SSpeedracer

iTrader: (8)

Car failed 25mph emissions testing with too much hydrocarbons.

I'm going to try the following to see if I can bring it down. Any suggestions let me know.

Raise ECT (tested at 190F)
Oil/Filter change
Clean out intake
Warm up car on highway prior to test (idle last time)
Higher octane fuel

If the above doesnt work, I'll have to start swapping stock exhaust back on and possibly wrap catalytic convertors.

On a positive note, NO emissions were almost unmeasurable (indicates cold combustion temps). A/F was 14.7 +/- 0.4

Any ideas, such as timing changes, please post up.

gametech

iTrader: (1)

What did you measure your A/F with? High Hc is usually rich, lean usually causes high NOx.

SSpeedracer

iTrader: (8)

measured with wideband, car was in closed loop target of 14.7 AF at about 2300RPMS (25MPH)

Yeah, HC is rich or cam overlap (ie the TR220 114), less restrictive exhaust, oil blow by, a high flowing injector, fouled plug.

lean increases combustion temps which in turn forms more NO. One reason GM runs the LS1 at high temp is to reduce HC.

I keep the car in good shape maintenance wise, so plugs, filter etc are are on my list but not likely. I really suspect oil in the intake, low combustion temp, and cam overlap.

I think that advancing the spark improves combustion (less HC) at the risk of increasing temperature (more NO). Does this sound right? I'm going to add about 2 degrees at my test RPM 1800-2200

Brains

iTrader: (7)

Dump some denatured alcohol in the tank and retest. Add up to 10% by volume depending on how badly it failed. The alcohol adds extra oxygen to the reaction and cleans up the HC's tremendously. Heck look for some gas stations in your area that advertise alcohol in the mix already, some states have it and some don't.

SSpeedracer

iTrader: (8)

That makes some sense. Its hard to tell whats in the fuel, each station has warnings saying the fuel "may contain" MTBE, oxidizers, alcohol, etc... The mix is usually changed throughout the year. (winter = oxidizers) But you can never tell because the warning stickers stay up all year long.

The HC emissions were max allowable at 15 mph and 17% over at 25 mph. Being at the max allowable limit is still pretty high, but its enough to get the car registered.

I'm just glad I did a pre test so that there is no record of cars failure with the DMV.

P Mack

iTrader: (6)

I've heard of people having the air pump come on continuously (if you still have it).

SSpeedracer

iTrader: (8)

I was playing with the air pump idea also. Problem is that the test may see it as a small leak or inefficent system and assign a multiplication factor to the emissions data. Also, doesnt the computer go into open loop when the air pump is on since the O2's peg out?

I've got some ideas I'm going to try tomorrow. Higher AF ratio, more spark, hotter ECT. I'll post up after I get results. If it fails again, I'll check the plugs and throw the OEM cats back on. The OEM cats will increase the back pressure and reduce the fuel charge passing through the cam overlap. The intake is soaking with GM top end cleaner and I'll clean out the PCV system.

The only thing I'm confused about is spark timing. I've read conflicting info on how it effects HC emissions. In fact, higher octane has a slower flame front so it may make more since to run lower octane. Ahh the chemistry I learn in my quest for speed.

SmaknaSS

iTrader: (1)

Seems like pumping cool air into exhaust side of a hot engine would be BAD, Wouldnt the cool air from the AIR pump possibly travel up one of the pimarys and possibly warp an Exhaust valve? When the engine is cold I dont see a problem with cold air injection(as when air is normally injected to light off the cats) but with the engine hot seem's like a bad thing.