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View Full Version : JDM B20A ECU revealed (PH3)



carotman
12-16-2005, 11:25 PM
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
12-16-2005, 11:33 PM
Good find... i cant wait to see pics... B20a stuff is htf

carotman
12-17-2005, 09:54 AM
Here's the 88-89 PH3 scan from the ECU I got
JDM 88-89 PH3 (http://carotman.no-ip.com:8888/3geez/ecu/ph3_88_89.jpg)

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 (http://carotman.no-ip.com:8888/3geez/ecu/pk2.jpg) (Thanks to PGM-FI.org)

For your info, here's the 86-87 PH3 ECU posted by thegreatdane
JDM 86-87 PH3 (http://carotman.no-ip.com:8888/3geez/ecu/ph3_86_87.jpg)

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

Kabuki
12-19-2005, 11:50 AM
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
12-19-2005, 12:34 PM
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
12-19-2005, 02:30 PM
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 (http://carotman.no-ip.com:8888/3geez/ecu/ph3_88_89_O2.jpg)

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
12-20-2005, 03:48 PM
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
12-20-2005, 07:46 PM
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
12-20-2005, 10:46 PM
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
12-21-2005, 07:10 AM
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
12-21-2005, 12:25 PM
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
12-21-2005, 01:50 PM
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
12-21-2005, 06:24 PM
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
12-27-2005, 12:02 PM
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
12-27-2005, 02:50 PM
Do I see a PH3/PK2 rom editor coming? :D
Better freshen up those hex editor skills carotman :)

carotman
01-03-2006, 11:12 AM
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 (http://carotman.no-ip.com:8888/3geez/hondabins/PH3-0732-88-89-Accord.bin)

And here's the one I found on the Net. I have yet to try it in the ECU
Unknown PH3 Bin (http://carotman.no-ip.com:8888/3geez/hondabins/PH3-86-88-Accord.bin)cd ..

carotman
01-04-2006, 01:13 PM
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
01-04-2006, 06:08 PM
Thanks, for all your persistance and hard work. I, for one do appreciate your efforts.

carotman
01-04-2006, 09:58 PM
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
01-04-2006, 11:55 PM
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
01-05-2006, 07:55 AM
its the diode on Q21 slot right? thats the only thing i could differentiate.

Kabuki
01-05-2006, 03:18 PM
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
01-05-2006, 05:41 PM
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
01-06-2006, 03:30 AM
it was a typo jean. its q21

Kabuki
01-27-2006, 11:54 PM
This still doesn't explain why there are 4 of those tables.


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

carotman
03-19-2006, 02:18 PM
Ok. I made a ROM image with the PK2 code but PH/ fuel/timing maps.

This means that if people want to swap in a B20A, all they have to do is get a cheap 15 bucks PK2 ecu at the junkyard and use this ROM. I tested it in a B20A5 Prelude and the guy said it gave him a boost in performance.

This is good news :D

The dual O2 sensors is still a problem but converting to a single 4-wire O2 is pretty simple. I'll see if I can just disable the secondary O2 in the ROM.

smufguy
03-19-2006, 05:36 PM
Jean, you are a friggin God. :wave:

carotman
03-21-2006, 11:01 PM
Hehe, I'm doing this for my own good too. I doubt anyone will ever use that ROM in the PK2 for an Accord B20A except me but you never know. There are just too few people with B20A swaps here :(

TWOLOUDNPROUD
03-21-2006, 11:06 PM
Hehe, I'm doing this for my own good too. I doubt anyone will ever use that ROM in the PK2 for an Accord B20A except me but you never know. There are just too few people with B20A swaps here :(
I want one for my B20a:wave:

Versanick
03-23-2006, 11:58 AM
I'll jump on that like white on rice. I NEED it.

carotman
04-02-2006, 08:30 PM
Haha, do you guys have a burner or chipping skills? I could just chip them for you if you want.

Versanick
04-05-2006, 09:28 PM
I don't have skills, but chipping would be badass. Do you mean if I send you my ECU, or do you mean you could send over a chip and we could try to chip it?

carotman
04-05-2006, 10:15 PM
You could do both, it's up to you.

I got a second PH3 ECU here that is different than the one I had (manual instead of auto). I'll see if there are any differences.

Versanick
04-30-2006, 12:14 PM
i want ur ph3!! I would cry if you would sell it to me.

Any luck on disabling the secondary O2 in the ROM? And I assume if using a pk2 ecu that you modify, I'll need the prelude distributor as well?

carotman
05-01-2006, 07:06 AM
The Accord and Prelude distributors are the same.

I'm 100% sure that you can use the PK2 with a second O2 disabled just by using the PH3 ROM. I'll get my Accord out next week so I'll be able to experiment.

In the mean time, I know that the ROM I created for the PK2 works. It uses the PK2 code but has the PH3 fuel maps. it helps a bit but it's not exactly what everyone wants.

Versanick
05-04-2006, 07:38 AM
PH3 and pk2 rev limit both 7200?

ph3 fuel maps would be much better than the a20 maps that I'm running. Of course, with my cams and top end work, even ph3 maps aren't going to be even close anyway.

but i'll take 300rpm where I can get it.

and that's great. I'll have to get that pk2 dizzy instead of the 86-89 teg dizzy I'm using.

thegreatdane
05-04-2006, 07:48 AM
PH3 and pk2 rev limit both 7200?

ph3 fuel maps would be much better than the a20 maps that I'm running. Of course, with my cams and top end work, even ph3 maps aren't going to be even close anyway.

but i'll take 300rpm where I can get it.

and that's great. I'll have to get that pk2 dizzy instead of the 86-89 teg dizzy I'm using.

You dont have the JDM B20A distributor that was originally on the engine?

carotman
05-04-2006, 10:26 AM
The good thing about using the PK2 dizzy is that you can use the USDM cap on the distributor. If not, you're stuck with getting a JDM cap... and wires.

Kabuki
05-04-2006, 04:06 PM
Anyone want to send me an old PH3 JDM distributor cap? Okay, maybe a picture would work too... But I can go through everything I can get my hands on, and maybe find a crossreferenc for you guys.

Versanick
05-13-2006, 07:05 PM
I had to replace that junk dizzy. It was making my tachs spaz out and me not fire properly. I got one from (I forget who on the board here) and it seems to be, just as it was before, an 86-87 teg dizzy. Since the motor ran on an a20 ecu when I got it anyway, it had to use that.

I think I want to go obd1 now. The idea of the pk2 with ph3 maps is fine but I think I realized I need to just jump on the obd1 bandwagon. It loads up so bad that it can barely rev past 4-5krpm while popping and misfiring, until it's been warmed up for an hour. This old stuff isn't worth it.

I think pk2 is a much easier conversion though. I haven't stopped thinking about it.

GL on the dizzy cap

carotman
05-14-2006, 10:59 AM
I could send you an old one. One of the posts are missing. I hope I didn't throw it in the garbage. I might his the local junkyard first and see if I can find something similar.

AccordB20A
05-16-2006, 03:13 AM
complicated shit!

I have an assortment of ECUs lying around here.

what i want to know...
i have owned 2 b20a 2.0Si honda accords....
ones a 1985 and the other 1986.
the 1986 had EGR and the 1985 didnt. does this mean the ECU is diffrent? Because the 1986 accord is now running a a18a carb with no need for the ecu and FI system so i have the computer as a spare..so they must be diffrent..right.... or is it a wiring thing in the wiring loom in the car disabling the EGR error codes.

i ran the 1985 engine in the 1986 acord and got EGR error code....

what am i better off using... 1985 ecu or 1986 or even the prelude ecu???
Does the prelude dizzy affect anything else in how the engines running if i was to use it.

also while im on the subject.. what re the difrences in the b20a5 cams to the b20a ones. what cams are the best for high end power on a JDM b20a..seems i have both i may aswell try and get the best out of my engine.

Kabuki
05-17-2006, 10:50 AM
I am pretty sure that the B20A cams are better than the B20A5. In fact, there are lots of 3G Lude guys that pull out the stock B20A5 cams and install B18A/B or B20B/Z cams, because of the higher lift. Keep in mind, also, that you can use the aftermarket cams designed for the non-VTEC B18 engines.

smufguy
05-17-2006, 01:02 PM
ur talking about B18 camshafts on the B20A head? last time Rob tried that, the shafts were too small to fit on the B20 head.

AccordB20A
05-17-2006, 09:16 PM
SwEEEEEEt

Versanick
05-22-2006, 04:51 PM
I think you guys might be confused. I'm using an 86 integra dizzy with the matching cap and rotor. Why would you need the jdm dizzy cap? If you're using the PH3 dizzy, I can understand. Is that what you mean?

And Carotman, let us know if you have any success raising the rev limit. My plan for the summer is: valve springs + retainers, SAFC, pk2 ecu with PH3 maps (or chipped p75 obd1 project if needed), 8200+ rev limit (8500 would be best, to see what this motor can really do).

My cams stop at 7000 and the car pulls harder and harder through 7k now. These stupid Gude cams are huge and want to see more rpm. EVERYTHING else is done to the motor. I just need springs and retainers, to raise the RPM, and to tune it. If you can make the rev limit on that pk2 be like 8200 or 8500 or anything like that, I will gladly pay you for all your awesome work.

you tha man jean

carotman
05-30-2006, 08:06 PM
Sorry, I missed this post.

I haven't been able to raise the rev limit yet. I might come up with something in the future but it's not 100% sure. I'll need help.

You won't need the JDM cap unless you have the JDM PH3 dizzy (which can be replaced with the PK2 dizzy)

Kabuki
05-30-2006, 09:44 PM
Yeah some of the 3G Prelude guys on PreludePower were asking about the SPEED limiter on the PK2/PH3 codebase. I don't think they really get the concept of ECU tuning...
*Sigh*

bullard123
06-15-2008, 06:36 AM
Bump I enjoyed reading this:)

bullard123
06-15-2008, 02:52 PM
Ok. So I have the PK2 ecu but my problem is the dizzy that I haVe has a square plug-in and the B20A wiring harness has a round plug-in. Do I need to splice the wires (Im trying to avoid doing that0)or can I find another dizzy that has a round plug-in that works with the PK2 ECU? Anyone?

AccordB20A
06-15-2008, 03:57 PM
the colours should be the same if you count and look.

bullard123
06-15-2008, 04:04 PM
the colours should be the same if you count and look.

So that means I can just cut off the old connector and splice a new one on? I was hoping I could find one that just plugs in but if not I'll have to just splice it:)

AccordB20A
06-21-2008, 10:01 PM
i cannot say if the connectors are compatible but if you found the other half of the square plug you might be able to de pin your accord one and put the pins in the right places on the sqaure plug