Issues with New Fuel Sending Unit

[Ol'Blue]

Installed a new BC sending unit in an older BC 23 Gal tank. On first fill up the gauge took 10 minutes to slowly greep up to full. Gauge moved down as I went through the tank but when it registered empty, I was still able to go another 75 miles.

The stock tank and sending unit worked fine.

As a test, I intercepted the wires (ground/hot) near the tank and hooked up my old sending unit and it registers correctly and responded quickly to empty/half/full.

I was able to reach in and ground the new sending unit and it jumped up to full right away.

Before I pull the tank, is there any other test I can do or should I just fill it up again and hope it registers correctly on the next fill up?

Thanks,

 

[Viperwolf1]

What is the resistance and fuel level?

 

[Ol'Blue]

I checked the sending unit before I installed it and got = Empty .07 and full .01 when moving the float by hand. I get the same on my old sending unit that was working when I removed it.

Electrical is not my thing and hope I was using the meter correctly.

 

[Ol'Blue]

I was doing some reading and found this - post #14

http://classicbroncos.com/forums/showthread.php?t=256565&highlight=fuel+sending+unit+test

Maybe I just have to live with it this way?

 

[Viperwolf1]

I checked the sending unit before I installed it and got = Empty .07 and full .01 when moving the float by hand. I get the same on my old sending unit that was working when I removed it.

Electrical is not my thing and hope I was using the meter correctly.

Those measurements don't look like they make any sense to me. Need more practice with the ohmmeter.

 

[Ol'Blue]

Those measurements don't look like they make any sense to me. Need more practice with the ohmmeter.

I checked the instructions and practice some more.....with the meter set at 200, I get about 70.4 empty and 11.2 full.

I spoke to BC this morning and they think I have a poor ground which could contribute to the slow reaction in the gauge and the float is not set at the right depth and thats why Im seeing empty when I still have fuel.

Going to pull the tank and sending unit again and reset everything and test everything while the tank is out.

 

[Viperwolf1]

I checked the instructions and practice some more.....with the meter set at 200, I get about 70.4 empty and 11.2 full.

I spoke to BC this morning and they think I have a poor ground which could contribute to the slow reaction in the gauge and the float is not set at the right depth and thats why Im seeing empty when I still have fuel.

Going to pull the tank and sending unit again and reset everything and test everything while the tank is out.

Sounds like a good plan.

 

[70Sport]

I'd like to hear what you come up with.

I too have an older BC tank and just did the same thing, new sender, hoping the fuel gauge would finally be more accurate. No such luck. Gauge is still way off.

 

[DirtDonk]

As a comparison, when the low-fuel light comes on in my Buick, I have well over 100 miles left before it sucks air. Been to 100+ and have yet to suck air, but even then, when I fill it up I come up short of the rated capacity by at least 2 gallons!
So that's a grandpa car and is likely that way to keep ole gramps from running out of gas on the way to play bingo.
In a Regal (even the supercharged one) that's about 3 gallons out of 17. That same 75 miles in an EB is probably like 8 gallons left, and about a third of a tank!

As for the aftermarket Bronco tanks, how are you guys orienting the sending units and how deep do you adjust them? Do you check for depth, making sure the float is near the bottom when it's empty? How long is the arm? And are there stops that can be adjusted?

Just asking questions since I don't know of any exact science regarding that, but know that it might be important.
I know that whether the float arm faces sideways, at an angle, or front-to-back "should" not matter, especially since it's all inside the baffle chamber. It's all just reading the height of the fuel in the tank. But maybe it's angle can help? Or the length of the float arm?
The depth and stroke are key aspects I'm sure.

With the odd shape of the tank and it's taper towards the bottom, a linear reading sending unit is going to always run to empty quicker after it reaches just below the half-way point I would think. That's where the taper has a greater effect on the actual amount of fuel left in the tank per inch of depth.

A setting with a shorter arm might not allow the float to be at the upper level of the fuel when full. Which would explain a lot of the complaints about the gauge staying on full until a LOT of fuel had been used, then a too-quick trip to empty.

Wish I had time to experiment with one when I was at the shop. Would love to put in 1 gallon (probably just of water) at a time to measure the actual depth of liquid in the tank, then compare those numbers to where the float sits, to where the gauge reads.

Anybody have theirs apart and want to experiment? Is none of that worth the time, and is not pertinent to the discussion? Seems like some little things could make a difference. My old NWMP tank never had any issues with the gauge, but my factory sending units had to be tweaked because they never read correctly right from the factory. Always low by 1/4 tank.

Paul

 

[pbwcr]

The float arm has to be bench adjusted before install. Measure the tank then bend the arm to simulate the depth of the tank. Yup, I did not do it and sure enough I have the same issue. Now I have to drop the tank and get it correct.
The reason for the problem is the new tank has a different depth than stock.

 

[blubuckaroo]

I have an Aero tank but I believe the way the sending unit works is the same. The float that came with my tank had an arm that was too short. The float couldn't possibly be adjusted to reach all the way to the top and still swing all the way to the bottom. I made a call to Aero and they sent me a sending unit with a longer arm.
Something you may want to look into.

 

[Ol'Blue]

Ok, I think I got it adjusted as good as its going to get. Once the gauge read empty I was able to go 25 miles before sputtering out of gas which is right about where I want it.

Here's what I ended up doing. I dropped the tank "again" and calibrated the sending unit as suggested by bending the arm on the float.

The sending units range takes to it to full, but at empty was still about 2"-3" from the bottom. I held the sender up against the side of the tank and bent the arm down so it was about 1/2" - 3/4" off the bottom.

To test the slow response I hooked it up to the gauge and ran the sender up and down to see if I had good response at the gauge. The gauge was a little slow to respond but not as bad as the first fill up. To double check, I installed a jumper and went directly from the sender to the gauge and also added another ground. Still slow but not like the first fill up. I also tested my old sending unit and still a little slow but much better. I figured when I first installed it I must not have had a good poss, ground or the float was coming in contact with one of the baffles. Hooked it back up to the original wiring and acted the same as the jumper.

To some of Paul's comments:

The sender is orientated front to back and definitely does not take the tapered tank into account. I set the float at empty, 1/4, 1/2, 3/4 and full making a mark on the shaft at each reading. My marks were consistent with the range of empty to 1/2 and 1/2 to full, but distances between 1/4 and 3/4 were grouped closer together.

Like this:

Empty ---------- 1/4 --- 1/2 --- 3/4 ---------- Full

Hope this makes sense.

I adjust the float to 1/2"-3/4" off the bottom figuring that would give me about 2-3 gallons = to 16-24 miles. I didn't add fuel or water to check, I just estimated.

You cant change the orientation of the float as it will hit the baffles in the particular tank or the back of the tank. I did notice though, if you tighten the positive terminal and you are not careful it will turn the shaft and float causing the float to catch on the baffles. This may have been the cause of the very slow gauge response the first time I installed it.

I hope this helps others.

Thanks,

 

[DirtDonk]

Definitely going to help. Thanks

Now all we have to do to have ultimate tank knowledge is take into account the actual gallonage vs height based on the tapered shape of the tank.;D
Heck, we should just design a tank like some motorcycles and small utility engines, with a clear panel in the tank (gas gawker?%)) with nice graduations!
Now that's a tank I'd like to have in mine. A backup for a failed gauge.

Paul

 

[patterdale]

Definitely going to help. Thanks

Now all we have to do to have ultimate tank knowledge is take into account the actual gallonage vs height based on the tapered shape of the tank.;D
Heck, we should just design a tank like some motorcycles and small utility engines, with a clear panel in the tank (gas gawker?%)) with nice graduations!
Now that's a tank I'd like to have in mine. A backup for a failed gauge.

Paul

We could get really fancy and do some sort of in-cab sight glass like some of the old ones used for underground fuel tanks. Not sure how they worked but they were above tank level inside the building.

 

[Viperwolf1]

We could get really fancy and do some sort of in-cab sight glass like some of the old ones used for underground fuel tanks. Not sure how they worked but they were above tank level inside the building.

Just add a dipstick.