emunder Posted March 22 Share Posted March 22 Yesterday I dropped my gas tank. Had a new tank and sending unit that's been sitting in boxes for a while now. Once it was all installed I put about 3.5 gallons of gas I had in the shop and put it in to get me to the gas station. When I was done and cranked the truck the gauge was still sitting at dead empty. Not gonna lie, I was super frustrated. I knew the wiring was correct because the electric fuel pump was working. Figured I'd go fill it up in case the float was stuck or not reading the small amount of gas I had in there or, worse-case scenario...run out the tank and pull it back out to re-check everything. Leaving the gas station the needle just started working it's way up real slow. By the time I got back in the shop at my house it was reading all the way full. Anyone else have issues with these sending units being finicky? Link to comment Share on other sites More sharing options...
CRittaler Posted March 22 Share Posted March 22 I replaced both pumps and sending units in mine. I had to adjust the float positions on both senders to have them read mostly right. Mine both swing to almost full and are on E with 5 gallons left. They're finicky and I got tired of dropping the tanks so close enough for me. Link to comment Share on other sites More sharing options...
emunder Posted March 23 Author Share Posted March 23 I replaced both pumps and sending units in mine. I had to adjust the float positions on both senders to have them read mostly right. Mine both swing to almost full and are on E with 5 gallons left. They're finicky and I got tired of dropping the tanks so close enough for me. Ok thx bud, appreciate it! Link to comment Share on other sites More sharing options...
viven44 Posted March 23 Share Posted March 23 Ok thx bud, appreciate it! Do you have a 5 pin fuel selector switch ? If you do then on your truck, the sending unit's resistance value goes through the selector switch. If the selector switch has a high resistance it will make it look like the fuel tank is empty. After a while the switch may settle causing the sending unit's resistance to be sent through. You can either replace that switch or open it up and fix it. Here is my video that talks about it a bit Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 23 Share Posted March 23 Do you have a 5 pin fuel selector switch ? If you do then on your truck, the sending unit's resistance value goes through the selector switch. If the selector switch has a high resistance it will make it look like the fuel tank is empty. After a while the switch may settle causing the sending unit's resistance to be sent through. You can either replace that switch or open it up and fix it. Here is my video that talks about it a bit This is not true. The selector switch should have negligible resistance. Resistance comes from the sender. The gauges work by heating up a bimetallic spring, just like a choke cap. This damps movement, preventing wild swings from gas sloshing around.in the tank. Hysteresis is built into the gauge itself, because it can't heat or cool instantly from the tiny power it gets from the ICVR. Edit: response, to a deleted post.... Link to comment Share on other sites More sharing options...
viven44 Posted March 23 Share Posted March 23 This is not true. The selector switch should have negligible resistance. Resistance comes from the sender. The gauges work by heating up a bimetallic spring, just like a choke cap. This damps movement, preventing wild swings from gas sloshing around.in the tank. Hysteresis is built into the gauge itself, because it can't heat or cool instantly from the tiny power it gets from the ICVR. Edit: response, to a deleted post.... Yes the selector switch has negligible resistance but as the switch ages, it will develop resistance and that will prevent the sending unit resistance value to reach the gauge. In the picture below the link in the circle, when that has a high resistance it will completely overwhelm any sending unit resistance. Worse case if the switch is fully open, the sending unit is pretty much useless Edit: I deleted because I wanted to double check the wiring diagram. I am sure of it now!! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 23 Share Posted March 23 Yes the selector switch has negligible resistance but as the switch ages, it will develop resistance and that will prevent the sending unit resistance value to reach the gauge. In the picture below the link in the circle, when that has a high resistance it will completely overwhelm any sending unit resistance. Worse case if the switch is fully open, the sending unit is pretty much useless Edit: I deleted because I wanted to double check the wiring diagram. I am sure of it now!! My truck is 37 years old and I don't see that my switch makes the readings bad when I test with a meter. But I have old senders and a new style cluster, so my gauges read backwards and I run out when they reach up to 5/8 on the dash. Metermatch is useless for me.😖 I'd rather have some indication than none at all. Link to comment Share on other sites More sharing options...
viven44 Posted March 23 Share Posted March 23 My truck is 37 years old and I don't see that my switch makes the readings bad when I test with a meter. But I have old senders and a new style cluster, so my gauges read backwards and I run out when they reach up to 5/8 on the dash. Metermatch is useless for me.😖 I'd rather have some indication than none at all. Down here in the dust bowl area, we have those switches full of junk when I open them up. I opened and fixed the 78 Bronco's tailgate switch the other day. It was reading about 80 ohms in the down position. No wonder the window wouldn't go down. After I wire brushed the internal contacts, everything was honky dory I think in your 87 truck's switch, the sending unit is hooked up to the gauge through the selector valve right ? As long as the switch commands the selector valve properly it should be good. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 23 Share Posted March 23 Down here in the dust bowl area, we have those switches full of junk when I open them up. I opened and fixed the 78 Bronco's tailgate switch the other day. It was reading about 80 ohms in the down position. No wonder the window wouldn't go down. After I wire brushed the internal contacts, everything was honky dory I think in your 87 truck's switch, the sending unit is hooked up to the gauge through the selector valve right ? As long as the switch commands the selector valve properly it should be good. I don't have Hot Fuel Handling, or an electric pump, but I do believe that my 6-port valve switches senders. I'll have to find my EVTM as it's supposed to continue raining at least into Sunday. Link to comment Share on other sites More sharing options...
emunder Posted March 23 Author Share Posted March 23 Are y’all talking about the tank selector switch? If so mine is a single tank. Link to comment Share on other sites More sharing options...
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