CA smog check after engine rebuild tips?

[JonsE30]

trying to prepare for a smog check after my m42 rebuild. are there any steps to put me in the best position to pass? i did the mess under the intake cleanup but i think i read somwhere that it shouldn't affect smog. i don't have any check engine lights. i maybe have only 2 miles on the engine since it's first start. i already did a fuel filter change, cleaned out ICV, etc. do i need to drive it a certain amount of miles for it to "re-learn"? i'll also do the fresh oil and filter change prior.

i have about 1/4 tank of 2 year old gas which i am guessing i want to get that out of there and put fresh new 91 gas in there?

[roguetoaster]

No learning to worry about, but I'd think 200 to 500 miles of driving before testing would b3 best, which would solve the poor fuel issue too. The condition of the O2 sensor and catalyst will also be critical to testing, so consider how old those are.

[bmwman91]

The long term fuel trims from O2 feedback should be settled after 20 minutes of being fully warmed up and driving normally. Data logging I have done in the past shows the adaptation being close to 90% done after just 5 minutes.

Passing CA SMOG is dead simple if you have a working O2 sensor, no large vacuum leaks and functioning catalytic converter. 95% of the people on here saying that they are failing and looking for gimmicks to pass (red-line it around the block first, gas additives, unplugging the O2 sensor, etc) have a crapped out catalytic converter and refuse to spend $250 on a replacement. The stock cat is not CA legal so you can't waste $500+ on one of those even if you want to, but most shops will be perfectly happy to sell you (and weld in) a CA-legal Magnaflow unit for under $300. I've done that twice in the last decade and passed SMOG with flying colors every single time...near-zero emissions on the print-out, with no hard driving or any other extra warm-up measures beyond the tech letting it idle for 10 minutes as he checked the evap system for leaks before doing the sniffer test. Those passes were also with a 2.1L fully built M42 with nearly 12:1 compression and hot cams.


If your car still has the original cat and was having trouble passing 2 years ago then maybe you should think about replacing it. Otherwise just go take the test, and if it fails get a new cat welded in and you are guaranteed to pass if everything else is in working order. Again, most of the people on car forums lamenting how "difficult" the CA SMOG test is have spent all sorts of money on mods while being too cheap to maintain the few items that matter for SMOG.

[JonsE30]

when i got smogged 2 years ago, the tech saw the odometer said no way it will pass and to his shock it passed just fine. i havent touched the o2 sensor other than unplugging it before i took the engine out for its rebuild. i dont think i have any major vacuum leaks. will it do any harm to the engine to drive around to use up that 1/4 tank of old gas?

[bmwman91]

Nah, just don't redline it if you think there is water in there. Go use that stuff up and refill it. If you are really paranoid, you can unhook the fuel filter, jump the fuel pump relay and pump it all out into a bucket or something. It's probably fine either way.

[roguetoaster]

Always better to remove old fuel rather than use it, but if you do use it be sure to keep the RPM low until after you refill. Remember, $20 worth of discarded fuel just isn't worth economizing over relative to anything going wrong.