84 k5 Stock fuel Guage stuck on 1/4 tank???

[123jerryeric]

Hello! I need some help! I'm stumped! 84 gmc k5 blazer. Initial issue was tired of my gas guage only reading 1/4 or less. I put a new sending unit that checks out correct on ohm reading correctly (0-90). Also I have good 12v power to guage. both solid grounds and my pink wire running from sending unit to guage seems to look good. Guage itself checked correctly too (pegging over full when removing sending wire) and shows 90 ohms on multi meter when checking guage by itself. both my old fuel and new sending unit reading good but both only read 1/4 tank on guage.and all good power and grounds and I still CAN NOT get it to read over 1/4 tank no matter what!! Seems all the stuff is checking out like it's supposed to. What is my issue??

 

[123jerryeric]

This is the initial forum I been looking at but I can't find it again to reply on it

 

[77Dmax]

Does it peg to empty if you ground the sender wire? Thats more important than going to full unplugged..

 

[123jerryeric]

I just went out and double checked. If I take groun wire loose from sending unit to frame it still reads 1/4. If I take the red wire off fuel sending unit it pegs full. So even with ground wire not attached to sending unit it still reading 1/4. Even if I move it with my finger it goes right back to 1/4 even with that one ground completely off
.
If I keep ground hooked up, and ground out the sender wire it does drop to E. Put sending wire back on the post and right back to 1/4 tank.

 

[77Dmax]

Ground the sending unit wire itself.

 

[123jerryeric]

If I keep ground hooked up, and ground out the sender wire it does drop to E. Put sending wire back on the post and right back to 1/4 tank. OH YEAH! And According to how much gas I seen in it (3/4 tank) when i had sending unit out and what the sending unit reads in ohms ( about 65ohm) which means right at about 3/4 tank also. So I know for a fact there is well over 1/4 tank of fuel in the tank as I'm doing all this testing. I've watched countless YouTube videos of the whole system and I can not figure it out.

 

[77Dmax]

Check the ground on the gauge itself.

 

[123jerryeric]

I have ran a separate ground wire to it to triple check the ground on guage to dash.... isn't it odd it still reads 1/4 even when ground from tank is disconnected?

 

[Jgonick]

Sounds like a gauge problem (If I read everything correctly) Did you double check the nuts on the gauge terminals to make sure they are not loose? Also check ground on gauge (@77Dmax mentioned) There is a resistor on the back of the gauge that might be going bad. The new gauges have the resistor internally.

 

[123jerryeric]

I actually took the resistor off the back of the guage and cleaned it nice and well. And guage reads 90ohms when tested alone should mean resistor is good right?, it pegs full when sending wire is disconnected. That all signs of a solid guage right?

 

[Jgonick]

B=battery S=goes to sender G=ground

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I found this a while back_ haven't checked it personally, but it looked correct.

 

[123jerryeric]

Im pretty sure i have good ground and power on cluster and guage. Should I try it with out resistor? Or maybe just try to install a aftermarket universal guage with everything built in?

 

[77Dmax]

Have you run a new ground to the tank/sender?

 

[77Dmax]

Actually you might check the engine/body ground as well.

 

[123jerryeric]

The new sending unit (even tho old one was fine) came with entire new ground wire crimped on. I cleaned frame well when attaching. Shows I get good ground there too when I test sending unit with ohm and test light. And every thing else in truck and dash works well, should I still check engine to body ground?