John S Posted January 24, 2015 Share Posted January 24, 2015 Someone please help me out I installed the 3rd gas sending unit that doesn't work 1970 Monte. Let me explain. I tested with ohm meter should read 0-90 ohms it read 0.2 - 90.1 excellent. Next I hooked to the car and grounded unit to where it grounds on the car. I moved the float the full range of travel and the gas gauge read accordingly. All the way down it read E all the way up read just slightly past F. Checked @ 1/4 1/2 & 3/4 and everywhere in between. Gauge read accurately. Put sending unit in tank and checked one more time it read 0.2 ohms then turned tank upside down it read 90.1ohms, good or so I thought. Put tank back in car and put in 2 1/2 5 gal cans of gas, 12 gal, gas gauge read 1/4. Decided to take car for a ride, upon acceleration the gauge would drop a little but only come back up to a little over 1/4. Went to get more gas put in another 7 gallons. By my estimate I now have anywhere between 17 and 19 gallons in tank. Gauge reads just over 1/4 tank I disconnected wire in trunk and checked ohm reading it read 33 ohms so the ohm reading is correct to the gauge reading. Seems like float is not going up, I also checked float in liquid and float "floated". This is an AC Delco sending unit I have been a mechanic for 37 years I am STUMPED. On the bright side I am getting very proficient at R&R of gas tank. I sanded ground connection on car and used a star washer for better contact. Any ideas? I also tested gauge, disconnect wire turn on ign. and gauge goes way past full, ground the wire gauge goes to E. I am 2 steps away from drilling two holes in side of tank and installing a sight glass. I even used our company's borescope to look inside tank to make sure nothing was hanging up and it looked good. This sending unit is kicking my butt. Has anybody experienced this, or have a fix? John S Quote Link to comment Share on other sites More sharing options...
stangeba Posted January 24, 2015 Share Posted January 24, 2015 In all of your testing that yielded good results, where / how is the sending unit wired, both to the gauge and the ground vs when the results are poor? I see you flipped the tank upside down to simulate full so I assume there must have been a longer wire / wires or jumper wires attached to the sending unit. If so, are they in any way receiving a better cleaner connection? So many electrical problems are due to a poor ground, I always look there first and I see you have done that so what is different? Tough one for sure, good luck! Bruce Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 24, 2015 Share Posted January 24, 2015 is the float/arm being obstructed by the filler neck? remember...on a factory tank they extend into the tank almost to the opening for the sending unit I have read here many times how the float arm is incorrect and the float hits the filler neck Quote Link to comment Share on other sites More sharing options...
John S Posted January 24, 2015 Author Share Posted January 24, 2015 I flipped the tank when it was sitting on the bench It was not hooked to the car. All grounds have been cleaned and it worked before unit came in contact with gas then the float does not seem to rise. I will remove sending unit again this time I will do my tests while unit is submerged in gas. Something seems to happen when gas is put into tank Simple electrical hookup One tan wire that connects to stud on sending unit and connects in trunk to wire coming from resistor side of gauge, and one ground wire from body of sending unit to body ground which I did check for good connection. John S Quote Link to comment Share on other sites More sharing options...
John S Posted January 24, 2015 Author Share Posted January 24, 2015 I inspected inside the tank with the borescope camera it is unobstructed and moves freely. Something seems to happen when gas is put in tank. I will get borescope and inspect one more time and will test sending unit when it is immersed in gas and check if float arm is hanging up. After that I'm out of ideas. John S Quote Link to comment Share on other sites More sharing options...
overdrive Posted January 25, 2015 Share Posted January 25, 2015 Make sure the float doesn't have a leak that's letting fuel inside of it. Dan Quote Link to comment Share on other sites More sharing options...
John S Posted January 25, 2015 Author Share Posted January 25, 2015 Put 10 gallons of gas back in tank and put borescope camera into filler neck you can clearly see fuel level 1/2 way up the tank and float is submerged resting on bottom of tank. Going to use coat hangar to jar float to see if it will rise or stay at bottom. if it will rise and float on gas than there is binding in the float arm. If it falls back to bottom then float is bad. John S Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 25, 2015 Share Posted January 25, 2015 are you ready to install your tank with velcro yet? Quote Link to comment Share on other sites More sharing options...
John S Posted January 25, 2015 Author Share Posted January 25, 2015 That would make it easier to R&R Have to R&R again float arm popped up when I bumped it but when I pushed it back down it stayed down Quote Link to comment Share on other sites More sharing options...
John S Posted January 26, 2015 Author Share Posted January 26, 2015 Saturated float and even with new float on for some reason arm binds and will not go past 1/2 way when I immersed it in gas in another container to test it. Guess I will try my luck a fourth time John S Quote Link to comment Share on other sites More sharing options...
stangeba Posted January 26, 2015 Share Posted January 26, 2015 Is this an American made part? Sorry you have had so much trouble. Quote Link to comment Share on other sites More sharing options...
John S Posted January 26, 2015 Author Share Posted January 26, 2015 AC Delco made in Mexico Quote Link to comment Share on other sites More sharing options...
70 Iron Posted January 26, 2015 Share Posted January 26, 2015 John,would you have the GM # for yours,I have a new one for a spare if I would ever need one and was curious if its the same as yours. My sticker on the box reads, GM # 19179531 also ACD # FLS1079 It also has the yellow float Thanks Quote Link to comment Share on other sites More sharing options...
John S Posted January 26, 2015 Author Share Posted January 26, 2015 Mine was ACD FLS1079 the GM part # on the box was 6428035 It had the yellow float. John S Quote Link to comment Share on other sites More sharing options...
70 Iron Posted January 27, 2015 Share Posted January 27, 2015 thanks,the one # is the same,GM# is different . Hope mine will work if ever needed Quote Link to comment Share on other sites More sharing options...
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