Fuel gauge not working-again

[Ifitaintbroke]

 Greatly appreciated, Jim! And I'm praying for your sister.

[Ifitaintbroke]

I tried to email you but of course the forum email isn't working.

[ArdWrknTrk]

If you understand what it means you will be praying that she is at peace in the end.

I will check my spam folder....

[Gary Lewis]

I emailed the two of you.

[ArdWrknTrk]

Got it and replied all.

Bradley, I'll send you my cell, so we can text if need be.
You give me a proper delivery address.

[ArdWrknTrk]

Ironically, I may have had it mis-wired all along!  

This is what happens when you get cocksure.

Anyway, it's out now, and I'm going to enjoy 5/8 is empty and way below empty is full!  🙂







Also, my parking brake switch was bad, so I need to find a new one.  💡

[Gary Lewis]

Bummer!  I've wondered why mine is rock solid and yours isn't.  

[ArdWrknTrk]

Perhaps, because I'm an idiot!?  

[Gary Lewis]

We know that's not true.  But apparently you "accidentally" miswired it?  

[viven44]

Might I guess it was perhaps a case of "confirmation bias"?

[ArdWrknTrk]

I can be quite dense.  

I think I followed convention on the board, and as you see I had 'random' colours of wire.

I will do my best to get to the Post Office on Monday.

Happy Easter, to everyone who celebrates!  🐇🐤🥚

[viven44]

I filled up the bronco all the way today. 3/4 way is all the gauge will read when full. I must have tested the gauge with a 10ohm/73ohm resistor before painting the needle and installing it. I have 2 spare clusters that I could have picked a good fuel gauge from. Oh well, as long as we keep track of miles and we know what is full, and empty, who needs a perfect gauge, right ? Besides you have 2 fuel tanks so you are even more set.

[ArdWrknTrk]

Does empty read right on E?
Because you can adjust them.
There's a little rack & pinion type thing inside.

Could the gauge be accounting for additional resistance in the harness between itself and the sender?

[viven44]

OK that's good to know. I don't remember where empty was, but it appears to be an offset to the left. Didn't know it was adjustable. I will need to use a 10ohm and 73 ohm resistor on the harness at the sender to calibrate the gauge.

[ArdWrknTrk]

You could just ohm out the loop from dashboard ground to gauge wire at the big plug for the cluster.

If you still have a full tank it will tell you exactly what the instrument is seeing.💡

[viven44]

OK I think there's a story. I probed the posts on the sending unit using alligator probes and I measured 16.6ohms, so my understanding is that the tank is close to full, but not really full. Maybe I didn't pump it all the way or perhaps this is just where the sending unit truly reads when full.

I wanted to see how the gauge's calibration is... I like to tie resistors on bolts that are approx. the same diameter as the sending unit posts and insert them into the harness.



Here is 78 ohms on the gauge (68+10ohms)


Here is 13.3 ohms on the gauge (10+3.3ohms)
10 ohms would clearly read full



Here is 16.6 ohms on the gauge (10 + 2*3.3 ohms) --- matches what I exactly saw with the harness on the sending unit



The gauge appears to be more accurate on the empty side (Which is good). I guess 16.6 ohms is a 25% increase over 13.3 ohms so it makes sense that the gauge has dropped a quarter of the way. Clearly, a 3.3ohm difference on the empty side (>70ohms) is much less significant so the gauge's accuracy would be similarly better.

I will need to see how good things are on the empty side as far as sending unit resistance. Maybe I should have figured that out when the gas tank was actually empty

[ArdWrknTrk]

Which, again, means you need to drive it more.

I don't think the senders are truly linear.

Though these two newer tanks are the first time I've had to resort to Bullnose senders.
The "one year wonder" Bricknose mechanical pump senders are unobtainium now.

The original senders in my Bricknose were a little weird below a half tank, until it got down to 1/8 or so.

[viven44]

I love one year wonders! The 1980 I had was a treat to find parts for.

With the sender in the tank now I’m stuck with whatever it is. Adds to the “quirks”.

Hopefully this info is useful in this thread.

[Ifitaintbroke]

I've often wondered how difficult it would be to engineer a sender to be truly accurate. I've decided I'm going to try the reed switch sender from Tanks Inc. I will have to put an extra hole in each tank, but that won't be difficult, as long as I have all the gas fumes out 🔥.

[ArdWrknTrk]

Link?