About ALTEZZA fuel gauge

[mokh]

I changed the fuel system to return type. So the presure shall be map reference right?

The injector used is upgraded from oem caldina st206, 540cc. Injector data taken from turbo basemap apexi power fc based on this injector.

Still working on the tune...thanks for the advise. Will look into it.

Im idling at 15afr. Cruising at 14.3, accelerate at 12~13.

Didnt push it much for now. (Not more than 0.6bar)

 

[Adamw]

Map referenced is correct for a return system.  Your high VE numbers suggests either fuel pressure is low, injectors flow less than 540cc, or your deadtimes are wildly wrong.

[mokh]

Will it effect the fuel gauge reading?

[Adamw]

Yes.  The ECU sends fuel consumption data to the dash which uses this to control the gauge.  I dont know exactly how the gauge works as it it quite complicated, but it shows a combination of "fuel level" in the tank, and "distance until empty" based on fuel consumption or one or the other under certain conditions. 

Since the ecu thinks you are using much more fuel than it actually is, the data it is sending to the fuel gauge is exaggerated and your gauge goes down faster.

[Tom H]

Hi there, just bringing an old thread back to life. 

I have recently installed a G4x PNP into a 1999 Altezza but have used a traditional fuel map. The fuel gauge reads full all of the time, something I didn't notice at the time of tuning. 

Reading the above thread, the issue is likely to be the mapping, which I will need to change to modeled/VE? Or has there been some allowance for different tuning strategies since the last post in 2020? 

There could be other issues as well. The car now has a 2JZ and has been converted to have a return fuel system. Possibly there is a mechanical issue as well. I haven't got access to the car at the moment so I can't check further. 

Any help appreciated. 

Tom 

[Adamw]

Yes you need to use modelled mode for the fuel gauge to work properly.  The fuel mass per cylinder needs to be transmitted so modelled mode is needed for the ecu to have enough info to calculate fuel mass.  

However, this wont prevent the fuel gauge from working at all, it will just move in odd increments, something like a 1/4 tank at a time.  So if yours is reading full all the time and you've used more than a 1/4 of a tank then I would say that the tune isn't your issue. 

[DerekAE86]

7 minutes ago, Adamw said:

However, this wont prevent the fuel gauge from working at all, it will just move in odd increments, something like a 1/4 tank at a time.  So if yours is reading full all the time and you've used more than a 1/4 of a tank then I would say that the tune isn't your issue. 

So does it use a traditional sender unit for course fuel level and then the calculation over BEAN to fill in the gaps?
What changed for 2001+? The BEAN protocol? 

[Adamw]

There is very little info on how it actually works, but it acts more like a predicted "distance to empty" gauge rather than just a fuel level gauge.  It seems like it "calibrates" when the fuel level passes certain thresholds - so it always reads full after you fill up and always reads empty when it is near empty, but for a lot of the range in between those points it uses fuel mass flow and speed/distance to display how much range you have left.  

[OzoneNZ]

@Adamw and the Link folks did some incredible reverse-engineering work on the MPX protocol with the AltezzaLink's CAN <=> MPX translation abilities - MPX is awful because it's not CAN, and was very quickly phased out of Toyota vehicles in favour of standardized CAN - any and all MPX technical documentation I've come across was in Japanese and not specifically targeted at the Altezza's MPX variant.

Warning that the below is not proven gospel at all, just my observations and reverse-engineering efforts since 2016

As @Adamw said the Altezza clusters are MPX-connected and the fuel gauge is a pain in the ass - it's hard to 100% confirm the scaling logic and values it operates with, but I can confirm it uses both the tank level sender AND instantaneous consumption metrics coming in from the MPX bus.

My Altezza got a G4+ with a modelled fuel tune back in 2016 and immediately I hit the inop fuel gauge issue - blessing in disguise I guess as it did allow me to pick out certain details of how the gauge works:

- If the cluster/fuel gauge receive no instantaneous consumption metrics via the MPX bus, it'll drop in ~1/4 increments about every hour or so - this is what the cluster appears to do when it only has the tank level sender as a reference.

- Even if you have instant consumption MPX data flowing to the cluster, it will still consult the tank level sender regularly to recalibrate - this is why filling an Altezza that has an inop fuel gauge due to missing MPX data will still result in the fuel gauge springing to full immediately.

The above is really funny to observe when your MPX values are scaled too high and drop the fuel needle too quickly, then the gauge reconciles its level against the tank level sender, and the needle can go back up

Long story short - I mostly solved my inop gauge via a few days of backroad driving, a MacBook on the passenger seat, and heinous amounts of multiplier/divider tweaks to the CAN/MPX packet values in the image attached:

 

My modelled tune isn't particularly accurate to be honest, so the raw 1/1 mult/div values being sent from the G4+ to the fuel gauge would've been way off - what this led to in practice was a fuel gauge responding to the Link's consumption metrics, but it would go from Full to Empty over ~100 km.

Playing with the mult/div combination and wasting 98 Octane on backroads, I've found the 1/3 combo to scale almost perfectly for me!

Mult/div combinations will heavily depend on your tune and how accurate the VE metrics/calculations your Link is operating with are - if your VE is waaaay off, you can still get the gauge working and scaled properly, but you're really better off fixing the tune first and THEN playing with the mult/div rather than masking the issue.

We're very lucky that Link NZ has the AltezzaLink on the market as MPX was only present in a limited number of production years, and a total pain in the ass that the rest of the big ECU giants decided wasn't worth the effort  - big props!