E38 fuel level sensor calibration

[harascho]

One thing I didn't care about in my swap (2007 5.3 LMG in 1997 2dr 4wd Tahoe)
is the fuel level sensor. I had to built a new connecting rod for the level sensor, 'cause the '97 Tahoe's gas tank is a lot deeper than the 2007 composite tanks.
I also had to modify the fuel pump module to fit that deep tank.


http://i301.photobucket.com/albums/nn67/harascho_album/IMG_3524.jpg

http://i301.photobucket.com/albums/nn67/harascho_album/IMG_3527.jpg

http://i301.photobucket.com/albums/nn67/harascho_album/IMG_3531.jpg

http://i301.photobucket.com/albums/nn67/harascho_album/IMG_3533.jpg

The manual states 40ohms resistance for a full tank and 250 ohm resistance for the empty tank. The E38 sees 5V for the empty tank and 0V for the full tank. In my 1997 Tahoe gas tank I could manage to have 250ohms empty and 50ohms full.... not exact but close to the spec.

Then I looked up the calibration in EFIlive : There is F0504 which is the tank capacity in liter and F0505 as sensor calibration.
I have F0504 113l. When I read those values with the scan tool:

http://i301.photobucket.com/albums/nn67/harascho_album/sensor_pid.jpg

I recieve 0.8V for a full tank. Seems ok so far but what seems strange to me is I read 99l as Fuel tank rated capacity GM.FTRC although I programmed F0504 113l in the tune tool.

http://i301.photobucket.com/albums/nn67/harascho_album/tank_size.jpg

any ideas? Did I miss something?
best regards from Germany

Harald

[gmh308]

One thing I didn't care about in my swap (2007 5.3 LMG in 1997 2dr 4wd Tahoe)
is the fuel level sensor. I had to built a new connecting rod for the level sensor, 'cause the '97 Tahoe's gas tank is a lot deeper than the 2007 composite tanks.
I also had to modify the fuel pump module to fit that deep tank.

The manual states 40ohms resistance for a full tank and 250 ohm resistance for the empty tank. The E38 sees 5V for the empty tank and 0V for the full tank. In my 1997 Tahoe gas tank I could manage to have 250ohms empty and 50ohms full.... not exact but close to the spec.

Then I looked up the calibration in EFIlive : There is F0504 which is the tank capacity in liter and F0505 as sensor calibration.
I have F0504 113l. When I read those values with the scan tool:

I recieve 0.8V for a full tank. Seems ok so far but what seems strange to me is I read 99l as Fuel tank rated capacity GM.FTRC although I programmed F0504 113l in the tune tool.

any ideas? Did I miss something?
best regards from Germany

Harald

Nice mod there Harald.

Does the ECM OS you are using normally look for a 2 sensor setup?

[harascho]

good question...
I am using the following VIN of a 2007 Tahoe as data source.
The ECM, TCM, BCM, Cluster and TCCM are updated via TIS to the latest tunes based on that VIN

1GNFK13037R238413

As far as I know a Tahoe only uses one fuel level sensor but I am not 100% sure..

Harald

[harascho]

http://i301.photobucket.com/albums/nn67/harascho_album/tank_size.jpg

http://i301.photobucket.com/albums/nn67/harascho_album/sensor_pid.jpg



Maybe I'm wrong, isn't GM.FTRC exactly what I set with F0504 in the tune??? If yes then there is something wrong cause a F0504 of 113litres returns a GM.FTRC of 99litres regardless what I do with F0505.

I would expect if I set F0504 to 113litres that I can see this in GM.FTRC as 113 litres and that the calibration of F0505 then should be set to 113litres at 0V fuel level sensor voltage?



a still confused Harald

[harascho]

if anyone is interested here are the logs

[gmh308]

At a guess, 99L tank is probably the max size that is catered for by the OS/fuel segment. The number may have scope to get above 99 like your 113L, but there is more to the fuel cal than just the tables shown.

If your gauge reflects the sender level, then the cal is probably for a single sender tank. If it was a two sender tank, then it would do wierd things with one sender. (based on first hand experience :doh2: ).

[GMPX]

ok, I did a bit of searching for you. The PID value you see is not actually derived from the sensor scaling and calibrations, instead it is just a single calibration value that is used solely to report the fuel tank size, so it's almost useless. This is why you don't see anything change.

[gmtech16450yz]

Does your OS have F0505 "Primary Fuel Tank Sender Calibration"? If it does, just use it to recalibrate your gauge to read correctly with the different tank/sending unit setup. Raising values makes the gauge read higher, lowering them lowers gauge reading.

Oh, just re-read your posts, you do have F0505 but it doesn't seem to be changing? Do you mean the gauge itself isn't changing? It should. Try putting some drastically different numbers in F0505 and see if your gauge reads differently. I wouldn't worry about it if F0504 doesn't change.

[harascho]

'had some spare time today. I connected a poti to the fuel level sensor inputs of the E38 and did some research.

I divided the gas gauge scale in 8 sections E to 8/8 (F).
Then I checked which resistance I need with the calibration on top of this thread to have the gas gauge exact at the 8 levels I created. In the same time I watched the FLS and FuelRem with the scan tool.

Here we are:


http://i301.photobucket.com/albums/nn67/harascho_album/calibration_1.jpg

Interesting that the min sensor Voltage is 0,84V at 50R and the max sensor Voltage is 2,53V at 250R fuel level sensor resistance.... The table in the tune file starts at 1,4 V - 5V . It looks like there is factor 2 somewhere between?

Adjusting the F0505 to the values of my table brought no success. I ended with 6/8 gas gauge reading at 50R level resistance..?
I reloaded the tune file above and the gaugedidn't read that bad.... I made a big circle and ended at my starting point.... or are my thoughts wrong ?

Harald

[gmh308]

'had some spare time today. I connected a poti to the fuel level sensor inputs of the E38 and did some research.


Interesting that the min sensor Voltage is 0,84V at 50R and the max sensor Voltage is 2,53V at 250R fuel level sensor resistance.... The table in the tune file starts at 1,4 V - 5V . It looks like there is factor 2 somewhere between?

Adjusting the F0505 to the values of my table brought no success. I ended with 6/8 gas gauge reading at 50R level resistance..?
I reloaded the tune file above and the gaugedidn't read that bad.... I made a big circle and ended at my starting point.... or are my thoughts wrong ?

Harald

Admirable achievement getting this working as well as you have. :)

All late model GM fuel level setups we have seen run with a 0-2.5V range.

Yes the port for the fuel level offers a standard 5V supply when measured with a meter, but the output impedance/resistance of the port is roughly equal to the total tank sensor resistance, so 2.5V across the tank sensor.

[joecar]

I agree, very good job Harald...:cheers:

[harascho]

Thanks guys for your praise.... ;-)

So as I have full and empty according to the gauge I shouldn't change anything in the calibartion here??

http://i301.photobucket.com/albums/nn67/harascho_album/sensor_cal_3.jpg

let it be like that, but what is with the "fuelRem" it is still related to the initial max tank size F0504 which I set to 113 but the FTRC only reads 99l all the time, no matter what I set F0504.
As GMPX said FTRC its only cosmetic.... I am not that sure about this... Some DIC messages need the tank's size to calculate other information as distance to empty for example. Also as you can see in my table the fuel rem is also based on a 99l tank... not the desired 113l one....

I guess I should stop here and leave it like that... it's not perfect...but.... ?

Harald

[GMPX]

I ran out of fuel in my 2000 Holden with 40Km's to go on the DIC.......it's not perfect is the motto at Holden as well by the look of it.

[ScarabEpic22]

I ran out of fuel in my 2000 Holden with 40Km's to go on the DIC.......it's not perfect is the motto at Holden as well by the look of it.

Really? Wow, even after my light comes on and says I have less than 20mi to go I can usually go another 20-40mi depending if its on the hwy or around town. Have approx 1.5-2.5gal left.