As long as I have the 50 chevy jacked up to work on pinion angle thought I would take a look at the tank sending unit, (new sending unit and tank in car) when I bought it but no gauge. So I put a GM 0-90 ohms gauge in while installing the new harness. The gauge reads full and the take is close to empty. I checked the resistance on the sending wire and it was .3 which seemed right. Went on to check ground on sending unit, but there is no ground terminal on the unit, just the 5 screws holding the unit in the tank and the center terminal that the sending wire connects to. So wondering if the tank grounds the unit or this type doesn't need a ground, and one have a information on this?
should have a ground wire, probably under one of those 5 screws. Reading full means there is an open circuit somewhere, either it's on the ground side, or the sender wire side. Or the sender is defective. Did you measure the resistance from the sender terminal, to the sender housing? Did you put a 0-90 ohm sender in the tank also? original was 0-30 ohm.
Did you measure the resistance when the sender is in the full position to verify it is a 0-90. There are half a dozen or so different resistance range senders out there. But as squirrel said, it is probably a bag ground.
I had the same problem with a set of v-three gauges only it was reading backwards took float out turned it around on mounting flange works good now, you said it was empty try adding gas and see if it goes towards empty. you are also going to have to add a grnd wire to one of the five mtng screws hope this helps Tom
Thomas, I have two '51 Chevys, one is an original, neither one had a factory ground wire ...... but, when replacing tanks, as an extra measure, I did add a ground wire from a sending unit screw over to a cleaned spot on the frame. A pinched or grounded wire between dash unit and tank unit will show as "empty", on the dash unit. A break in the wire from the dash unit to the tank unit will show as "full" on the dash unit.
Not sure what sending unit is in it, was in when I bought the car just know it is new gas tank, sending unit and pump. I went by the instruction that came with the gauge I installed., said to disconnect the wire from gauge and check resistance between sending unit and ground, I disconnected the sending wire at the gauge and tested the wire which is connected to sending unit and ground came up with 00.3, so I ***umed it was right being there's about 2 or 3 gallons in tank. I think I will try ground to one of the mounting screws first, if that doesn't fix then look into what studebaker46 or 55 dodgec3 suggested.
The new tank I put in my 47 Ford required there to be a ground wire from one of the 5 screws that hold the sender in the tank. If you don't have any other ground for the tank that you can see that may be the issue.
When I bought my last car, the fuel guage did not read correctly and the needle moved backwards. I have two saddle tanks, so needed to make sure both tanks had the same senders, before tackling the guage. I measured the resistance at the guage from empty to full at 1 gallon increments, for both tanks and determined they were close enough. One was 255 ohms empty and about 46 ohms full, the other was 262 Ohms empty and 52.5 ohms full. This did not neatly match the standard listed ranges, so it was unlikely that I could find a guage that matched exactly, and I did not want to drop both tanks and change both senders. I decided to purchase a Cl***ic Instruments fuel link module which allowed me to match the sensors to the guage. You can set where the needle sits for Empty, half, full etc and it automatically reverses the needle direction as required. This will allow me to use whatever guage set I like in the future, as it is easy to re-program. I ended up buying large resister packs (matching the empty and full resistances) so that I could use these to set the guage without emptying and refilling the tanks. If you decide to use this module, check various suppliers, as some list them cheaper than others.
Take the sending unit out of the tank hook up the wires and clip a ground wire to it. Work it manually and have someone watch the gauge that way you do have to add gas until you know if its working. you can then make adjustments to the float arm. you may have to bend it to match the tank depth. Don't forget to turn the key on when you are checking.
If the sender shows 0.3 ohms when it has a few gallons in it, it's not quite right...it could just have a bent arm, or it could be shorted. But either way, it should be reading "empty" at the gauge. Spend some time with the ohm meter, see if you can figure out where the missing wiring connection is between the sender and the gauge (both on the sender wire, and the ground circuit)
I maybe thinking wrong but with a 0-90 unit won't it be at 000 ohm's at empty, so with 2 or 3 gallons in the tank 0.3 should be close. The sending wire from gauge back to with-in 3 ft of tank is new from harness kit I installed. there was 3 ft of wire on the sending unit from when it was installed.
Most sites list pre 64 as 0-30 ohms, post 64 0-90. 0 ohms empty. You will really need to measure resistance empty, full and half full, to get a sense for what guage you need. Take the measurements at the tank with the sender wire disconnected. Then check again at the dash to see if they are close (should be). This should also allow you to determine if you have a problem with the wire to the tank.
Tested gauge by un-hooking sender wire from gauge and jumping ground to it gauge sending terminal went from full to empty, so gauge is ok, then tested sending wire un-hooked running from gauge to sender, showed 000 ohms, so it also should be good. Check ohms on sending unit with wire unhooked, good ground, 00.2, don't know if right if 0-90 unit, so looks like problem is sending unit. Also forgot to mention I connected a ground wire to one of the sending unit tank mounting screws and ran to good ground, didn't make any difference on gauge still pegged past full.
Mmmm. So, if I am understanding you correctly, when the guage is hooked to the sender it reads full. When the sender wire is attached to ground (0 ohms) it reads empty, as it should. This likely means you have 90 ohms or greater through the sender. Can you check the range on the ohm meter - you should have it switched to the lowest scale you can get a reading without it showing open circuit.
000 might mean infinity (open circuit) on your meter. And it should show about 5 to 10 ohms with a few gallons of gas in the tank. Please excuse the spelling. I posted this with my phone.
If you have tested the guage, tested the wire from the guage to the sender, you can't have less than the guage's full scale ohms through the sender. It must be 90 ohms or greater. What does your meter read when it is disconnected. Perhaps you could see what voltage you have at the sensor end of the cable disconnected and then connected. If it's the same, your sensor is open circuit.
Just did another test with meter set at 20, at the sending unit with wire connected I had 25ohm's. At the gauge with wire disconnected also 25, but when I hook wire to gauge sending terminal it registers 00.6 with key off, turn key on it won't read anything.
Are you sure you have your meter switched to ohms? My meter has ohm ranges 200, 2k, 20k, 200k and 2m. Your meter should not read above the range you selected, it should read the same as if it was not connected. I would also not measure resistance with the power on.
Don't if its what you meant, but I did voltage test between ground and sending wire connected to gauge read 6.4 then at the sending unit same reading 6.4. I did check voltage(power wire) to the gauge read 12.6
I think I had meter set wrong, the lowest setting on mine ohm's is 200. When I test on that setting at the sending unit I get 60 ohms. I pretty sure the tank only has 2 -3 gallons in it. If it is a 0-90 ohm sending unit it shouldn't test that high with what gas in the tank. My gauge I bought and installed so I know its 0-90 but the sending was in the car, I think its the wrong one.
Ok! Now we are getting somewhere. I would now add 1 gallon at a time and record the resistance for each gallon until it is full. Then we can work out whether your sensor is set correctly and hopefully what resistance you have at full.
If the ohm's keep going up as they should from 60 that would mean it will be well over 90, so I will have to replace the gauge which 0-90 or sending unit to be compatible
Sure, or get the module I suggested earlier. Adding fuel 1 gallon at a time will tell you how far out your sender is. If the ohms keep going up until full the fuel module can adjust for it. If the ohms stop going up well before full you will have to remove sender and adjust it for your tank.
I guess I didn't catch the part about the fuel module, installs where? Another thing it a 50 chevy but the tank, sending unit is all new so I don't think it would fall into the pre 64.
I think just work out what you have, then work out a way forward from there. Until you know what sender you have and if it is calibrated correctly to your tank you won't know what you need.
Agreed, I don't want to fill the tank this time of year in north Minnesota, 4 months until road time. Luckily I still have contact with the prier owner, and will contact to see if he knows what sender install with the take and go from there thank you and everyone else for helpful information.
***uming you are using a steel tank and not aluminum, I don't know if this means anything to you, but I hope you can read this photo. ....STEP # 8....I found it in my Gauge booklet. It's for a 0-90 ohms fuel sending unit. View attachment 3432648 sending unit.
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