My 91 hatchback I got a few weeks ago has to pass emissions before i can register it. It's on the original d15b1 motor which I'm tossing in a month but i need it to pass for the moment. it passed everything except hyrdocarbons so I replaced the wires and plugs and I did notice oil on the old plugs so I'm guessing the pistons rings are bad but I don't want to have to replace those on a motor I'm getting rid of. I retested and it was better but still too high. Is there anything else I can do to make it pass? Like additives or something?

 

throw on a new cat, it wont reduce power output (at least anything you'll notice) and it'll decrease the HC's enough to a reasonable level.

 

CEL codes?

Cap and rotor replaced?

Set the ignition timing to spec?

 

May i ask what's your CO% numbers?