Getting Ready for CA Emissions!
 

Hey, I’m wrapping up a full engine rebuild with my son for his 1993 FD. We’ve taken as much as we can back to stock with all new hoses and seals, and are looking to put it through California emissions testing once running. I bought a second-hand stock cat and pre-cat downpipe to replace the PO’s straight downpipe and high flow exhaust. We also installed ACV, air pump, and EGR.
For computers we have PFC and stock, and I added a connector to quickly switch between wiring configurations for the two.

I have two questions.

First, is it correct to use the stock computer for emissions testing? As I understand the PFC is pretty naive with how it uses the air pump and ACV, and can’t control the EGR. I’m also not sure if the tune for a modded car would be safe in stock configuration.

Second, should we use the pre-cat or.a straight downpipe? The pre-cat has some damage to the honeycomb which makes me a bit nervous. It has a little rattle if you shake aggressively, and boroscope from the engine side shows the honeycomb is clean, but has partially separated in the middle and around one edge, lifting by about 1/8 of an inch (other side of pre-cat and main cat look in good condition). I’m not sure if a straight downpipe would be safe with the stock computer given potential boost creep (we don’t currently have a boost gauge), and may not be okay for emissions. Perhaps I need to buy new downpipe, or maybe get it re-cored?

We’re pretty new to this and any advice is much appreciated! Here’s a couple pics from the boroscope looking at the cracked edge of the pre-cat:

https://cimg4.ibsrv.net/gimg/www.rx7...afdceaa5f.jpeg
https://cimg5.ibsrv.net/gimg/www.rx7...bb8ce34ce.jpeg

Walter

Downpipe is fine with a factory cat with stock computer as long as you have the factory main cat and not a high flow. You may still want to run the damaged pre-cat so long as it isn't blocking flow just for the sniffer test, then replace with the downpipe after the test, you will have a better shot at passing. You can pass with a downpipe and the stock main cat as long as everything is running great. It has been done. As far as the ECU goes, run the stock. It will most likely fail on the Tune of the PowerFC unless it has been specifically tuned for an emissions run or just really well overall. Most tunes are on the richer side of stock and aren't geared towards passing emissions. I would not run that pre-cat any longer than you have to for emissions purposes, replacing those with a downpipe is now known as a reliability mod because of the heat they keep in and if they do plug up, then its going to do more damage.

Woot - thank you, sounds like good advice, and means we can get bolted up right away without having to track down more parts. Fingers crossed! Everything is so clean inside and out now I’ve got to think this thing should be able to pass.

I know after the sniffer test my son will probably want to bolt on a high flow main cat for the noise, but I don’t know if there’s a config which can work for both of us. Maybe use the PFC and a high flow main cat which accepts secondary air - really don’t want him stinking up the neighborhood again when he warms up the car in the driveway. :)

Walter

Get a boost controller and tune the powerFC when you add the high flow cat. You will most likely get boost creep when you open up the exhaust. There are still a few high flow cats that can accept air pump but modern cats can do without and keep the stink down.

good luck! for the test you will want to run the stock ECU and the downpipe with the cat.

after you should put a downpipe in it, and the PFC back in

please check if your county has IM240 emissions tests. in that case the vehicle is driven on a special emissions dyno. here is an old thread I helped someone with. It's pretty sensitive to how the driver drives the vehicle. If you fail the emissions test, whether it's IM240 or just one with the vehicle idling/stationary, please take a picture of the failed results and post it. It's key to diagnosing the problem.

If you can make it work with the stock ECU I'd try that first. See if you can schedule a test and have them pull it on quickly so the exhaust is hot, or ask to let it idle before the test for a while. The pre cat is going to help if the engine isn't as warm, but since you said it's possibly damaged you should probably not use it.

Failing emissions: high CO but the ACV checked out - RX7Club.com - Mazda RX7 Forum Failing IM240, many new parts, unsure what to do - RX7Club.com - Mazda RX7 Forum