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Artifex · 09-20-2006, 08:27 PM

OBD2 Compliance
The 2nd big domain is OBD2 compliance. If your Honda is younger than 1996, this doesn't apply to you. This is a concern in many states, and the number of states adopting OBD2 testing grows every year. If you don't have to get OBD2 tested this year, you may end up needing this next year, so don't discount OBD2 automatically. OBD2 is a technology mandated by the government, to improve the early detection of electrical and mechanical problems in the car. The Engine Control Unit (ECU) provides this feature. Overall, this technology is very useful, but it presents issues for the performance aftermarket.

This is a problem, because any real aftermarket ECU for Hondas don't provide OBD2 compliance. The most popular ECU mod is a conversion to OBD1 (which is programmable), which clearly means that OBD2 capability is lost. Other high quality standalones (AEM EMS, Autronic) don't support it, and have no intention of supporting it. Therefore, this is a big concern when upgrading the ECU.

There are some ECU upgrades which keep your original ECU, and these are known as piggybacks. These devices generally make less power, but they are easier for end users to install. Using one means you can preserve the OBD2 feature of your stock ECU. It is also worth adding here that there used to be a lot of discussion here about the "OBD2 workaround" (the original text was taken down). It is important to note that the workaround is not reccomended anymore, because it messes with the LTFT settings. The "workaround" also messes up the driving cycle, which is a test that the ECU does after it has been reset. The driving cycle is a small period of time it takes for the ECU to measure all the sensors, and set all the ready codes. On the Prelude ECU, this takes about an hour. Not hard to do for an annual inspection.

The basic premise of OBD2 testing is that officials will plug in special scanning equipment into the OBD2 port of your car. They will read out information stored in the ECU, and make sure the ECU doesn't indicate any error conditions or warnings. For the most part, the emissions techs rely exclusively on the data coming back from the ECU. If the ECU says everything is kosher, the tech will sign off.

So the real question is: how to we provide an OBD2 data port for the techs? There are 2 ways to do this. The first is not common, so I'll only mention it briefly. You can run a newer OBD2 ECU, which are programmable (Flash-based). This only applies to cars newer than 01, so it usually won't apply. One solution I haven't yet seen is to adapt a newer 01+ ECU to run an older motor. Theoretically it can be done, but I haven't seen this yet. The other more feasible solution is to run the original ECU during the short time the car is in for smog testing. This works, but you have to be very careful about how you do it.

For an N/A car, it's relatively easy. Even with some extensive N/A mods, the car will run on the stock ECU. The stock ECU will control injectors up to 20% larger with the proper learning. The key factor here is to keep the care in closed-loop when driving. On a Prelude ECU, this means keeping the throttle under 33% open, and keeping the RPMs under 4000. This forces the ECU to use the O2 sensor to keep the AFRs around stoich, which will mean the ECU will compensate for any intake/exhaust flow differences (or anything else).

For F/I cars, this can still work. The biggest issue is how to handle the fuel system. If your injectors are more than 25% larger (nearly always true), then the stock ECU won't be able to handle them. The simplest solution is to put back the OEM injectors to get smogged. Make sure to install the original ECU at the same time. The second key to making this work is to keep the car out of boost. For turbo cars, this means forcing the wastegate open all the time. This can be done with a length of bailing wire, available at Home Depot. Just wire the wastegate arm all the way open, and the turbo should stay off boost. For external wastegate, there should be a way to do it, but I don't know it offhand. For a supercharger, there should be a way to force the bypass valve open all the time. If that isn't practical, you can also take the drive belt off.

The last thing to remember is to complete the driving cycle.

09-20-2006, 08:27 PM	#2 (permalink)
Artifex Retired PO Adminsicle Join Date: Jun 2002 Location: San Jose, CA Posts: 2,517 iTrader: (0)	OBD2 Compliance The 2nd big domain is OBD2 compliance. If your Honda is younger than 1996, this doesn't apply to you. This is a concern in many states, and the number of states adopting OBD2 testing grows every year. If you don't have to get OBD2 tested this year, you may end up needing this next year, so don't discount OBD2 automatically. OBD2 is a technology mandated by the government, to improve the early detection of electrical and mechanical problems in the car. The Engine Control Unit (ECU) provides this feature. Overall, this technology is very useful, but it presents issues for the performance aftermarket. This is a problem, because any real aftermarket ECU for Hondas don't provide OBD2 compliance. The most popular ECU mod is a conversion to OBD1 (which is programmable), which clearly means that OBD2 capability is lost. Other high quality standalones (AEM EMS, Autronic) don't support it, and have no intention of supporting it. Therefore, this is a big concern when upgrading the ECU. There are some ECU upgrades which keep your original ECU, and these are known as piggybacks. These devices generally make less power, but they are easier for end users to install. Using one means you can preserve the OBD2 feature of your stock ECU. It is also worth adding here that there used to be a lot of discussion here about the "OBD2 workaround" (the original text was taken down). It is important to note that the workaround is not reccomended anymore, because it messes with the LTFT settings. The "workaround" also messes up the driving cycle, which is a test that the ECU does after it has been reset. The driving cycle is a small period of time it takes for the ECU to measure all the sensors, and set all the ready codes. On the Prelude ECU, this takes about an hour. Not hard to do for an annual inspection. The basic premise of OBD2 testing is that officials will plug in special scanning equipment into the OBD2 port of your car. They will read out information stored in the ECU, and make sure the ECU doesn't indicate any error conditions or warnings. For the most part, the emissions techs rely exclusively on the data coming back from the ECU. If the ECU says everything is kosher, the tech will sign off. So the real question is: how to we provide an OBD2 data port for the techs? There are 2 ways to do this. The first is not common, so I'll only mention it briefly. You can run a newer OBD2 ECU, which are programmable (Flash-based). This only applies to cars newer than 01, so it usually won't apply. One solution I haven't yet seen is to adapt a newer 01+ ECU to run an older motor. Theoretically it can be done, but I haven't seen this yet. The other more feasible solution is to run the original ECU during the short time the car is in for smog testing. This works, but you have to be very careful about how you do it. For an N/A car, it's relatively easy. Even with some extensive N/A mods, the car will run on the stock ECU. The stock ECU will control injectors up to 20% larger with the proper learning. The key factor here is to keep the care in closed-loop when driving. On a Prelude ECU, this means keeping the throttle under 33% open, and keeping the RPMs under 4000. This forces the ECU to use the O2 sensor to keep the AFRs around stoich, which will mean the ECU will compensate for any intake/exhaust flow differences (or anything else). For F/I cars, this can still work. The biggest issue is how to handle the fuel system. If your injectors are more than 25% larger (nearly always true), then the stock ECU won't be able to handle them. The simplest solution is to put back the OEM injectors to get smogged. Make sure to install the original ECU at the same time. The second key to making this work is to keep the car out of boost. For turbo cars, this means forcing the wastegate open all the time. This can be done with a length of bailing wire, available at Home Depot. Just wire the wastegate arm all the way open, and the turbo should stay off boost. For external wastegate, there should be a way to do it, but I don't know it offhand. For a supercharger, there should be a way to force the bypass valve open all the time. If that isn't practical, you can also take the drive belt off. The last thing to remember is to complete the driving cycle. __________________ Ken I am no longer an active member of the moderation team. Please contact another mod if you need help with anything. 2000 Base Prelude RIP Pics of Jessica Alba naked! Last edited by Artifex : 09-21-2006 at 01:30 PM.