342kcivic

My 93 Civic has been driving just fine. I looked at the spark plugs thinking of changing them before my smog test. They looked just like new ones.

However, it failed the test. The results are attached. Prior years, it was around average. This time, it failed the CA 15 mph test for HC, CO and NO. It passed the 25 mph test for all of them.

Silly me, I drove the car about 1/2 mile from work to the shop, on a nearly empty tank. It is about time for an oil change.

I filled the tank and put in some Guaranteed to Pass CRC stuff that is well-reviewed. Should I just change the oil, drive it hard and try again? Should I even bother going to a test and repair shop first?

strategy400

Prolly time for a new cat. My '95 barely passed last tme. Guy said catalyst is prolly getting weak.

Ryan96GSR

Is that additive still in your tank?

If so I would run it through a full tank prior to the test. new oil would help. Take it for a drive on the highway to heat up the cat, and if possible keep the car running when you bring it in for the test. That should help your readings.

HondaPartsHero

What maintenance have you done to it recently? Have any mods?

B20DelSol

IF you have gone through everything:

Fuel Filter
Air Filter
Plugs and Wires
Cap and Rotor
Ignition Timing
Cam timing (probably not an issues here)
and you sensors are all working properly

I am going to lean towards recommending a new Cat. You barely passed the 25 mph test so something is happening at two different ranges that should not be. Probably the cat losing capacity

342kcivic

Recent maintenance is changing most fluids, but not oil. Looked at the plugs and they were squeeky clean.

No mods.

342kcivic

Fuel filter probably 5 years ago. Air filter 1 year ago. Wires, cap and rotor, maybe 5 years.

Never directly did anything to cam timing. Had the timing belt replaced 8 years ago, along with water pump and oil pump.

I'm not hearing any endorsements for going to the "test and repair" station.

B20DelSol

just replace those parts and go from there.

it can be a pointless to try diagnosing this problem without having a good starting point to rule out possible issues. This said, I still stand by my previous assumption (and that of others) that it is the cat.

Here is the break down:
NGK Plugs - $10/set
NGK Wire - $60 lets say
Beck/Arnley Dist. Cap - $15 (high)
Beck/Arnley Dist. Rotor - $7 (high again)
Wix Fuel Filter - $20
Air Filter - $10
All of this is $122 + CA Tax...so around $145ish out the door

Universal Cat $175

Direct Fit Aftermarket (Magnaflow, Walker)- $250

OEM - Some extreme amount...ehhh...$400 lets say.

Your choice on which route to go. I would replace the little things first and replace the cat last if truly needed.

B20DelSol

Don't forget the $5 PCV valve too!