5V right at the gauge stud. Make sure you test by grounding the sender wire, and if that does not work, ground right at the gauge stud

And make sure the cluster is actually grounded. Run a separate pigtail wire from a ground on the PC board(s) to the body, such as the column support

The regulator supplies both temp and fuel, (and oil if present) so if the temp works OK and the fuel does not, it's either a connection, a bad sender wire, or bad gauge.

If you hook a 3V battery (two 1.5 volt cells such as AA or C or D in series) direct to the gauge it should read upscale close to the full mark, about 3/4 - F

Here:

http://www.forabodiesonly.com/mopar/...p?p=1970209465

Justin123shory

Alright I ended up fixing it thanks 440roadrunner, it ended up being the voltage limiter and the regulator I rewired it with was the wrong one so I got a voltage regulator #7805 from radio shack along with a small capacitor and it works now, I need to fill it up to make sure it goes all the way to the top but will keep running it to make sure it goes all the way to empty as well. Thanks!

440roadrunner

COOL!!