map/boost over OBD2 on evo9

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Jul 30, 2021 | 08:14 AM

orion4096

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map/boost over OBD2 on evo9

I have an evo9 with an aeroforce OBD2 gauge that replaced an AEM boost gauge using the analog input and AEM sensor. It worked for several years but eventually the sensor failed. Went through 2 ebay sensors which also failed in a few months and finally gave up. It's frustrating that the 8/9s come stock with 1 bar MAP sensors and the JDM/X sensor doesn't have the right scaled output over OBD2. So I decided to modify the scaling as a small project to learn more about the ECU:

This code is 2 cases in a switch statement for LTFT and MAP output to OBD. It's basically filling in some data into RAM which represents the packet. The compiler left a bunch of NOPs in the delay slots which helps to make room for more code without branching somewhere.

Code:

0003A9D0 sub_3A9D0:       64 13  mov r1, r4     ! XREF: word_3A88A
0003A9D2                  B4 91  bsr sub_3B2F8
0003A9D4                  00 09  nop
0003A9D6                  DA 3F  mov.l @(0xFC,pc), r10
0003A9D8                  2A 01  mov.w r0, @r10
0003A9DA                  A0 C3  bra sub_3AB64
0003A9DC                  00 09  nop

0003A9DE sub_3A9DE:       DA 3E  mov.l @(0xF8,pc), r10
0003A9E0                  6A A1  mov.w @r10, r10
0003A9E2                  6A AD  extu.w r10, r10
0003A9E4                  4A 01  shlr r10
0003A9E6                  DB 3B  mov.l @(0xEC,pc), r11
0003A9E8                  2B A1  mov.w r10, @r11
0003A9EA                  A0 BB  bra sub_3AB64
0003A9EC                  00 09  nop

Here is the modification where the MAP value is scaled up by 1/4+1/16 for the JDM sensor. It's missing a saturation check and could use another 1/32 increase.

Code:

0003A9D0 sub_3A9D0:       B4 92  bsr sub_3B2F8  ! XREF: word_3A88A
0003A9D2                  64 13  mov r1, r4
0003A9D4                  DA 3F  mov.l @(0xFC,pc), r10
0003A9D6                  A0 C5  bra sub_3AB64
0003A9D8                  2A 01  mov.w r0, @r10

0003A9DA sub_3A9DA:       DA 3F  mov.l @(0xFC,pc), r10
0003A9DC                  6A A1  mov.w @r10, r10
0003A9DE                  6B A3  mov r10, r11
0003A9E0                  4B 09  shlr2 r11
0003A9E2                  3A BC  add r11, r10
0003A9E4                  4B 09  shlr2 r11
0003A9E6                  3A BC  add r11, r10
0003A9E8                  DB 3A  mov.l @(0xE8,pc), r11
0003A9EA                  A0 BB  bra sub_3AB64
0003A9EC                  2B A1  mov.w r10, @r11

Now I have a working boost gauge using OBD2 without having to worry about wiring an additional sensor that will fail. The engine and turbo are stock so the 8-bit MAP value is enough to cover the boost range.

The code output comes from sh2dis which is great for getting a quick text disassembly.

JDM map sensor: https://www.evolutionm.net/forums/ec...tructions.html
disassembler: https://www.evolutionm.net/forums/ec...assembler.html

Jul 30, 2021 | 08:22 AM

Biggiesacks

EvoM Community Team Leader

Joined: Aug 2005

Posts: 5,690

Likes: 708

From: West Coast

Nice!

I love seeing folks still tinkering around with the stock ecu. If it helps, this online dissasembler has SH2 support, and will calculate the PC relative addresses for you.

https://onlinedisassembler.com/static/home/index.html