Bullnose Enthusiasts Forum

fuel gauge reading high with new senders

Classic

List

Threaded

28 messages Options

delco1946

fuel gauge reading high with new senders

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.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

taskswap

Re: fuel gauge reading high with new senders

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?

--
1981 F-250 Custom. 6.6L V8, 4 barrel Holley carb, ARA aftermarket A/C.

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

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 (R), so .5 x .5 x 2 = .5 watt.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Rembrant

Re: fuel gauge reading high with new senders

In reply to this post by delco1946

delco1946 wrote

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.

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

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

Gary, AKA "Gary fellow": Profile

FuzzFace2

Re: fuel gauge reading high with new senders

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 ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

delco1946

Re: fuel gauge reading high with new senders

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!

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

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.

Gary, AKA "Gary fellow": Profile

Megiddo

Re: fuel gauge reading high with new senders

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.

1984 F250 4x4 351W ZF5-42

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

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.

Gary, AKA "Gary fellow": Profile

ratdude747

Re: fuel gauge reading high with new senders

In reply to this post by Rembrant

Mine (a Spectra OE sending unit) seems to be right at the top and bottom of the scale... but it's like the sending unit has an exponetial response curve compared to the gauge.

At full, it's full. But it drops off very quickly to 1/4 (roughly half a tank), and then slowly drops to E. Which would fit with an exponential output feeding a linear gauge (1/2 squared is 1/4, after all). Short of brute forcing an arduino based custom board, I don't know of a good passive way to fix that... and I'm drawing a blank on how to do it with single-supply OP-amps.

1984 F150: 300 L6, AOD, RWD. EEC IV / TFI, Feedback Carter YFA Carb. Stock everything but radio (for now).

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

The thread Bricknose Sender to Bullnose Gauge Interface has an overall diagram awa an outline of the sketch.

What hasn't been included in the sketch is reading the output of the tank selector switch and then choosing which of two different curves to use.

And, speaking of the curve, it appears to use a straight line, but we need to allow an exponential curve. So the equation needs to be a bit more complex. But that's not difficult.

HOWEVER, I'm running a MeterMatch. For $84 it does a pretty decent job of interfacing a Bricknose sender to Big Blue's Bullnose gauge. And while it doesn't truly allow for an exponential curve it does provide 4 points on the curve to calibrate it, so you'd have three straight lines that could approximate the curve.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

Update: I bought from Technoversions, and I believe they designed it. And it is $75 inc shipping. Plus there's a good writeup on how it works.

Gary, AKA "Gary fellow": Profile

Machspeed

Re: fuel gauge reading high with new senders

Administrator

Interesting conversation and a project I will be delving in to soon.

Larry, my gauge, when it was working, was just as you described.....seemed to stay on full for some time then drop quickly to a quarter and hold there for awhile. When that needle hit the line, you were out of gas. Ask me how I know!

John

"Blackie" - 1986 F150 4x4 - Mildly warmed over 351W HO - Original owner

Gary Lewis

Re: fuel gauge reading high with new senders

Administrator

Dad loaned me his '72 Mustang when our Citation was in the shop for one of its many recalls. I pulled into the driveway as the needle touched E. The next morning it would not start. He said "Sorry, I forgot to tell you that."

With the MeterMatch you fill it to the point you want it to show Full and hit the button to calibrate for Full. Drive it to where you want it to read in the middle of the scale, say 2/3's, and hit that button. Then maybe 1/3 and hit that button. And finally where you want it to be for Empty and calibrate there.

But, you only have one "map" and both tanks read off that. Unless you buy two MeterMatches and wire them in ahead of the switch instead of after.

Gary, AKA "Gary fellow": Profile

Machspeed

Re: fuel gauge reading high with new senders

Administrator

Gary Lewis wrote

With the MeterMatch you fill it to the point you want it to show Full and hit the button to calibrate for Full. Drive it to where you want it to read in the middle of the scale, say 2/3's, and hit that button. Then maybe 1/3 and hit that button. And finally where you want it to be for Empty and calibrate there.

But, you only have one "map" and both tanks read off that. Unless you buy two MeterMatches and wire them in ahead of the switch instead of after.

Thanks Gary, won't be buying two MeterMatches so will just figure out a way to make the sending units work.

John

"Blackie" - 1986 F150 4x4 - Mildly warmed over 351W HO - Original owner

FuzzFace2

Re: fuel gauge reading high with new senders

If the gauge reads right at empty but not full, over full, bending the float arm is not going to get it right as pointed out the empty reading will now be off.
You need to move the full level arm stop lower so the arm will not go up as far.

Again I dont care were it reads when full but I dont want to be running out of gas when showing 1/8 tank. Had a Toyota LC that happened all the time on after the 4th time, each heading to a station, I bent the arm to read empty with a few gallons in the tank. Dont remember what it read when full as I cant remember ever filling it, kid and no money LOL
Dave ----

delco1946

Re: fuel gauge reading high with new senders

Hey Dave, not to be a dunce but where is this stop you speak of an how does one adjust it? Not sure what brand I have but here is one, I’m not seeing any obvious stops that one could adjust to correct a “full” reading.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

taskswap

Re: fuel gauge reading high with new senders

I can't speak for any stops but it was common in Subaru Imprezas I used to own to just bend the arm a bit. They were notorious for reading full-E with a few gallons still in the tank, and reading 1/8th past F when full.

--
1981 F-250 Custom. 6.6L V8, 4 barrel Holley carb, ARA aftermarket A/C.

FuzzFace2

Re: fuel gauge reading high with new senders

In reply to this post by delco1946

delco1946 wrote

Hey Dave, not to be a dunce but where is this stop you speak of an how does one adjust it? Not sure what brand I have but here is one, I’m not seeing any obvious stops that one could adjust to correct a “full” reading.

I cant really see from that picture but some senders have a metal tab the metal arm hits that might be adjustable?

I was talking to a member to day about this and he said to get the E / F to read right, with a lot of testing, he had to bend the arm it 2 places.
One to read right for E and then one for F.
If you only did the 1 bend of the arm it would only read right for E or F.

All this testing is best done with bed off truck.
Dave ----