fuel gauge reading high with new senders

[delco1946]

I had my mechanic install new everything related to my fuel system. Originally, I was hoping to reuse the senders though, and thus I did not order them, rather my mechanic did later. I ordered the tanks, vents, pump, hosing etc. Fast forward - both measure empty when empty(whew), but both the rear and front tanks now register quarter inch+ to the right of full when full.

This drives me crazy. Why is this and how can I fix it? I didn't order them, so I can't verify that they are the right units but I obviously have to assume so.

[taskswap]

I can't seem to find the thread but if you search the forum I seem to recall there being two resistance levels for senders. Are you able to measure the resistance at full and empty to confirm your range and report it back here?

[Gary Lewis]

I can't seem to find the thread but if you search the forum I seem to recall there being two resistance levels for senders. Are you able to measure the resistance at full and empty to confirm your range and report it back here?

There are two different senders - the Bullnose ones and the later ones. But if your readings are roughly right you didn't get the later senders as they are completely backwards. The Bullnose senders run from 10 ohms at Full to 73 ohms at Empty while the later senders are something like 16 ohms Empty to 160 ohms Full. Yes, backwards as well as different.

If you want to "calibrate" your fuel gauge you could replace your ICVR with an adjustable voltage regulator and adjust it until your fuel gauge reads Full when one of the tanks is full. But that will also "adjust" the other two gauges, the coolant temp and oil pressure, down a bit. And, you can't adjust each tank.

To adjust each tank w/o impacting the other gauges you could put a very small resistance in the wire to each tank. For instance, you could try a 1 ohm or a 2 ohm resistor in series with the sending unit. That will bring the upper end of the reading down a bit but probably won't make much difference on the bottom end as 1 or 2 ohms vs 73 ohms won't make much difference.

However, the resistor has to have a least a 1 watt rating. I've measured ~.5A in the gauge circuits at full scale. And wattage is current (I) x current (I) x resistance ®, so .5 x .5 x 2 = .5 watt.

[Rembrant]

This drives me crazy. Why is this and how can I fix it? I didn't order them, so I can't verify that they are the right units but I obviously have to assume so.

I went through this with my '84, but mine wasn't reading over-full, it was reading under full...like 1/2 or 3/4 tank when full. This drove me crazy because it would show empty but then only tank a half a tank worth of gas to fill.

Anyway, I took the sender out, and I just kept bending the float arm and testing it over and over again until I go it close. What I did specifically was start with the tank empty, then put in 10L (2.5 gallons approx), and kept adjust the float arm until it sat right on the "E", or a hair below it. Once I did that, it also read full properly. The down side of this was that I bent the float arm downwards enough that I ended up having to also bend the pickup tube down even lower as well (or the truck would have run out of gas before it read empty). After all that, it worked great.

That was a fairly tortuous path to take to get a gas gauge reading properly, but they were all brand new parts, and I was lucky enough to have made all of these float adjustments while the bed was removed, so I didn't have to drop the tank.

I thought I was being a real keener by checking the new sending unit before installing it...I made sure that it worked with my gas gauge before putting it in the tank. What I didn't know then, but I DO know now, is that I should have also compared the new sending unit to the old sending unit to make sure the float range of sweep was relatively the same between the two.

I could be way off base here, but I think that some of the aftermarket senders are fine electrically, but just not bent/formed correctly.

 

[Gary Lewis]

This drives me crazy. Why is this and how can I fix it? I didn't order them, so I can't verify that they are the right units but I obviously have to assume so.

I went through this with my '84, but mine wasn't reading over-full, it was reading under full...like 1/2 or 3/4 tank when full. This drove me crazy because it would show empty but then only tank a half a tank worth of gas to fill.

Anyway, I took the sender out, and I just kept bending the float arm and testing it over and over again until I go it close. What I did specifically was start with the tank empty, then put in 10L (2.5 gallons approx), and kept adjust the float arm until it sat right on the "E", or a hair below it. Once I did that, it also read full properly. The down side of this was that I bent the float arm downwards enough that I ended up having to also bend the pickup tube down even lower as well (or the truck would have run out of gas before it read empty). After all that, it worked great.

That was a fairly tortuous path to take to get a gas gauge reading properly, but they were all brand new parts, and I was lucky enough to have made all of these float adjustments while the bed was removed, so I didn't have to drop the tank.

I thought I was being a real keener by checking the new sending unit before installing it...I made sure that it worked with my gas gauge before putting it in the tank. What I didn't know then, but I DO know now, is that I should have also compared the new sending unit to the old sending unit to make sure the float range of sweep was relatively the same between the two.

I could be way off base here, but I think that some of the aftermarket senders are fine electrically, but just not bent/formed correctly.

That's very good info, Cory. And it makes sense. Thanks.

[FuzzFace2]

That's very good info, Cory. And it makes sense. Thanks.

Like Cory I tested mine before the bed went back on.

I did not care where it reads when full as long as it reads right when close to empty.

Tanks empty the needles are below the mark.

With 5 gallons in each tank the needles come up even to the mark and that is good with me.

When the needle in on the empty mark I still have 5 gallons to get to a station.

Now when full both tanks read above full and I dont have a problem with that as I will not run out of gas when full like I would if the gauge was say 1/8 tank and not reading right.

If I wanted to fix the full I would bend the arm stop on the full swing so it would not go up as far but keep the empty stop where it is.

Now if I can keep the temp gauge from reading differently at times I would be happy.

One time it can be on the low line and the next time in the middle, I like the middle as I think the motor has some heat in it. No it is not running cold as the heat will cook you out. The sender is new but the connection may be dirty and need to check it.

Dave ----

[delco1946]

Like Cory I tested mine before the bed went back on.

I did not care where it reads when full as long as it reads right when close to empty.

Tanks empty the needles are below the mark.

With 5 gallons in each tank the needles come up even to the mark and that is good with me.

When the needle in on the empty mark I still have 5 gallons to get to a station.

Now when full both tanks read above full and I dont have a problem with that as I will not run out of gas when full like I would if the gauge was say 1/8 tank and not reading right.

If I wanted to fix the full I would bend the arm stop on the full swing so it would not go up as far but keep the empty stop where it is.

Now if I can keep the temp gauge from reading differently at times I would be happy.

One time it can be on the low line and the next time in the middle, I like the middle as I think the motor has some heat in it. No it is not running cold as the heat will cook you out. The sender is new but the connection may be dirty and need to check it.

Dave ----

Cory - i thought about doing that, but at this time its empty when reading empty, so if I adjust the rage/seep by bending it, I assume the empty reading will become less accurate (?).

Dave - my mechanic said the same thing as you lol, but i'd still like it to be accurate all the time. It bums me out cuz the the front sender was working fine, it just seemed smart to replace them both while in there .

I might try the resistor trick, I have lots lying around!

[Gary Lewis]

Cory - i thought about doing that, but at this time its empty when reading empty, so if I adjust the rage/seep by bending it, I assume the empty reading will become less accurate (?).

Dave - my mechanic said the same thing as you lol, but i'd still like it to be accurate all the time. It bums me out cuz the the front sender was working fine, it just seemed smart to replace them both while in there .

I might try the resistor trick, I have lots lying around!

It is easy enough to try. Fill it up, slide under and pull the wire off the mid-ship tank as it is easy to get to, put the resistor in the line, and turn the key on.

You can put several resistors in parallel to get the resistance you want, and to raise the wattage rating.

[Megiddo]

It is easy enough to try. Fill it up, slide under and pull the wire off the mid-ship tank as it is easy to get to, put the resistor in the line, and turn the key on.

You can put several resistors in parallel to get the resistance you want, and to raise the wattage rating.

I have this problem too and have been wondering about bending the float arms. My front tank won't quite show full, but my back tank runs dry before empty. I have to use my trip odometer to guess my fuel status.

[Gary Lewis]

I have this problem too and have been wondering about bending the float arms. My front tank won't quite show full, but my back tank runs dry before empty. I have to use my trip odometer to guess my fuel status.

Man, I really should have built the Arduino for that! I have the sketch (program) already written and tested.

IIRC, it allows you to tailor the curve the whole way. Raise or lower either the Empty or Full reading. And it takes its input from the tank switch so it can tailor the curve for each tank separately.

Haven't looked at it in a couple of years, but if someone wanted to pick up the cudgel and make it happen I'd happily pass on what I have.