JDM B20A ECU revealed (PH3)

[carotman]

Ok, I just got my 88-89 JDM PH3 ECU. I opened it and was totally amasez by what I saw. The PH3 ECU shares the S-A-M-E PC board as the USDM B20A5 PK2 ECU. There are slight differences in some places but it's overall the same. This might be due to the fact that the PK2 uses 2 O2 sensors while the PH3 uses one. The PH3 I have is for an Auto car also (there shouldn't be any difference tough).

This means that the PH3 and PK2 programs should me the 99.99% similar except maybe the fuel and timing curves...

I will post both pictures just to show you guys how it looks!

[AccordEpicenter]

Good find... i cant wait to see pics... B20a stuff is htf

[carotman]

Here's the 88-89 PH3 scan from the ECU I got
JDM 88-89 PH3

If you compare it to the PK2 ECU, you can see that it's the exact same ECU with slight differences
USDM 88-89 PK2 (Thanks to PGM-FI.org)

For your info, here's the 86-87 PH3 ECU posted by thegreatdane
JDM 86-87 PH3

You can see that the 86-87 is VERY different from the others.

[Kabuki]

Well, son of a bitch! Has anyone tried loading up one of the PK2 or PH3 ROMs on TurboEdit? They use the same processor, and a VERY similar board setup to the OBD0 PR4 and PM6 boards. Interesting...

[thegreatdane]

So the accord actually shares ECU's with two generations of preludes. Interesting.

The ecu is probably just plug and play with your existing harness then. When will you be testing the ecu?
But wasnt the ecu listed as a manual trans ecu?


Kabuki, TurboEdit and other OBD0 editors cant read the PH3 roms.

[carotman]

Well, I found something good today. I was comparing both ECUs and I'm pretty sure they have the same pinout. When I checked pin B11 on the PH3 (Secondary O2), I realized that it had a diode not present on the PK2 ECU

PH3 Secondary O2 Bypass

What this diode does is basicaly connect the Pin B11 to ground, disabling any input going to pin B11. All the circuity for the secondary O2 is there but it's just disabled by the diode. I'm pretty sure that it's also disabled in the ROM also but maybe not. The PK2 doesn't have this diode and will use the secondary O2 input. I wonder if the secondary O2 would be disabled if you just put a diode in there (without getting a CEL)

There are a couple of other differences I haven't been able to figure out yet but it might come from the fact that the PH3 has the board number 11101-XA1-0001 while the PK2 has board number 11101-XA1-0011. This just could be a board revision and both ECUs are totally compatible. I know that Honda used different PC board for their ECUs while keeping the same ROM. (Like the P06).

I have asked people on Preludepower.com to post their board numbers so we can compare stuff.

I won't be able to test the ECU until this spring since my car is stored. I may have access to a 3rd gen Prelude tough.

[Kabuki]

Kabuki, TurboEdit and other OBD0 editors cant read the PH3 roms.

Which PH3 ROM though, the 86-87 or the 88-89? Have you tried both? I'm just figuring that it shouldn't be that hard to make them work, because they use the same processor and hardware setup as most of the Civics and Integras from 88-91.

[carotman]

The PK2 and PH3 roms should be virtually the same. They aren't readable by the easy editors out there.

My goal here is to get the 88-89 PH3 rom BIN and import it in a PK2 ECU. Add the necessary hardware mods and see how it runs. This would solve the ECU problem for all those B20A swaps out there. You would get the proper ECU without a hassle.

[Kabuki]

Well, If that works, I'll have a PK2 ECU up for sale, once I get around to it. I'm going to use my PM8 in the project Lude instead of the PK2, so I'll let you all know.

[carotman]

Ant what distributor are you planning to use with the PM8? Also, this ECU lacks an external rom and is a bit trickier to chip.

[Kabuki]

Ant what distributor are you planning to use with the PM8? Also, this ECU lacks an external rom and is a bit trickier to chip.

Uh... Not really sure... I have lots, so, that's not much of an issue. I was thinking that I may use my P07, too... But then I'm going OBD1. It would be nice for tuning, since the P07 has the built in wideband oxygen sensor controller... :D But we'll see... I need to actually build the engine first... And the CR-X has to be finished before I even start on the 2nd Lude.

[carotman]

Well, I desoldered the ROM on the ECU today. I'll go to the local electronic store and see if they can extract the BIN out of it. Hopefully it's not damaged.

[Kabuki]

Otherwise you can send it to me... I'd be happy to. I'd even make a copy on another chip and send them both back to you... :D

[carotman]

Well, today I installed an IC socket on the ECU and powered it with 12V. I didn't get a solid CEL so this is good news!!

This means I successfuly desoldered the ROM. I will try to read it with the ROM burner I ordered last week. I hope everything goes as planned :D

[thegreatdane]

Do I see a PH3/PK2 rom editor coming? :D
Better freshen up those hex editor skills carotman :)

[carotman]

Well, I got my chip burner today and extracted the ROM. It seems complete but when the ECU is powered by this ROM, I only get a code 15 (Ignition) and that's all so I don't know what to do now. I compared it with another ROM that I had found on the net and it is a bit different.

I Put a PK2 ROM in this ECU and is seems to work good. I get the Code 15 and a bunch of other codes so this means it actually works. I will try to put the PH3 rom I found on the net in my ECU to see if the one I extracted is good or not.

This is getting better and better!

Here's the ROM I extracted in case someone wants to look at it.
My PH3 bin

And here's the one I found on the Net. I have yet to try it in the ECU
Unknown PH3 Bincd ..

[carotman]

I disassembled both roms and started to compare them. So far Both PH3 roms I got seem to have the same assembler code. The one I desoldered was from an auto car supposedly but it shouldn't pose too much problem. I will compare them to a PK2 and see if there's any difference between those.

God I love this!

[nswst8]

Thanks, for all your persistance and hard work. I, for one do appreciate your efforts.

[carotman]

Thanks. This is quite some work to do all this and it's only the beggining. This is mostly for personal information since not many members have a B20A engine. However, this will benefit the whole B20A community (including the 3G lude) if I finally find something.

Oh, BTW, I finally compared both PH3 roms I had and it turns out they are totally the same. Mine came from an auto and the other one is from an unknown source so I have yet to confirm the Auto and manuals are the same or not.

At least this means I'm on a good track

I compared the a OzDM PK2 ECU bin I got on PGM-fi.org and the assemble code has some differences with the PH3 (that was expected). I compared what I thought to be the fuel tables and they are located in the same place in the ROM so this is good news. The values are a bit different too but not too much. I will have to compare this with a Canadian PK2 I will get at the junkyard.

I still need to understand how those maps work but I'm sure I'll work something out.

[carotman]

Ok, I got the fuel maps

The PH3 and PK2 share the SAME fuel mal design. They seem to be very different than the other OBD-0 and OBD-1 setups I've seen.

I noticed that there are four 20X16 tables beggining at adress 5900h
There are two 11X17 tables at 5DF5h
There are two 20X4 tables at 5FA0h

The usual OBD-0 uses 15X17 tables and OBD-1 uses 10X20 so I don't know that this means yet.

However, this DO mean that you can put the PH3 fuel maps in the PK2 ecu and run your B20A up to it's original specs. (with 2 O2 sensors however)

[smufguy]

its the diode on Q21 slot right? thats the only thing i could differentiate.

[Kabuki]

Wow, good work so far! If you didn't know, the source code for TurboEdit has been made available to the PGMFI.org community, so that would be a great place to start. You may just need to change the table sizes and locations to match the PK2/PH3 ROMs.

[carotman]

Sweet!

I will need help on the Tables setup for sure. Feel free to contribute :p

However. Those maps seem to be wayyy different that the others I've seen on pgmfi.org. I still can't figure out what they do The other maps have a column multiplier but these don't seem to have one :(. Maybe they are just 16 bit tables (10X13) with no multiplier

This still doesn't explain why there are 4 of those tables.

Smufguy: diode A21 huh? I'll have to look into this.

[smufguy]

it was a typo jean. its q21

[Kabuki]

This still doesn't explain why there are 4 of those tables.

It has VTEC! No, wait... It could... But probably not...