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Smog issue - high HC at idle

mk2davis

Well-known member
Joined
Mar 1, 2015
Messages
191
Location
Ventura, CA
Many of you have been following my progress, and I appreciate all the help. Today I failed my CA smog test with the following numbers

RPM %CO2 %O2 HC Max HC Meas CO Max CO Meas
Idle 8.0 9.3 120 280 1.00 .14
2500 15.0 .3 140 48 1.00 .17

So at 2500 rpm I'm golden. Idle though.... not good. Smog guy wants me to get a new cat. Before I put down a small pile of money, does anyone else have any suggestions? When I put the new motor in, I replaced all my vacuum lines and torqued down all my IM hardware.

No CEL, car runs really well now that I've replaced my knock sensor. Exhaust does kinda smell "eggy".

All help is appreciated.
 

idreamidrive

Well-known member
Joined
Oct 10, 2012
Messages
430
Location
Murray, KY
Someone with more knowledge should probably chime in, but the high HC is due to unburnt fuel. Is your ignition timing set correctly? ( There is a correct way in doing it.) Plugs fouled up? Leaky injector(s)? That is all I can think of at the moment.
 

gvr4ever

Well-known member
Joined
Aug 6, 2002
Messages
6,190
Location
central Indiana
Do a boost leak test too.

When I passed in IL (I realize not as strict) I ran the tank low, put a few gallons of 89 octane in, lowered the boost and got the cat as hot as I could before the test.

BTW, I ran a 2.5" high flow cat too, not stock

Might want to make sure a previous owner didn't install a EGR plate or something.
 

transparentdsm

Well-known member
Joined
Jul 27, 2011
Messages
3,690
Location
Cherry Hill, NJ
I had this issue when I snogged my Laser a few years back in Tahoe and as stated above check base timing, my issue was from being at like 8-10* timing, i set it to 5* and passed. The guy at the smog station was blown away with how low my numbers were after the timing was corrected.
 

mk2davis

Well-known member
Joined
Mar 1, 2015
Messages
191
Location
Ventura, CA
So I had the cat replaced for 250 including labor, which where I live is a steal. The numbers are now in the single digits and I am totally street legal!

Yet, I can't shake the idea that maybe the new cat is hiding some dirty little secret. The base timing was set correctly by grounding out the connector. But that was before I sent the ECU off to be inspected. Just to be on the safe side, I'll recheck that. The plugs are new, as are the wires. The air filter is clean. The injectors were recently serviced by RC.
 

Eztoril

Well-known member
Joined
Aug 31, 2016
Messages
80
Location
Irvine CA
I might get heat for this suggestion but you can run a gallon of denatured alcohol with a 1/4 tank of gas and it will most likely pass. I've done this method in my m3 for years and passed ca smog no problem. Just make sure you fill it up with 93 after the test to dilute what's left in the tank. Fresh oil change helps too. Or obviously fix the problem whatever it might be. I also think the base timing would be a good place to start troubleshooting.
 
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