Fuel level shows wrong

[Zahri]

Hi! I'd love to hear some opinions on my problem. I am currently trying to deal with it at the dealer but its useless...

So my problem .. When I discovered the problem fuel level ( I have digital cluster) showed full tank all the time. Even If I had last quarter. Then at dealer they did some calibration and didnt help. They took out the sender unit out and its working as it should. On diagnostics fuel sender shows exact and correct amount of fuel but then on display it shows still wrong. After next tunes at delaer it's now partially working. When I fill up tank my display shows me around 60% of fuel. But when I get acutal 60% in my tank (From 100 to 60% It doesn move at all) It starts to work all the way down to the 0%. Also estimated range is calculated for those 60% of fuel tank. So in those upper 40% I dont know what is my fuel level and my est. range. Its under warranty but what the hell... In total I was 2 and half month without car and still not working. Currently I got a new digital cluster but nobody believe that this is a fix. Any advice? thx

Ford Fiesta ST mk 8.5, 1.5 eco

 

[Intuit]

Sounds like it is working now, but just needs calibrated again.

What year is the vehicle?

 

[M-Sport fan]

^^^It has to be a 2017 to current, since that is the time frame of the Euro/rest of world, Mk8 Fiestas/FiSTs.

I did not know that Ford did any 8.5 type revisions on the Mk8s, but if so, it might be even more current than 2017.

 

[Zahri]

Well its not working like it should. Dashboard is now changed and it didnt help. Still behaves the same way. Fill the tank and it shows around 60% until I burn upper 40% then its working. They tried to calibrate it few times and didnt help as well.

Its Fiesta ST mk8.5 (facelift) from 2022

 

[SteveS]

I would guess the problem is with the float/sending unit in the tank.

 

[Intuit]

Yeah that is a possibility as well. The dash was bad, they replaced the sender but installed incorrectly, replaced the dash, now you're left with the incorrectly installed sender. I was guessing that they didn't calibrate correctly. Most calibration routines involve finding the min/max.

Need raw signal from the sender. ForScan might be able to query the BCM for that info. If not look at a wiring diagram and probe with a voltmeter.

 

[Zahri]

I am now booked at the different dealer. So I will see once they will make time on me.

There is still one strange detail. On diagnostics tool they saw two different Fuel levels. One is directly from sender unit and next one was shown from ECU i suppose. At that time I had 87% of fuel in tank. Sender unit "saw" this exact amount on diag. But 2nd number from ECU was showing wrongly 70% on my display.

 

[Intuit]

The BCM / ECU maintains an 'estimated to empty' miles/kilometers. For my previous and this one, the gauge seems to vary depending on consumption habits. So if I turn on the A/C compressor which creates a significant dent in MPG, it seems like the gauge reads lower with more fuel in the tank. I don't know whether this is actually occurring or not, but it seems like it does. IF I'm not completely imagining things, this might explain what that is.

 

[Zahri]

Well I know about this "feature" but gauge shows 70% even if I have full tank. Estimated range is also only for those 70% of fuel. So When I fill the tank I see on my dash stable 70% of fuel and my estimated range around 350km (which is for those 70%) and it is slightly changing due to driving style (town, highway....) After around 200 driven kms fuel gauge start to move down with estimated range to 0 as it should. But next tank and same story again.