Smog help: need to reduce HC

Yet another question for the experts... :)

I almost passed the smog check, but failed the HC @ 25mph (I had 50ppm vs. 37 max allowed).

I did all the usual tricks (got it really hot, etc), and it came pretty close.

So my questions:

1) What impact does ignition timing have on HC? If I back out 6 degrees across the board, will that help or hurt?

2) Both the 15mph and 25mph test were done at 1700rpm (due to my torque converter). I could theoretially rig the shifting tables so that the the 25mph test was at 2500rpm. Since I have a cam, would that help? Would having the torque converter lock up during the test help?


Thanks,
Terry

Timing affects HC big time. Try dropping your timing.

Will do! Is 6 degrees reasonable? 8 degrees?

How much are you running currently?
Factory is about 17 deg. With a 230 cam like you have I'm guessing that you need about 25-30 deg to make it idle "nice" but probably stock to 20 deg to make it pass.

EC

Terry....

Just courious...What state do you live in? Also, is this an engine conversion? Most states do not "roll" OBD II cars and light duity trucks.

Dave

CA rolls everything. :)

I've seen road side emmissions testing in CA...sucks..get pulled over for speeding..and they pull out a portable sniffer and check the pcm for codes...

Terrry,

What's the latest? Did you get it through?

EC

Quote:

---

Originally Posted by EC_Tune

Terrry,

What's the latest? Did you get it through?

EC

---

Not yet, but I backed the timing down 4 degrees across the board, and I'm going to run a 90% gas 10% alky mix next week.

Did they measure oxygen content in your last check? If so what was it?

EC

It was .2% both tests, CO2 was 14.7% both tests. Although they measure these figures, there isn't a max for them, only HC PPM, CO%, and NO PPM.

I'm just thinking of other tricks, is there a way to rig the air pump in the PCM to stay on for the entire test?

You may want to look at the o2 crossings vs airflow in the closed loop parameters. Reduce the Mode 0 & 4 values about 150 mv and the car will run a bit leaner at idle and increase the 02 content in the exhaust. Did they have the "average vehicle" results for O2 concentration?

EC

I assume it would also run leaner at 15mph & 25mph? They don't do an idle test, just those roller tests.

Yep, you're right.:doh:

Just need to see what the MAF is reading at the test params, then adjust the o2 crossings.

Now I need to wait for the emmissions readiness tests to complete... I wish I could just force a test from HPTuners...

Result: Passed! Thanks guys

Congrats!