When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've been having trouble passing emissions and wondering if anyone has advice. The car is a RHD 1995 Type RB and has all of the original emissions equipment on it. So far, I have verified that the air pump is working, cleaned out the catch tank under the throttle body, new spark plugs, air filter, and o2 sensor. It might just be the cat, but I don't really want to drop $1800 on a new one unless I am sure. With that in mind, if anyone knows of direct fit aftermarket cats that could still pass and cheaper than the oem one, that would be helpful to know too. I am not worried about the visual inspection as every time I have gotten it tested, they look at the DR2365 vehicle evaluation form I got from the state and don't do the inspection themselves. I'll attach a few of the test results I have, the most recent one failed with HC at 2.9861 GPM with a limit of 1.2 and CO at 44.977 with a limit of 15. NOx is consistently below the limit.
JDM cat probably did not have the same precious metal loading as US market as the exhaust emissions standards were much less stringent. It might be that a JDM cat may not be good enough. Add to that, the IM 240 cycle is hard for FD’s as the driver gets into the throttle on the accels and the car gets into boost. Real careful test cycle driving is mandatory and likely a good working US-spec main cat, also.
Having helped several people with this issue, it is highly likely too much boost or just the driving style of the tester. I'm assuming nothing has completely failed emission equipment wise. Is the car 100% stock? Boost increased at all?
You are failing CO and HC. CO especially is associated with a rich mixture. Your main CO spikes are at 90 seconds and 150 seconds in the above chart. There's a little bit of a time delay for the emission analyzers to show the spike, but see how it not only spikes up but it's "Square" looking? That means it's pegged the range of the chart, if not the analyzer itself. Notice those are two heavy accelerations.
Tell the tester to take it easy in the way he drives it.
Cats do very little for CO under heavy acceleration because all that air and fuel just blows right through the cat. Cats mostly control CO under low load closed loop conditions, if the O2 sensor is working correctly to adjust the air fuel ratio to allow oxidation reactions. Main driver of CO (and HC to an extent) under heavy acceleration is air fuel ratio, which depends on engine load (here rpm and boost) and the tuning of the ECU (here tuned by Mazda with at least some consideration of emissions, but emission standards were not very strict back then).
May also be worth loosening an intercooler coupler clamp so the car doesn't get into boost, that may help things. I don't have any experience actually passing emissions tests though.
I have also read that having the car HOT when you take it to the test helps a great deal. Like go beat on it and take it to the test. A good, hot engine and cat work best.
Having it warmed up with a hot cat will help, but the biggest spikes in emissions are appearing on the second portion of the test, after 90 seconds. By then the engine and cat have had at least a little time to warm up from however long it was sitting. It's certainly best to drive the car hard before taking it to the emission station, and see if you can get there when it's not busy so the car doesn't have to cool down too much.
OP did you observe how long the vehicle was sitting? Did it sit for a couple hours at the inspection station and then they idled it while moving it on to the chassis dyno rollers?
In addition to the excellent advice above I also recommend that you explore the waiver process as well. Sometimes there is a dollar amount attached to it. So let's say you modify an emissions component to attempt to pass the test, that counts towards the waiver process. Adding a new catalytic converter, re-tuning the engine, replacing solenoids, rebuilding turbos/engine. In MD the bar was pretty low. $450 in receipts for any parts repaired forward of the catalytic converter counted towards the waiver. Since the rules are already skewed against you with a rotary, then exclude you all together with a RHD Car, I suggest it is sometimes better to play the game than get bent over by it.
Having it warmed up with a hot cat will help, but the biggest spikes in emissions are appearing on the second portion of the test, after 90 seconds. By then the engine and cat have had at least a little time to warm up from however long it was sitting. It's certainly best to drive the car hard before taking it to the emission station, and see if you can get there when it's not busy so the car doesn't have to cool down too much.
OP did you observe how long the vehicle was sitting? Did it sit for a couple hours at the inspection station and then they idled it while moving it on to the chassis dyno rollers?
I drove it pretty hard for about 45 minutes before the test, then sat there idling while 2 cars went before me. They turned it off when they checked the gas cap but that was very brief so I find it hard to believe the car cooled down much at all.
In addition to the excellent advice above I also recommend that you explore the waiver process as well. Sometimes there is a dollar amount attached to it. So let's say you modify an emissions component to attempt to pass the test, that counts towards the waiver process. Adding a new catalytic converter, re-tuning the engine, replacing solenoids, rebuilding turbos/engine. In MD the bar was pretty low. $450 in receipts for any parts repaired forward of the catalytic converter counted towards the waiver. Since the rules are already skewed against you with a rotary, then exclude you all together with a RHD Car, I suggest it is sometimes better to play the game than get bent over by it.
Tried that... I spent the $715 required here in CO only to be told later on that they won't give out waivers to grey market vehicles.
May also be worth loosening an intercooler coupler clamp so the car doesn't get into boost, that may help things. I don't have any experience actually passing emissions tests though.
I have also read that having the car HOT when you take it to the test helps a great deal. Like go beat on it and take it to the test. A good, hot engine and cat work best.
Dale
I've thought about loosening an intercooler hose for that reason, but was unsure of the effect it would have on the turbos
I've thought about loosening an intercooler hose for that reason, but was unsure of the effect it would have on the turbos
Long term that wouldn't be a good idea, but for the test it's fine.
Had a buddy's car once with the clamp just loose, visually looked perfect. Literally had no boost, like driving a non-turbo RX-7 2nd gen, didn't even make funny noises. Again, I've never had to deal with emissions testing but that makes sense to keep the car out of boost and out of the super rich fuel map.
If you can disconnect/cap off the precontrol and wastegate air hoses, that will lower the boost. I think you will get a check engine light if you actually unplug the solenoids. Basically that will put you at wastegate spring pressure.
Took it in for another test today with the intercooler hose clamp loose and therefore no boost. The numbers were the same though, which I don't understand
This might be completely off-base, but Japanese FDs don't have the pre-cat like North American models. I would wager that presence/absence of this would have an effect on CO/HC emissions. Give me a few minutes and I'll post the Japanese emission numbers straight from the Workshop Manual.
From the 11/1991 Workshop Manual, Page A-35
Test Conditions: At Idle (700-750rpm)
CO Concentration: 0.4% or less
HC Concentration: 90ppm or less
This covers every Japanese FD ever made. Also, both the FC and JC Cosmo emissions are the same too as all 3 conform to the Emission Standards and Shaken regulations effective for Showa 61 (1986).
Last edited by Akagis_white_comet; 11-03-21 at 04:21 PM.
Reason: Original CO/HC emission specifications
10-26-21, 01:16 PM
