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Emissions & Modifying your car

32813 Views 43 Replies 21 Participants Last post by  fb6ben
OK this has been coming up an excessive amount of time. First thing's first:

- If you're worried about passing emissions, do not modify your car.

Tuning solutions (FlashPro included) are sold as "OFF ROAD USE ONLY" products, meaning they are not there to help you pass emissions, fudge your emissions, or in any way let you sneak through emissions testing with a modified vehicle. In fact, it's illegal. It's actually illegal for anyone to even try and help you fudge any emissions testing -- there are federal and state regulations regarding emissions equipment & testing. So, having "tuning' won't guarantee you will pass emissions, but also does not guarantee you will fail emissions -- the simple fact is don't expect the "tuning" to let you pass emissions just because you "tuned" it.

But hey, we're going to modify our vehicles, so how do we pass emissions and readiness tests?

It's very simple, as long as all your factory emissions equipment is working EXACTLY like stock, readiness will set, and if that is what your emissions test requires, you will pass.

Now what do I mean by exactly like stock? This means everything on the car, primary o2 sensor, secondary O2 sensor, EVAP system, etc, all work, are all *enabled*, and none of the codes these systems throw when they find a fault are disabled in the map. If the codes are disabled, the ECU will *NOT* set the readiness. Another fun fact, is EVAP readiness typically will *not* set until the catalyst system sets. So even if you have everything *but* the catalyst tests (secondary O2 sensor off or throwing codes due to HFC/downpipes/headers) working right, you may still have 2 systems that will not set readiness.

By default we disable the secondary O2 sensor in tunes because it *will* apply trims that screw up the mapping (particularly on vehicles with aftermarket downpipes). Modern ECU's use a wideband front O2 sensor, and the narrowband secondary O2 sensor as a sanity check for lean/rich conditions. When you change the downpipe to use an aftermarket cat or no cat at all, that reading is now SKEWED and not reliable.

In conclusion, it is not humanly possible for us to keep up with all the various state emissions regulations -- this is up to you. If you're worried about emissions and want a fast car, my recommendation is to buy a Corvette, Mustang or GTR. If you are modifying a car and are able to pass emissions still, awesome, let's build a fast car. If you're modifying a car and aren't worried about emissions, hell yeah, let's build a race car?
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What would happen if you were to temporarily enable the secondary o2 sensor come inspection time? Would the car still be drivable (maybe with an emissions tune) and pass emissions? Im going to run a cat but just need all emissions to set ready for the obdII scan.
Would like to know this as well. My mods are small so going back to the stock tune for smog wouldn't be an issue at all. Just as long as I can do that for smog and the car would pass readiness I would be happy.
Same here, from my understanding by disabling the secondary o2 sensor your monitors wont set ready and disabling it is the standard when having your car tuned.
This is a big deal to me cause I dont want to start modding my car if im not gonna be able to pass emissions.
Hopefully enabling the secondary o2 sensor a week or so before inspection and doing lots of driving will allow the readiness monitors to set. I have inspection coming up at the end of the year and am gonna have to try this or return to stock.

Anyone have success with doing what I'm talking about or am I in for a surprise?
Can someone tell me how to go back to the stock tune? I cant pass inspection and im currently about halfway done with getting tuned by Vit, so I assume that has something to do with it. The mechanic said I just needed to perform a drivecycle but ive driven 300 miles and it still wont pass. So I figure going back to stock for a week or so should do the trick!
There's an option to unlock flashpro and return the car to stock. I can't think of where it is off the top of my head but its in there somewhere.

Plug flashpro into your pc and open flashpro manager, go to the online drop down menu towards the top left. The option to return ecu to stock and unlock flashpro from the vehicle are here. I assume you return the ecu to factory before unlocking it from the vehicle. Not sure of the exact sequence but im sure at some point you will have to plug flashpro into the car to flash it back to factory.
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