pityocamptes

1998 Honda Civic EX. I know a fully clogged cat will absolutely kill any power, etc. Since its been 15 years on my honda and 92K miles later, I have never replaced the cat. If the cat was crapping out, but not fully pluuged or defective, would you get a CEL, or what would be some other warning signs? Thanks.

X E Ryder

You might be surprised how much happier your car is with a new, maybe also free-flowing, cat. That's pretty old!

Former User

A bad cat should throw P01420.

A clogged cat would cause a loss of power in the engine.

Telecatster

Being that your car is an EX model it has a bolt-on cat. You could remove the cat temporarily to see if it runs better. It will throw a CEL but it's related to the post-cat sensor (#2) and can be ignored, and will not effect performance.

pityocamptes

Might give it a try I have noticed lately that gas mpg is sucking...

Telecatster

http://www.ehow.com/how-does_4899113...onverter_.html

Bad mpg's could be related to a number of things but if it's running fine the most likely source is a weak o2 sensor. If an o2 sensor has not completely failed, yet is weak it may not throw a CEL code. If you have not replaced it for the life of the car and it's approaching 100K miles it is a likely suspect. If you decide to replace make sure you get Denso OEM. Hopefully others will chime in as I don't wish to mislead you.

crazyhouse2011

Oxygen sensors are a ***** to replace. Good luck with that one mate.

X E Ryder

Kroil or other rust eating spray and soaking is good here. Use a socket, do NOT round off the flats with a crescent wrench! An impact is the best - drive up to a garage and offer to buy the tech a couple beers for busting it with an impact ($10 bill) and you will never regret the savings in time and headache!

crazyhouse2011

wouldnt that destroy an original cast iron header with a small amount of oxidation on the surface?

X E Ryder

Only if the guy goes Texas on it with the gun - a good snap-on socket with patience and half trigger, warming it up can remove some pretty stubborn O2's - Geez I've been there!

Good point though - Handle with care!

Telecatster

Again, the o2 sensor is my guess and from my own experience. It can be tested for voltage output, but that doesn't always indicate failure or weakness.

For an o2 sensor removal get a crow's feet socket set at autozone under their free tool loan program. It's a set of sockets that has varying heights and sizes that have a slit on the side to allow the socket to slip over the o2 sensor wire.

As X E Ryder stated soak the o2 sensor threads with Kroil, PB blaster or similar lube and let it sit for an hour. After an hour warm the engine from cold start until the temp gauge rises to the first white line only, shut off the engine and then proceed to remove sensor. Go slow and use consistent force while loosening. Do not use a hammer or other tool to tap to initially loosen as it may strip the threads. Even with slow consistent force if the o2 sensor has been in for a long time or been subjected to excessive manifold heat the threads may well strip anyway when removed. Best to have the new part in hand when removing an o2 sensor due to possible thread stripping. When putting on a new o2 sensor there is o2 sensor grease that can be used to help avoid stripping during the next replacement. The grease may be included in the package with the o2 sensor so checkk it at time of purchase. Also, don't over tighten a new o2 sensor and follow torque specs as obviously the manifold heat will expand the threads.

black97civic

Try and rent a back pressure gauge and check Back pressure while you have the 02 sensor out. It's the best way to check for resistance in the cat. I've seen clogged cat not set of engine lights on obd2 cars btw.