Gas Gauge Not Working

[Ghostultramarine]

so, I changed the gas tank yesterday in my 68 Newport convertible.

The gauge was not working prior to the tank swap (figured the old sending unit probably did not work).

I tested the new sending unit prior to putting it in and it seemed to work. (The movement on the ohm meter was not as smooth as in the video showing how to check the unit but it did work.)

What I want to know is what I should be checking, as exactly as possible, when I pull the dash again?

Perhaps how to test the gauge, itself?

 

[CBODY67]

As I recall, the gas tank sending unit is a variable ground type of circuit. Make sure that all connections are clean and not corroded for best results.

 

[Ghostultramarine]

I took time to clean the plug that goes on the post of the sending unit.

I’ll do the same with the dash.

 

[Davea Lux]

Take a test light and hook it to a good ground and the detached lead to the tank sending unit. You should get a flashing test light if the cluster voltage regulator is functioning properly. If you get nothing, either the circuit to the tank is bad or the cluster regulator is bad. Also check the fuse for the instrument cluster. If you get a flashing test light, you either have a bad float on the new sending unit or the tank is not properly grounded. The ChiCom replacement sending units have a lot of bad floats due to poor soldering on the float.

Dave

 

[CBODY67]

At the tank itself, where the short piece of fuel hose connects the chassis-located gas line and the nipple on the sending unit, there SHOULD be a clamp on each end of a piece of metal, with the ends of the tab contacting the metal on the fuel line and also the metal on the sending unit. If that clamp is missisng, you might get a piece of wire and complete the circuit by one end of the wire being on the sending unit and the other on the chassis fuel line.

Those clamps should be in repro, but adding that piece of wire should do the same thing, I suspect. There should be a picture of that clamp assy in the FSM, as I recall.

Enjoy!
CBODY67

 

[live4theking]

^^^^ This what Cbody67 is talking about.

 

[Ghostultramarine]

By Jove, that is missing!

 

[stubs300]

By Jove, that is missing!

2 hose clamps and a piece of wire work for a substitution, AMHIK! Good Luck

 

[77newyorker440]

My Chrysler had the same issue. My dad and I took a ground strap and put one ring terminal around the metal line on the sending unit and put the other on a bolt that holds the mount for the metal fuel line on the frame. Gauge works perfectly now.

 

[Ghostultramarine]

Now that it’s not in the hundreds today, I tried a grounding wire and, voila!, nothing ...

*sigh*

Could be the 18 gauge speaker wire I used (probably not), could be the fact I connected it to the fuel line, not the body, again probably not.

I’ll have to pull the dash apart again. Was going to do it anyway because I keep blowing a fuse when the dash lights come on.

One thing at a time, I guess. I really would like a functioning fuel gauge...

DOH!

Just scrolled up and read about the fuse for the instrument cluster ...

 

[stubs300]

Did you clean everything good to ensure a good ground, or not?

 

[Ghostultramarine]

That’s a good question. The sending unit is new and the fuel line also looks pretty new.

However, now that you are saying that, I suppose it’s theoretically possible it’s not grounded (well).

 

[Big_John]

Here's how you check the gauge...

Unhook the wire at the tank sender and ground it. With the ignition on, the gauge should read "peg"full.

If that doesn't do it, it's the wiring, the gauge or the voltage limiter.

when I pull the dash again

That tells me you had the dash out, so that could be an issue with wiring, like a plug not completely pushed together or something similar with the voltage limiter.

The gauge seldom fails, usually the limiter dies and IIRC, the gas gauge is really the only gauge in the '68 Chrysler so that means the only gauge controlled by the limiter (ammeter isn't).

The next best place to check the gauge without going under the dash is the plug going down the left side, and I believe it should be under the left kick panel. Again, disconnect and ground to check gauge.

My money is on the voltage limiter and I can't tell you a good, easy way to check the output (5 volts) from the limiter. If anyone does, chime in. IMHO, the limiters are pretty much shot most of the time anyway and a new electronic replacement is an excellent upgrade that makes the gauge more accurate and reliable. I don't want to spend your money though.


Here's a couple pics I found showing the limiter. These guys sell electronic versions: RTE limiter - rte I believe you want the IVR3, but you need to follow up and double check that.

 

[Ghostultramarine]

So I went for a cruise tonight (Not always the most fun without a working fuel gauge) and the dash lights did not blow a fuse.

Made me wonder if the grounding wire helped in some way (IF they are on the same fuse) but the fuse blowing started before I changed the tank.

How can you bench test an instrument cluster relay? (If I’m taking the dash apart I might as well test it.).

 

[Ghostultramarine]

Big John, thank you for all the help.

I note the price of the dash regulator varies greatly.

IVR607 - 1966-74 Mopar A, B & E-Body Instrument Voltage Regulator

Mopar Dodge 2258413 Instrument Panel Voltage Regulator 19...

 

[Big_John]

Big John, thank you for all the help.

I note the price of the dash regulator varies greatly.

IVR607 - 1966-74 Mopar A, B & E-Body Instrument Voltage Regulator

Mopar Dodge 2258413 Instrument Panel Voltage Regulator 19...

Those are a different style than your car has, meant to plug in rather than connect to. Note also the lack of the mounting bracket on the back.

If you really want to, search around on the web and you see that you can build one yourself if you want. I think Ehrenberg has a decent article on doing it.

Myself, I use something similar to this. Waterproof DC-DC Converter 12V Step Down to 5V Power Supply Module 3A 15W BLACK | eBay

 

[Ghostultramarine]

Take a test light and hook it to a good ground and the detached lead to the tank sending unit. You should get a flashing test light if the cluster voltage regulator is functioning properly. If you get nothing, either the circuit to the tank is bad or the cluster regulator is bad. Also check the fuse for the instrument cluster. If you get a flashing test light, you either have a bad float on the new sending unit or the tank is not properly grounded. The ChiCom replacement sending units have a lot of bad floats due to poor soldering on the float.

Dave

Okay, I tried this today. I made sure I had a good ground (the tank is grounded, by the way, I confirmed that).

To test the sending unit in the tank, do you have to have the vehicle's key turned to 'run'? Not started?

(I had it set to "run" but not started, being underneath it.)

I disconnected the plug that goes over the threaded "screw" sticking out of the sending unit and inserted the pointy end of the test light into the plug and I got nothing.

I used the volt meter on the sending unit while set to 200 ohms and it gave a constant reading (I retested it several times and each time was the same reading).

The gauge seldom fails, usually the limiter dies and IIRC, the gas gauge is really the only gauge in the '68 Chrysler so that means the only gauge controlled by the limiter (ammeter isn't).

Okay, so if the gas gauge is the only gauge hooked up to the limiter, is that the ONLY thing it affects? Or would something else be affected by it?

I'm trying to do one thing at a time and I'm the first to admit that while wiring is logical and makes sense to me, it is not my shining point. So, one thing at a time with simple instructions that do not leave out any steps or make any assumptions that I know what I'm doing. Please.

 

[Big_John]

Okay, so if the gas gauge is the only gauge hooked up to the limiter, is that the ONLY thing it affects? Or would something else be affected by it?

That is the only gauge that uses the limiter as that is the only gauge besides the ammeter... and the ammeter doesn't use the limiter.

 

[Ghostultramarine]

Thank you!

Now, with that 12v to 5v limiter you linked to on eBay, would I then need to use 5amp fuses for the dash lights (as opposed to the 4amp recommendation on the fuse box)?

Or does it use another fuse?

 

[Gerald Morris]

Use 5 amp fuses. I played with that voltage converter myself, and bought 2 of them. They work well enough, but then I bought the Autometer gauge which uses 12V. No need for any 5V stuff on my ride now.... You might avail yourself of that Autometer gauge. It works damned well.