failed smog hydrocarbons, any advice?

[tonexj]

i wasnt off by much, and only at the 25 mph mark. what affects hydrocarbons? the jeep had a blown head gasket before i bought it and i put a new head in, maybe coolant hit the cat when it blew before? i dunno! help please

 

[oldradiostuff]

Probably oxygen sensor, it controls air/fuel mixture and if it's running rich it is likely that. You did put in new plugs and change oil/filter before getting the smog test done, right?

 

[tonexj]

yes

 

[squidd]

Bad CAT would do it too. Blown head gasget might have sent a bunch of coolant through the exhaust and killed it.

 

[killer98xjsport]

i wasnt off by much, and only at the 25 mph mark. what affects hydrocarbons? the jeep had a blown head gasket before i bought it and i put a new head in, maybe coolant hit the cat when it blew before? i dunno! help please

Hydrocarbons are unburned fuel vapors and can be cause yes by and oxygen sensor and cat. But for the cat and o2 to work properly you need to make sure your ignition system is in working order, spark plugs wires cap and rotor. If these things are worn the hydrocarbons will be up. An oxygen sensor can only change the fuel mixture so much and can not keep up if your vehicle is not up to par. Check the easy stuff first. Also check you air filter plugged filter will cause a rich condition and agian cause hydrocarbons to go up.