Another gas gauge issue

-
supertruck

supertruck

Unretired Old Fart stock car racer
FABO Gold Member
Joined
Feb 14, 2016
Messages
790
Reaction score
457
Location
Gloucester, Va
Trying to button up the dash cluster on my 73 Sport project. I did the MAD bypass, installed a Sun volt gauge in place of the factory amp gauge, and it works. Added aftermarket oil pressure and water temp gauges, tying into the factory wiring for the feeds from the sending units. They work fine. Gas gauge in the dash does not work. Here's what I've done so far:
1 - checked voltage coming into the dash from the red wire at the round plug. Got voltage.
2 - Checked the connector behind the kick panel for the blue wire from the gas sending unit. Got voltage.
3 - checked the blue wire at the dash plug. Got voltage.
4 - had already replaced the IVR with a digital unit. Has voltage and the red indicator light flashes when energized.
5 - checked voltage at the gas gauge connectors. Got voltage.
6 - grounded the plug at the tank and turned ignition on for a short time. Gas gauge went to full immediately. Back to empty when ignition turned off.
Thinking the sending unit was bad, I dropped the tank to check it. With the Ohm meter on the connector pin and grounded against the flange, the Ohm meter reads 8.1 at full and transitions to 76.6 at empty. Do I look at replacing the gauge? Since they're pretty expensive, is there a test I've missed? Sorry for the long post, but I wanted to list all the checks I've done so far.
 
Does gas tank have a good ground when in car? If there is no path to ground for sender it will not work.
 
Yes, the metal ground strip that goes from the fuel outlet tube to the metal fuel line is on there. I also cleaned the connector strip and cleaned where it touches the gas line and the tank outlet. Even added some dielectric grease at those points to be sure I had a good connection.
 
Hey Supertruck,

You said you checked the IVR. The Voltage output should be 5-6 volts. If it is too low, gas gauge will not work. Also, the temp and oil pressure gauge share the 5 -6 volt output from the gas gauge. Try disconnecting the aftermarket gauges from the cluster and see if the gas gauge works. The aftermarket gauges may not work the same as the originals use bi-metallic strip technology to indicate readings. The electronics they use may be interfering with the older technology.
Just a thought , hope it helps!!
 
Thank AAndrews, I'll check it out. For the new water and oil gauges I removed the sender feeds from the dash plug and tied into them separate from the cluster so I don't think they would affect it. But I did not check voltage output of the IVR. I'll check that. I'm also going to recheck the grounding of the tank itself as Mike69cuda suggested. Could be the factory strap is not good enough and I need a hard wired ground. Some good info here.
 
Factory ground straps are usually good enough. I would check voltage output of the IVR, and gage cluster to instrument panel ground.
 
supertruck said:
Thank AAndrews, I'll check it out. For the new water and oil gauges I removed the sender feeds from the dash plug and tied into them separate from the cluster so I don't think they would affect it. But I did not check voltage output of the IVR. I'll check that. I'm also going to recheck the grounding of the tank itself as Mike69cuda suggested. Could be the factory strap is not good enough and I need a hard wired ground. Some good info here.
Click to expand...

All you will need to check this is a piece of wire with alligator clips on each end . Clip one end of the wire to the tank and the other end to the chassis. If its a ground problem, this will eliminate it and you will know thatt the tank is not grounded properly.
 
Thanks guys, I'll be on it tomorrow. Since the cluster is out of the dash, I grounded the IVR to the same bolt I used for the headlight switch ground so I think that's good.
 
The gauge is isolated from ground so ground isn't a factor. Voltage from IVR goes into the gauge at one post, travels approx. 13 inches of 1 ohm per inch insulated resistor wire, then out at the other post. So what happens if the insulation is fried / broken allowing the resistor wire to short to the bimetal beam its wound upon? The entire gauge becomes hot. Since the gauge is isolated from ground the only thing that changed was the approx. 13 ohms resistance from post to post. The resistor wire wouldn't heat up like it should. gauge no workie. No open circuit or short to ground to be found.
 
Found the problem. It was the gas tank ground. I did away with the stock metal clip that connects the sending unit outlet to the fuel line as a ground. Instead, I connected the fuel line outlet from the sending unit directly to a frame ground. Problem solved, the gauge works. Thanks for all the suggestions on here.
 
Might be a dozen clips attaching the hard fuel line to the chassis. No doubt about chassis ground path there when the vehicle was new. Somewhat difficult to believe it would fail completely but... enough resistance to prevent sender function is witnessed. There have been similar threads, fuel gauge comes and goes with weather/rain.
One remaining question... Did you reuse the original seal at senders mounting? I can't say "I know it will leak." Every one I've removed showed enough deformity that I expected it would leak.
 
Thanks Redfish your knowledge is invaluable to all the members here. I did use a new seal when putting everything back together.
 
Well here's something I'm going to stick in my mental tool box so I don't chase my tail later on if that happens to me
 
Redfish, to reply to your comment on the fuel line. When I added the sub frame connectors, I removed the old stock gas line and replaced it with NiCu line to clear the connectors. The line is mounted with rubber isolated clips. That may be the issue with my tank ground. Didn't think of it until your post.
 
You must log in or register to reply here.
-

Back
Top