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obd0 or obd1

 
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Old 08-17-2015, 02:58 PM
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obd0 or obd1

Curious if there's really a difference. You still have to count the blinks , Right? Why is it different and why did Honda decide to have both during the same year?
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Old 08-17-2015, 05:06 PM
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Re: obd0 or obd1

Yes, there really is a difference. Besides the obvious difference of OBD1 being for the b21a1 and OBD0 for the b20a5, one big difference is that if you are swapping in an h22, with OBD0 (b20a5) you need an OBD0 to OBD1 conversion harness, with OBD1 (b21a1) you obviously don't because it's already OBD1. Also, OBD1 shows a couple codes that OBD0 doesn't show (41 and 43). From what I've read (I don't have first-hand knowledge of this) you can normally tune OBD1, but not OBD0. But for some reason Honda made the 3rd gen Prelude OBD1 ecu (PK3) such that it isn't tunable.
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Old 08-17-2015, 05:20 PM
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Re: obd0 or obd1

The prelude models, or really any Honda models that are more advanced or featured than the rest of the manufacturer line, are essentially testing grounds for up coming advancements in design thoughts. For example the 4WS, ALB, multiplex body control systems, FRM cylinder walls, IAB's and OBD1 are just some of the things tested on the 3rd gen preludes before either going into full line production, or just being passed by. While OBD1 was under development in the late 80's, and first tested in production in the 90-91 usdm b21a1 preludes, the rest of the Honda line didn't see OBD1 until 92. On all other Honda's, the OBD0 distributors used a 16 tooth CKP rotor. Model year 88+ fuel injected preludes and all other 92+ Honda's use a more refined 24 tooth CKP rotor. The reason the 3rd gen preludes all used a 24 tooth CKP rotor is because even though the PK2's came in what looks like an OBD0 ecu, it used basic OBD1 micro processors, coding, and serial protocol. So even the PK2 is basically an OBD1 with OBD0 connectors. The PK2's and OBD1 honda ecu's used intel based micro processors manufactured by OKI Processors LTD, so I guess you could say our cars had "intel inside" before it was cool.

The main differences between OBD0 and OBD1 from a stock standpoint is the OBD1 ecu's supported engine data pid monitoring through a 3pin DLC. This DLC used a TX-RX format referred to as half-duplexing resulting in slow communication. This means it used a single line for both the TX and RX meaning the transmitted data(TX) and received data(RX) only used one wire so the scan tool had to wait for an answer before it could ask its next question, similar to but slower than the K-line found in early OBD2 communications. The other two wires of the DLC were there to supply power/ground to the scan tool.

From an aftermarket standpoint, both ecu's support engine data pids through a header connector you must install at location CN3 inside the ecu. With this header in place there is a jumper resistor you need to remove, then the ecu supports Full-duplexing. This results in much faster data transmissions because the ecu and data logger tool(freelog, crome pro, neptune, hondadata for example) can both speak at the same time on their own channel. Many people prefer OBD1 because they can use a OBD1 civic/integra ecu which has heavy aftermarket support for tuning and modifications. The reality is any ecu is tune-able but the civic/integra's have options for rom editors so people without the knowledge can modify easily.

Unfortunately for many, the PK2/PK3 lines of ECU's are not supported by any rom editor applications... kind of. I have done some development of support for the PK2 although limited and have written a mask program for tunerpro RT to aid in editing. I have disassembled several roms for the PK2 and have the ability to change fuel and ignition tables, and correct the check sum routine for modifications. I am now looking at egr control and hope to get to rev control next. I also have a one off rewritten version of turbo edit that has limited support of the PK2. everything I have on this is free for anyone interested, just ask and you shall receive, or I can also just do the editing for you.

This may have been more of an answer than you expected, but if it raised more questions of failed to answer yours in a suitable manner just let me know and I will address it accordingly.
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Old 08-17-2015, 07:46 PM
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Re: obd0 or obd1

^^Wow! Thanks for the history/engineering lesson.

Learning is fun.
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Old 08-18-2015, 10:33 AM
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Re: obd0 or obd1

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Originally Posted by luda8890 View Post
The prelude models, or really any Honda models that are more advanced or featured than the rest of the manufacturer line, are essentially testing grounds for up coming advancements in design thoughts. For example the 4WS, ALB, multiplex body control systems, FRM cylinder walls, IAB's and OBD1 are just some of the things tested on the 3rd gen preludes before either going into full line production, or just being passed by. While OBD1 was under development in the late 80's, and first tested in production in the 90-91 usdm b21a1 preludes, the rest of the Honda line didn't see OBD1 until 92. On all other Honda's, the OBD0 distributors used a 16 tooth CKP rotor. Model year 88+ fuel injected preludes and all other 92+ Honda's use a more refined 24 tooth CKP rotor. The reason the 3rd gen preludes all used a 24 tooth CKP rotor is because even though the PK2's came in what looks like an OBD0 ecu, it used basic OBD1 micro processors, coding, and serial protocol. So even the PK2 is basically an OBD1 with OBD0 connectors. The PK2's and OBD1 honda ecu's used intel based micro processors manufactured by OKI Processors LTD, so I guess you could say our cars had "intel inside" before it was cool.

The main differences between OBD0 and OBD1 from a stock standpoint is the OBD1 ecu's supported engine data pid monitoring through a 3pin DLC. This DLC used a TX-RX format referred to as half-duplexing resulting in slow communication. This means it used a single line for both the TX and RX meaning the transmitted data(TX) and received data(RX) only used one wire so the scan tool had to wait for an answer before it could ask its next question, similar to but slower than the K-line found in early OBD2 communications. The other two wires of the DLC were there to supply power/ground to the scan tool.

From an aftermarket standpoint, both ecu's support engine data pids through a header connector you must install at location CN3 inside the ecu. With this header in place there is a jumper resistor you need to remove, then the ecu supports Full-duplexing. This results in much faster data transmissions because the ecu and data logger tool(freelog, crome pro, neptune, hondadata for example) can both speak at the same time on their own channel. Many people prefer OBD1 because they can use a OBD1 civic/integra ecu which has heavy aftermarket support for tuning and modifications. The reality is any ecu is tune-able but the civic/integra's have options for rom editors so people without the knowledge can modify easily.

Unfortunately for many, the PK2/PK3 lines of ECU's are not supported by any rom editor applications... kind of. I have done some development of support for the PK2 although limited and have written a mask program for tunerpro RT to aid in editing. I have disassembled several roms for the PK2 and have the ability to change fuel and ignition tables, and correct the check sum routine for modifications. I am now looking at egr control and hope to get to rev control next. I also have a one off rewritten version of turbo edit that has limited support of the PK2. everything I have on this is free for anyone interested, just ask and you shall receive, or I can also just do the editing for you.

This may have been more of an answer than you expected, but if it raised more questions of failed to answer yours in a suitable manner just let me know and I will address it accordingly.
WOW! That is some pretty in depth information! I am impressed! (Not that I doubted or anything) REP given!
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Old 08-18-2015, 03:32 PM
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Re: obd0 or obd1

Amen brother!
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Old 08-18-2015, 03:40 PM
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Re: obd0 or obd1

I certainly learned something. It's good to know that there are still people with your knowledge and abilities who are willing to help other 3rd gen owners out without taking people's money. Thanks for the thorough explanation!
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Old 08-18-2015, 10:52 PM
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Re: obd0 or obd1

Thank you guys, I was trying to give a decent answer. Something better than the usual "obd1 is better" opinion.
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Old 08-19-2015, 11:06 AM
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Re: obd0 or obd1

Sounds like you designed it yourself... Modesty is kool...
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