Fuel send unit and gauge issue

[Jay Bee]

I made a couple YouTube videos using my buddy's A-body sending unit. They (1) show how flakey the ground is without the mod and (2) one showing how stable it is with the added wire. I'll post links tomorrow.

[Jay Bee]

@Mrbill426  Here's those videos, no harm in giving this a shot on your sending unit. Just make sure it doesn't interfere with the arm's movement.

First video - without mod & with temporary jumper wire.

Second video - wire mod soldered on.

[Mrbill426]

@Jay Bee thanks for the information and videos    I will be making that mod.
Looks like in order to do that I need to take it back out of the tank which means unless someone has a "trick" the left muffler, tip, and heat shield need to come off.

@Mrbill426  Here's those videos, no harm in giving this a shot on your sending unit. Just make sure it doesn't interfere with the arm's movement.

First video - without mod & with temporary jumper wire.

Second video - wire mod soldered on.

[70rag383]

@Jay Bee  Those are videos are very helpful.  I have a different problem my sending unit. When I fill up the car the gauge reads on F as it should. However when I drive just a few miles the gauge goes down very quickly. When I'm on E the tank actually has half a tank of fuel.  Have you run into this problem before?

[Huskidrive]

I had the same issue with three different repop sending units. I still had my original sending unit.I soaked it in lacquer thinner and replaced the filter sock.  I installed it and it works flawlessly. There is a add on unit out there that you can use to "dial in" the proper readings. This problem has been discussed forever on this forum.....use the search feature it has all your answers.

This old post may answer your problem: Initially I was thinking that the problem was due to the gauge not being calibrated to the new sending unit. It made sense to me that the resistance of the rheostat in the new sending units would be different than factory. So I reasoned that if you calibrated the gauge to the new sending unit, you should regain your accuracy. Unfortunately the issue is a bit more complex.

The original sending units resistance was non-linear. As the float moved from empty to full, the resistance increased more logarithmically. If you graph it, it is a curve. The aftermarket units have a completely linear resistance. Straight line resistance through the entire range of motion. So naturally, you are never going to get an accurate reading with those differences.

Thomas said that what he can do is calibrate your gauge to the min and max resistance values on your sending unit. This will give you accuracy at full and empty. The gauge will not be accurate once you come off of full, but as the float moves down the accuracy will increase until you reach empty where the gauge will accurately let you know that you need fuel.

This is acceptable to me. Since your gauge won't be off the scale on the high end, which looks crappy and by the time it is showing 1/4 tank, it will be fairly accurate. If you like walking, when it says E, you'll be walking.

[Jay Bee]

@70rag383  I've had more than my fair share of sending unit issues from the internal contact arm falling off, to another one that just lost its contact point and lastly, to the float taking on fuel inside it. FYI, those were OEM ones.

IIRC the time the float took on fuel it showed up like something similar to what you're talking about. Shortly after driving, my almost full tank showed a lot less fuel. I thought, "no way is my fuel consumption that bad". Not being an expert in Archimedes' Principles of Buoyancy I thought if the float had a hole wouldn't it fill & drop to the bottom. Well after all else failed I popped the sending unit and sure enough there was a bit of gas inside the float. My guess is once the tank's level dropped some, the heavier float dropped more than usual creating the impression of terrible fuel economy. Anyway, seems like you're going to have to remove yours and investigate. Good Luck.

PS: The picture is just to show some of the things I encountered.

[Mrbill426]

Guess I am really going to need to get that sender out and work on it.  I just put enough fuel in my tank to be darned near full and the gauge still reads less than a quarter tank 

[Jay Bee]

Yup, sure sounds like it. Please keep us informed with what you find. 

[Mrbill426]

It will be a while but I will.  Thanks.

Yup, sure sounds like it. Please keep us informed with what you find.

[Dakota]

One non-electrical item to check if you end up pulling the sender is to make sure that the float doesn't have a hole in it. The one that was in my car when I bought was badly corroded.  A leaking float may not cover all your symptoms but it's easy enough to check by dunking it some gas and see if you get any bubbles coming out if not. 

[Mrbill426]

Thanks I will check that.  Everything is brand new and this is the first time I have put fuel in it.  I would hope the float "floats" but stranger things have happened.

One non-electrical item to check if you end up pulling the sender is to make sure that the float doesn't have a hole in it. The one that was in my car when I bought was badly corroded corroded.  A leaking float may not cover all your symptoms but it's easy enough to check by dunking it some gas and see if you get any bubbles coming out if not.

[Jay Bee]

Yeah, I kind of alluded to that in my Reply#20, but if everything is new that would be pretty odd. Not impossible, just odd.

[HP_Cuda]

Here is a strange one for ya. I had the exact same issues as described earlier in this post. My gauge (brand new) would never read beyond 1/2 tank and it definitely went down non-linearly.

Now fast forward to about 9 months ago, for some reason it started working as it should! I think it had some kink in the wire and ball which prevented it from moving to it's full possible motion. I think I either went over a huge dip in the road or after I filled the tank full again it righted the problem.

Sometimes the problem is mechanical and not electrical. Either way it would be great if there was a vendor that did much better QA checks before sending these out. I would have definitely bought a more expensive unit if I knew it had a much greater chance of success!

[Dakota]

Yeah, I kind of alluded to that in my Reply#20, but if everything is new that would be pretty odd. Not impossible, just odd.

Yep - sorry I missed that. 

[Aloha Randy]

I have and had 2 of the very same issues that you all talk about. Full is good, first couple of gallons drops to just above half tank. A few gallons later drops to empty with about half a tank in place. Two new senders.....