This is exerpted (is that a word?) from NPOG:

"There has been much debate over how OBD2 ('96 and up Preludes) works and what it does. What is known to the tuning world from dyno plots and tuning is that the ECU on OBD2- equipped vehicles will eventually "detune" modifications that alter cam timing, ignition timing, and air/fuel delivery. This includes common breathing modifications (intake/header/exhaust and port work). What this means for the average tuner is that when you bolt on i/h/e, do manifold or head (port) work, change injectors or fuel pressure, or just about any other engine-related mod, the ECU will detect the change in emissions and alter the timing and fuel maps to compensate. This has been dyno proven on multiple occasions with multiple different performance mods. It also happens that this is especially true for air/fuel controllers (AFCs). "

What do you guys who have any engine mods done do as a workaround for this? The site lists several options, as cheap as pulling the fuse and letting the system reset every few days, up to suggesting something like an AEM ecu.

If you were to go the route of an aftermarket ecu, or even just a reprogrammed stock one, what happens when inspection season rolls around? (here in NY, the inspection station hooks the car up to a computer, etc etc...)

 

OBD-II is not easy to override without an external device. In states like NY and PA-inspection depends on readings taken from a STOCK ECU for 96 and up cars made by most companies. That is one reason that the connector is now universal and the test fee so high. The old-up the pipe method-may be used in other places, but in our cases poses a serious dilemna. What can you do-very little. The fact is that there is an effort afoot to make it extremely difficult to modify a car-even if the result is better than stock. Go figure.
Simnple answer is the most difficult achieve-move to somewhere that does not have strict emissions tests. Sadly, even that is coming to an end as the Fed imposes rules that are connect to highway funding dollars.

 

That does suck. I know lots of mods seem to maintain road legality (headers that still accept sensors, etc), but if the benefits of these things are overrided by the stock ecu later on anyhow....

So I guess the priciest option is: do your mods within reason, get an aftermarket ecu, get the car tuned correctly with that, and then switch ecu's and limp to the inspection station annually.

 

I've got a 99 type sh all motor build. I put down 193.5hp 155ftlbs torque on an obd2 ecu and a vafc . I've got Je forged pistons, eagle H -beam forged rods, crower stage 2 cams, tit retainers, dual vs, ss valves and so forth. I did the workaround mod and the car was dynoed on a mustang dyno 1100se on a 93 degree day with 65% humidity. On a 70 degree day with low humidity the tuner said it would've made 205 to the wheels. My air fuel hasn't ever been leaner than 12.6 and spends most of it's time in the 10's and 11's. This is with the timing belt off/cam timing off also. You can make power on obd2 I'm tellin ya. I'm going ultimate emanage and greddy E-01 controller to retain the atts. This is in a 3000+lb full interior type sh that they computed 3375lbs as the weight into their dyno and the cars at least 170 lbs lighter with me in it!

 

hmm well i got an intake and a custom done header with 2.5" collector and 2.5" all the way back to the muffler......im planning on gettin skunk2 stage1 cams and a new intake manifold and a vtec controller.....wud i need to do a workaround to benefit from these mods or are they not enuf for a workaround to be worth it

 

http://www.ntpog.org/mods/fifth-afc/ecu.shtml
this site will solve all your problems and any questions you may have had.
also it has other nifty how too's as well.