heres a tough one.

for a while now my car has been "popping" in the exhaust when i let off the gas or downshift, at first i thought it was a little hole in my exhaust so i got a new cat back. still did it. then i thought maybe it was the small hole in my cat, so i got one of those. still does it. now i've tried changing the plugs and the O2 sensor. still does it. i cant pass aircare because i fail on the idle test for hydro carbons so somehow unburned gas is getting in my exhaust. oh my plugs where pretty white so im guessing im running lean, which i hear is harder to ignite. Anyone have any guesses what else i can do? thanks.

what mods do you have? and what car are we talking about and what engine?

codes ?

try retarding u'r timing a degree or two. also swap in a new fuel filter. if u can check u'r fuel pressure do that. replace the plug wires. how long have u been trying to pass aircare (e-check)? i know in our county if u have $300 in receipts after u failed in an attempt to fix the problem, they'll pass u automaticly. check it out there and see if a similar thing applies. also another thing. get the car good and warmed up before u go in for the check. like 30 mins of constant driving. that way u'll have u'r cylinders at optimal temp and u'll be able to burn the mixture a little better. also wut octane r u using? try 87 octane, cuz the higher the octane rating the harder it is to burn.

a friend of mine said to use heet before you go.

i have heard that too.

were the hc's high at only a certain rpm? was anything else off at all? what did you get for CO, CO2, o2, NOx? some things that cause high hc's are, running rich, misfire, secondary ign. also believe it or not, running lean causes real high hc's. CO should be below .5%. a misfire will not affect co so rule that out if co level is fine.

I had same problem passing idle hc's so i spent 250 getting a waiver and it passed by under half of everything....but all i needed was a new distribitur cap and rotor mabey even new plug wires and it'll pass with flying colors....

Thanks for the reply's. I've got a sohc ZC with short ram & header. Im throwing no codes. I drove for about an hour before i went in for the test. and i can only get a conditional pass for 90 days if i spend $300 bucks or more. for the driving test i got 43.00 for the HC max=109, 0.13 for CO max=1.21 and 80.00 for NOx max=1713 <- wow because of the new cat i guess. my idle test was CO 0.59 max=1.01 and HC 282 max=124.
i've got those silicone "performance" plug wires that are about a year old so i dought it's that. and i'll have a look at the cap and roter tommorow, but im sure its fine. i think i changed it when i swaped the motor in January. i'll also get a new fuel filter as well.
Ones&Zeros what did you mean your friend uses heet?
thanks for the help.

sounds like your running lean at low rpms. that would make hc's high and co's low. If you were running rich, hc's would be much higher. Also, its definitly not a misfire problem since hc levels go down at higher rpms. So, you might want to check your fuel filter, maybe change it since its cheap anyways, and also run some injector cleaner. I can almost guarantee that you'll pass after that. only other things you may want to look into for reassurance i think is a compression test and check your timing with a light.

ok, today i changed my fuel filter and got my timing done. nothings changed. im stumped. i'll try to do a compresion test this weekend but the engine runs pretty strong so i have a feeling its fine, but i will check anyway. oh i also checked all vacume lines and everythings good there too.

Yes, Before You Go, Now I;m Not Saying This Is Gonna Work, But Dump A Few Bottles In There. Some Thing About The Alchohol(spell) Burning Clean.

so heet is probubly like Methyl Hydrate im guessing. ya i put some in before i went for the second test. still failed. i wasnt sure how much to put in so i only put in just under a liter to a half tank of gas.

maybe you are going in a high gear at low rpms it happens to my hb sumtimes

ok i finaly tested the compresion and it was 180 in all 4 cylinders. i also put in 87 octane gas and that seemed to help a little. i put back in my boch platnum + 4's(which i changed last week to some old ngk's to see if it helped) and i think its popping more again.