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| Gas Gauge Problem https://slantsix.org/forum/viewtopic.php?t=33675 |
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| Author: | Family Scamp [ Sat Feb 07, 2009 8:58 pm ] |
| Post subject: | Gas Gauge Problem |
Ok I give up and need your help on a gas gauge problem. I will review my problem and what I’ve done so far. Car: 1973 Plymouth Scamp 6cyl 225, 16 gallon gas tank sending unit new 1yr ago. Problem: Gas gauge reads full when tank is full and then drops quickly to half then a quarter. When tank is re-filled only 4 – 6 gallons are need in this 16 gallon tank. Temp Gauge works fine. What I’ve done: • Checked Ground at tank to sending unit, it’s good. • Removed Instrument Cluster: o Circuit board looks good and continuity good on all connections. o Regulator tested ok but I replaced with a solid state constant 5volt type. • If I grounding lead at tank it sends gas gauge at dash to full. • Ohm meter at sending unit reads 48 ohms which by my estimate is about half full which the tank should be based on when I filled it last. • Ohm reading at dash connection reads ~47 ohm so no wire issues from tank to dash. o Tested Gas Gauge at tank by connecting 9v battery to + side of gauge – side of battery to car ground then – side of gauge to sending unit, gas gauge only reads quarter full it should read half based on ohm reading of 48. • Gas gauge continuity across leads tested OK at 12 ohms. • I decided to replace Gas Gauge anyway. (check out http://www.cjmotorparts.com great selection of NOS parts) o New NOS gauge reads the same as my original gauge. Ok so I’m left with the sending unit being faulty. I purchased it a year ago but the folks at Quanta Products ( http://www.quantaproducts.com) will replace it if I think it is faulty. This problem shouldn’t be this hard to figure out but I may be missing something obvious any suggestions? Should I swap out the sending unit? Thanks as always for your help. |
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| Author: | Pierre [ Sat Feb 07, 2009 11:48 pm ] |
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Has it always been like this for the year after you replaced the sending unit? I've had bad luck with aftermarket sending units. My original one was working fine. I kept that one aside and replaced it with a "new" one as I wanted to add an EFI return line and didn't want to do anything to the original. I went through I believe 3 different units of 2 different brands, and none read the same resistance at the same levels as the original. I've read several stories of the same tale on moparts. All the aftermarket (and even mopar replacement) ones I've seen have a short float arm with the pivot point a few inches down the pipe. My original had a long arm, and the pivot was at the base circular plate that mounts it to the tank. I don't think I've seen an aftermarket one like that. |
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| Author: | Family Scamp [ Sun Feb 08, 2009 8:23 am ] |
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Hi thanks for the reply. Yes the readings at the gas gauge has always shown low right from the install of the new sending unit. Also I think I checked the resistance on the new sending unit before installing by moving the float arm up and down and checking with my ohm meter. Thanks for the tip on after market sending units and possible different arm lengths etc. |
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| Author: | stonethk [ Sun Feb 08, 2009 8:27 am ] |
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Another possibility. I had this problem on a truck of mine. The float in the tank sending unit was filling up with gas. When the tank was full it registered as such, but as the gas entered the float it would sink giving low fuel reading at the gauge. |
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| Author: | Pierre [ Sun Feb 08, 2009 9:08 am ] |
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Hopefully thats the case with the original poster, but not with mine. I used a new float that came with the sending units, and tested it for leaks by dunking it under water - no bubbles. The resistance is just calibrated differently, theres no way getting around it. Check out the experiment I did here. I'm sure you could devise your own similar experiment using gas or even doing it dry by fashioning something to move the arms at the same level. |
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| Author: | 65Dodge100 [ Sun Feb 08, 2009 10:49 am ] |
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| Author: | Family Scamp [ Sun Feb 08, 2009 5:59 pm ] |
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Thanks for the additional information. The links sent were very helpful. It looks like my next step should be to pull out the sending unit and look for a damaged float and then play with the adjustments etc to calibrate this to my dash gauge. I know how to remove the sending unit but does anyone know how empty the tank should be so I don't get a flood of gas on me when I remove the sending unit? |
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| Author: | 65Dodge100 [ Fri Feb 13, 2009 4:05 pm ] |
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Sorry, I've never taken a tank out of one of those. Though, I'd try to get most of the gas out just to save weight and make the tank easier to handle. Danny |
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| Author: | Family Scamp [ Sun Feb 22, 2009 4:55 pm ] |
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An update on my gas gauge problem. I removed the sending unit and the float, a plastic one, had a small amount or gas in it. So I think this solves the problem of reading low, the float was sinking. I received the new sending unit and I checked it out thoroughly taking ohm readings at the sender and the gauge before install and it all checked out. Happy I had found the problem I re-installed the instrument panel and installed the sender. Guess what? The half full tank still reads between E & 1/4. I am convinced now the "relationship" between the tank and the position of the float is off. I will not put this on the road until late May when I'll do some more testing. thanks everyone for all the help and advice. |
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| Author: | Family Scamp [ Sat Feb 28, 2009 8:58 am ] |
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To update: The new sending unit arrived so I removed the old one. There was gas in the float so that was pulling the arm down giving me a lower than actual reading on my gas gauge. • Before installing the new sending unit I thoroughly checked it out with my ohm meter, it checked out fine. • I then attached to the connection at the tank and moved the float arm up and down and got similar ohm readings at the connection on the instrument cluster, so my wire and ground are good. • I then installed the instrument cluster and again attached the new sending unit to the connection at the tank and moved the float arm up and down and the gauge in the dash worked fine. • I installed the new sending unit into a half tank of gas and guess what? It reads between E and one quarter full. I am wondering could the arm need to be bent? I wonder if the relationship between the float arm and the tank is off. I called Quanta, they said no it all should match. So at this point I’ll wait to May when I put this on the road run it dry and then fill it at a gas tank and watch the gauge. Thanks everyone for you help and advice. |
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| Author: | 65Dodge100 [ Sat Feb 28, 2009 2:18 pm ] |
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| Author: | jbc528 [ Sat Mar 07, 2009 5:56 am ] |
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| Author: | Family Scamp [ Sat Mar 07, 2009 2:09 pm ] |
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Thanks for the float adjusting advice. I'll try it. I supposed another less elegant way to do this would be to run the tank dry. Put in 2 gallons of gas, pop out the sender and adjust the float until I get a reading of E. This way I'll have enough, I get about 12 -14 MPG to find a gas station. The car goes on the road when this snow leaves us and I'll work on it then. |
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| Author: | 65Dodge100 [ Sat Mar 07, 2009 6:38 pm ] |
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Quote: I supposed another less elegant way to do this would be to run the tank dry. Put in 2 gallons of gas, pop out the sender and adjust the float until I get a reading of E.
That might even be more accurate if you can check it each time with the tank in place and the car on level ground. Danny |
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