[b3lha]

I just bought another SVX ECU for research and it wasn't quite what I expected. I think it's a very early USDM version, label is D1 rather than the usual M7.

The circuit board is slightly larger (see photo). The D1 is on the left compared with the regular D2 from my JDM on the right. The small chip in the top left corner is external ROM. I guess that when this ECU was made, the M37791 MCU wasn't yet available in a 32K version, so they had to use external.

The original firmware is 722521. At some point it has been upgraded with a chip containing the 1993 firmware 722527.

I compared the 722521 firmware with the USDM 92 firmware 722525. The timing maps and MAF scale are the same but the fuel map is very slightly different.