Gas Gauge Issue - Bit Different Than Most

[LuvNLife]

Ever feel like you're living under a dark cloud? I sure as heck do, with all the issues I've been having recently. Here's the new one.

Stock 305/700R combo in an '87 SWB fleetside. New (less than 20 hours ) POL between-the-rails fuel tank, with new POL sending unit into a Holley red pump. Fuel gauge is a new (less than 10 hours) Summit mounted under the dash.

The sending unit was off about 1/8 tank, which is fine. Today, got my new exhaust installed then did a bunch of errands, and it went from under 3/4 to 1/2, then dipped below 1/2, but above 1/4. I stopped for gas and put in right around 10 gallons, figuring there were about 5-6 still in there. Start it up to drive the last mile home, and notice the gauge is sitting at 1/4. Got home, still at 1/4. Shut if off, turn the key back to On, watched the gauge and it pegged Full, then dropped back to 1/4 again, all in the space of about 1 second. Did this twice more, and same result. I'll be able to get the truck in the air tomorrow, and sure could use some troubleshooting tips on where to begin looking for the problem.

Jerry

[rajincajintj]

from the cheap seats - it sounds like a loose ground

[rich weyand]

The "reads 1/4 when full" problem is usually a busted resistor. It can also revert to normal operation due to temperature change, etc., then go back to 1/4-tank mode. I had one that read 1/4 tank in the winter until the cab heated up, then worked. Worked fine in the summer.

See diagnosis chart here:
http://www.chevyclassicsclub.com/the...ry-1965-newer/

Here is one source for the resistor. I used this one; works fine in my 1978. I don't think it changed from 1965 through at least the end of the squarebodies.
https://www.classicmuscle.com/p-6237...-resistor.aspx

[chengny]

Today, got my new exhaust installed

If this problem didn't exist before the exhaust work was done - and arose immediately after - it might be a good idea to check in that direction. Specifically, that the tank level sensing lead is too close to some part of the new exhaust system and the insulation has melted?

[rajincajintj]

Originally Posted by rich weyand

The "reads 1/4 when full" problem is usually a busted resistor. It can also revert to normal operation due to temperature change, etc., then go back to 1/4-tank mode. I had one that read 1/4 tank in the winter until the cab heated up, then worked. Worked fine in the summer.

See diagnosis chart here:
http://www.chevyclassicsclub.com/the...ry-1965-newer/

Here is one source for the resistor. I used this one; works fine in my 1978. I don't think it changed from 1965 through at least the end of the squarebodies.
https://www.classicmuscle.com/p-6237...-resistor.aspx

wow,

great reference! im bookmarking that one. thanks