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Need help with gas gauge
My ERA came as a roller, so the rear harness was factory installed. I have a Smith's electronic gas gauge and SW float type denser in the tank. The gas gauge has never worked. I went through all the trouble shooting in the wiring manual:
- when I ground the sensor wire, the gauge reads full. - with the sensor wire connected, the gauge reads empty, even when the tank is full. Today, I drained and dropped the gas tank, and removed the sensor. On the bench, the sensor gives 25 ohms at empty and 125 ohms at full(float up). I thought the float might be rubbing the front wall of the tank, so I bent the arm a little to make sure it clears. I hooked the sensor to the car, and watched the gauge while I moved the float. It worked perfectly. I put the sensor back into the empty tank, and the resistance was still 25 ohms. I reinstalled the tank, put 5 gallons of gas in it. The gauge will not move. I thought maybe the sensor screw was hitting the underside of the trunk floor, so I checked the resistance with the tank in the car ((still has 5 gallons in it). Got 25 ohms. Does anyone have any ideas? I'm all out of them. Thanks in advance. |
I'm not familiar with your setup but this guide from ERA should help.
Smiths Fuel Gage Troubleshooting |
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I am wondering if 5 gallons is enough to show on the gage. The tank is 19 gallons. I could put another 5 in it, but if I end up having to drain the tank again it is a pain. |
It's possible that 5 gallons might not be enough to register.
I haven't had to work on my ERA's unit, but I've had to fiddle with various tank gage unit over the years to tweak the arm and float where it bottom out just a little off the floor of the tank. Did you look the float over carefully - any chance it's leaking and filling with gas? The tank should be well grounded to the frame but maybe the gage sender is being isolated from the tank by the gasket. As I remember I had only a single wire hookup on the ERA. But I've got an old Plymouth that actually has a ground strap from the sender tube across the rubber connection hose and tied to the steel supply line. I think my Corvette sender may have a separate ground from the sender unit to the frame or harness. Might try connecting a ground wire to the sender unit steel and see if that helps any. |
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I wondered if the cork gasket was keeping it from making a good ground so I checked that. With the screws into the tank, the ground was good according to my multi meter. I wonder if this is the right sender for my gauge. I have the Smith's type 4 (from the Wiring Primer) and it says this gauge needs a 350-40 ohm swing type sender. I pm'd Bob a while back and he said I need the SW sender. So one of them is wrong. I get 125 full -25 empty on my sender. |
When you had the sender out and were checking travel, did you try it connected to the gage? Alligator clip a local ground and run it thru the swing and watch the gage.
This article is the easiest IMO on the swing setup top and bottom of tank. https://www.hotrodhotline.com/instal...uge-and-sender I almost bought one of these gage/sender calibrators, but found my issue was the gage wouldn't return to zero (mind of its own) and purchased a Speedhut programmable gage instead. Classic Instruments Store / SN34 https://www.speedwaymotors.com/Class...ce,230181.html http://www.classicinstruments.com/us...n%20020116.pdf Edit I just re-read you 1st post. -"when I ground the sensor wire, the gauge reads full." When you ground it your giving the gage Zero Ohms. AKA= low OHMs when full, High OHMs when empty. Later you wrote. - "On the bench, the sensor gives 25 ohms at empty and 125 ohms at full(float up). IF so your sender is 180 out from what your gage needs for an input. It is possible to flip the float (loosen the set screw and run the rod thru from the other side) So that down is up per se. Take a look at the article I 1st posted above from hotrodonline. |
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I'll read the article. Thanks for your help. |
A couple of (unlikely) possibilities:
The swing arm was too long, so it's jamming against the bottom or side of the tank. Somehow, the tank is not grounding to the chassis. |
Thanks for the help. I will check all these things in the morning and report back.
Spdbrake - I am sure the sender is not 180 out. When I worked the sender outside the tank the fuel gauge moved in the correct direction. |
I was back at it today. I was more diligent in collecting information than yesterday. With the tank sender removed from the tank, I got:
246 ohms with the float in the empty position 32 ohms with the float in the full position I checked to see if the float leaks. It does not. I checked the range of motion of the float with the tank depth. While doing this, I noticed the float was not horizontal. It turned very easily, from vertical to horizontal and any other position. I tightened the set screw holding the float rod as tight as I could, making sure the float was horizontal. It seemed fairly secure. I then hooked the sender up to the car, still outside the tank, moved the float and watched the fuel gauge. With the float fully up, the fuel gauge reads about 7/8 fuel. In several other positions, the fuel gauge seemed to track the float position fairly well. I put the sensor back into the tank, and checked the resistance between the center screw and the tank. I got 246 ohms, which it should be. I will install the tank back in the car tomorrow and try again. I think the loose float hanging vertical and only 5 gallons in the tank was not enough to make the fuel gauge move. Back tomorrow with the results. |
That sounds mucho better Chris.
Appears you have a 240-33 sender(common aftermarket) I'd check the OHMs reading at the gage while you have the sender at Full (gage showing 7/8) If you have a dirty or loose connection (adds resistance) which could explain the 7/8 reading. (say the gage is seeing 45 ohms at full) |
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Dumb question but you have continuity between the sender and the tank but do you have a good ground between the tank and chassis?
Larry |
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The tank is back in with 10 gallons of fuel, over half a tank. The fuel gauge does not move off of dead empty. I'm out of ideas. It works before I install the tank into the car. Gauge is good, sender is good, wiring is good. Then, with the tank installed, it no longer works. I guess I'll keep using the tripometer as a fuel gauge. But hanks for everyone's suggestions. |
It doesn’t help to jump a wire from the sender directly to chassis ground, does it?
It bypasses the tank that way. Larry |
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Before I installed the tank, I check continuity from the sender to the tank with my meter. It indicated no resistance between the two. |
I cut a hole in my trunk to access the sender (cuz I'm lazy). But I was off a bit in my calculations. 3" is a bit right?
I should have bought one of these. https://walabot.com/diy |
Peter at ERA suggested that. I decided to pull the tank instead. Twice.
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There is a spade connection in the signal wire at the corner of the tank. I started wondering if the tank side of the connection is bad (I know the car side is good). Just checked, it's good.
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Hi Chris.
I had a similar problem recently. If you have fibre or nylon washers on the bolts. The sender does not earth to the tank through the bolts. You need to connect an earth from the chassis directly to the sender unit base. Some sender units have an earth wire spade soldered to the sender unit base. Some don't. The earth wire if connected to the sender base by the bolts. You need the wire/ terminal to have direct contact with the sender base. ie no washers between the wire and the sender base. Hope this helps and you can be out enjoying your ride. Bender |
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