Z32 VQ map 64 values vs. voltage

RomChip200 · Post by **RomChip200** » Tue May 12, 2009 11:58 pm

Nistune reports in the table a max. voltage of 5.12V for the 64th value that would mean a resolution of 0.08V regarding the ADC of the ECU.
But some software as ZTalk report some voltages of 5.7V in my logging session @ full boost. Many times, it goes over 5.1V @ full boost.

Where is the truth ?

I'm pretty sure the 65535 value is not taken @5.12V but for a higher voltage.
I can tell this b/c when I reach 5.1V, my real TP (recorded in my ECU) is not so high and it corresponds to the 14th column of my fuel map. This is crosschecked by looking to the corresponding timing value.
Applying the TP formula and injecting VQ=65535 gives really a higher TP than the real recorded one.

A resolution of 0.1V would be better for me (max. 6.4V), that would corresponds to a VQ=~33000 for 5.1V, and then, calculated TP follows the real TP.

Matt, have a look to my log, you will catch my point.

Matt · Post by **Matt** » Thu May 14, 2009 10:33 pm

5.12 comes from 512 (2^9) the resolution of the A/D converter on most ECUs

So the ECU in most cases can only read upto 5.12 volts. It shouldnt process voltage any higher

Matt · Post by **Matt** » Sun May 17, 2009 2:44 am

just thinking that perhaps some ECUs have 10 bit A/D converter which would allow 0-1024 perhaps? I'll have to exercise input voltage on one of my bench ECUs (Z32?) and see what it reads upto

added to my investigate list

RomChip200 · Post by **RomChip200** » Mon May 18, 2009 4:49 am

I'm probably wrong (and Ztalk from xtensive also) and you're probably right because when taking the maf register, Nissan documents tell to multiply the value per 5mV to get the real voltage, and you display it correctly in Nistune.
Ignition on: maf register = 0x10
16 *5mV = 0.08V

I managed to get ~4.15V @7.7psi