I passed ca smog today. Just. HC at 15mph (1774 rpm) was 78 which is the max allowed. 25 mph (1719 rpm) was above average but well below the max. The test guy suggested incomplete combustion and maybe the cat needs replacing. I'd rather the engine burnt the fuel than the cat so is there anything in particular I can check on or fix? Engine has 124k miles, thermostat is 160 degrees and injectors were replaced a year ago. CO is above average but ok and NO is way below average. I've got 2 years before I need to worry about the smog again but I'd really like to get the most I can from the engine and use all the gas I'm paying (through the nose) for. Any help appreciated.

 

Anyone?

 

You are running that engine too cold, it needs to be 170+ to run half decent. I would also check the spark plugs, can tell alot from the spark plugs, chances are it might be running rich, but I would bet that your main issue is running too cold.

 

I've read several 160 v 180 discussions and have been planning on trying the 180. It used to run very rich but I found it was the injectors so I replaced then and it's been much better. The plugs looked not bad when I pulled them a while ago. Not sooty like they used to be. Thanks for the help.

 

I would just go with the stock 195* F thermostat. Even with a 180* the engine doesn't run as well as it does with the 195*.

RBob.

 

Do a fuel pressure & leak down test on your injectors.
Make sure the vacuum hoses are in good shape, esp the one going to the map sensor.
Test the coolant temp sensor.
Check ign. timing & make sure it advances when you rev it.
Check the ecm grounds.

 

I would have to see your full smog report but I can tell you if your old injectors were leaking causing your rich condition then it might have damaged your cat, but there are a bunch of things you need to check before you replace a cat converter (A converter is the last thing replaced on any vehicle being diagnosed for emissions) also running a thermostat that cold will keep the car in open loop and that could also be the cause of the high hc. You want to drive your car around awhile before you take it to get smogged, you want to get it smogged warmed up and not cold.The test guy shouldnt have said anything or suggested any parts be replaced without being diagnosed first. I'm a smog tech in california, I smog them and diagnose the failures and the 3.1 usually doesnt have a problem.