HC Emissions too High

[TexasPettey]

I took the car in today for inspection, and I failed the HC emissions tailpipe test. Not being an expert in this area, I did some research. From what I've found, high HC can be caused by incomplete burn, rich mixture, or bad cats.

I'm thinking I'll do plugs and wires, although my wires are only 2 years old and my plugs 1 year. I can use the VEC3 to lean it out a bit on the low end. I've got a ROE exhaust with high flow cats that are 2 years old. Any thoughts regarding replacing the cats?

Any other ideas around HC? Could the O2 sensors be getting old?

 

[jasontiff]

You could always "live in Wimberly" at "your sister's" or "pay a dude" extra "money" to "pass". I don't condone this but hear of it being done

 

[TexasPettey]

You could always "live in Wimberly" at "your sister's" or "pay a dude" extra "money" to "pass". I don't condone this but hear of it being done

True, but there's something more rewarding about 525RWHP that passes tailpipe emissions. Although we're modded, with the 708 CAM, passing emissions should be very reasonable.

 

[bluesrt]

i think the high flow cats are defineitly not helping

 

[Greg Good Cylinder Heads]

True, but there's something more rewarding about 525RWHP that passes tailpipe emissions. Although we're modded, with the 708 CAM, passing emissions should be very reasonable.

How bad did the HC fail the test? Work on the tune with the VEC until it sniffs good, then take it back. In addition to leaning it out a little, try adding a few more degrees of timing down low. It will burn more fuel in the chamber rather than in the exhaust. Adding timing will lower exhaust temps too, so have the cats good and hot before you begin the test.

Although the 708 is a factory cam the seat duration is pretty healthy, and it is also ground on a tighter lobe separation. Those two things add up to to more overlap and higher HC.

Something you may have already heard of....... guys will pull one injector wire off on each bank, essentially turning those cylinders into air pumps that introduce fresh oxygen into the exhaust to help burn the fuel more completely. Don't do that with a VEC. You might fry the VEC.

Good luck.

 

[Tom F&L GoR]

How bad did the HC fail the test? Work on the tune with the VEC until it sniffs good, then take it back. In addition to leaning it out a little, try adding a few more degrees of timing down low. It will burn more fuel in the chamber rather than in the exhaust. Adding timing will lower exhaust temps too, so have the cats good and hot before you begin the test.

Although the 708 is a factory cam the seat duration is pretty healthy, and it is also ground on a tighter lobe separation. Those two things add up to to more overlap and higher HC.

Something you may have already heard of....... guys will pull one injector wire off on each bank, essentially turning those cylinders into air pumps that introduce fresh oxygen into the exhaust to help burn the fuel more completely. Don't do that with a VEC. You might fry the VEC.

Good luck.

Good and hot is a good suggestion from Mr. Good. When catalysts degrade the efficiency is not really worse, they just have to be hotter to work. If the normal exhaust temperatures can't get the cats up to light off temperatures, they extinguish, re-light, etc.

Geez, I am a ****** at this. The big oil company equipment would have picked up the "pull the injector wire" trick, but I suppose the gas station equipment wouldn't know any better. I'll have to remember that one.

 

[TexasPettey]

Thanks. It was around 700 for the HC PPM vs 250 or so required. I'll work on getting it leaner down low and adding some timing. I never really even bothered to check on the O2 readings at idle or low RPM part throttle. The cats were probably not hot either, since it's just down the road from the house.

This place is nice, in that they'll sniff the car without charging me. I think they like having the car in there, especially on a Monday AM when it's empty.

 

[Camfab]

FYI , besides the tune which is very important, the stock cats are the ticket. My cam duration is larger than yours and with 585 rwhp I passed like a brand new car.
HC at 15mph......3 ppm
HC at 25mph......0 ppm

 

[viperdude118]

Thanks. It was around 700 for the HC PPM vs 250 or so required. I'll work on getting it leaner down low and adding some timing. I never really even bothered to check on the O2 readings at idle or low RPM part throttle. The cats were probably not hot either, since it's just down the road from the house.

This place is nice, in that they'll sniff the car without charging me. I think they like having the car in there, especially on a Monday AM when it's empty.

Take the car out and run it hard for 30 minutes before getting it tested..."just down the road" isn't giving anything enough time for anything to warm up.