I got the Z smogged this morning, and emmissions were over on everything at the 15 and 25mph test. I was thinking its a bad catalytic converter (180K on car and its the original cat) but I'm not sure. Last time it was smogged the readings were around 1/10 of the maximum, absolutely perfect. But my cars been getting ****ty gas milage lately as well. Any suggestions? I have lik e $400 to my name, and I was planning on getting headers, but i'll put it towards fixing the car if I have to. Thanks.

 

Why not get one of those fuel injection cleaning bottles, with full tank, run it till tank is empty, then fill it up and take it to the smog place. There are some specially made for smoging purposes. Give that a try its only 6-8 bucks. If dont work , then maybe your cats are bad. Maybe thats the reason why youve been getting ****ty milage, could be one of them is clogged or something.

 

What about your 02 sensors? if those are bad i bet they could screw up your emmisions and cause bad gas mileage. just a thought.
Dan

 

Well that was my first thought. Smacking the cat w/ something I don't hear any weird noises (if a cat was coming apart you'd hear stuff shakin around in it). Would a bad 02 give me a SES light? Should I just go get it scanned and see if I get any codes? I just don't want to spend money and still not pass smog, as I don't have very much of it.

 

I dont know how it possibly did, find out exactly why it failed, and it shouldnt be expensive to fix..GM can do that for ya

 

If you are starting to get bad Gas milage it is a indicator that your O2 are going bad. Plus with that many miles on your CAT its probably on its way out. You can get a CATCO cat from Summit or jegs for about $90 bucks then if you get to a local muffle shop and ask how much they can install it for. I would say with $400 bucks total it can be done. Good Luck.

 

I say change your O2 sensors, its surprise how much of a DRAMATIC change as far as fuel efficiency goes, not sure about emmissions although I know O2 sensors do have a pretty decent impact on them aswell... Normally but not ALWAYS, when an O2 Sensor is going out, you'll get an SES light... (we've rode around with the "idiot light" on for about 6 months before we finally replaced the O2 sensors on my dad's Z...) Eventually if you don't change your O2 sensors, your car will become more sluggish, have a hard time starting and get to the point where it will simply quit on you.

I say change those sensors and throw some fuel injector cleaner in there with a full tank...Even if it doesn't work at the very least you'll have new sensors in the car to prevent further problems, and you'll have a clean tank !

You may also need a tune up... (sparkplugs, oilchange, ect ect...)

Just don't overlook the basics because it always seems to stab people like me in the back.

If all else fails then yes it's more than likely your cat...

hope this helps man...
good luck.

 

My sons 94 Z just failed to (Bone stock) I checked the gap on his spark plugs and it was .075 Twice what it should be. I'm going to put in new plugs and maybe a Cat and it should pass. I would do the simple stuff first like checking air filter, Plugs, O2's and Cat. I just bought a high flow stainless cat on ebay for $65 shipped for my other Z, They have a ton of them on Ebay.

 

I put a bottle of fuel injector cleaner in there every few tanks. I change my oil every 2K miles w/ semi synthetic, it's got about 500 miles on the last oil change. I did plugs and wires earlier this year so I don't think that's the problem. One thing I noticed, some times when I start my car it will stumble and just die if it don't give it gas for a second, but then it runs fine afterwards. the haynes manual said that was a symptom of a bad egr or a vacuum leak, so i'm going to look into that as well. I really don't want to have to replace the cat because its gonna be the most expensive thing to do, but if that's what it takes i'll do it. how much do 02 sensors run for at kragen or autozone? Is it something I can realistically do in a few hours? (i'm pretyt mechanically inclined, i've never let a mechanic do anything to my car). Thanks for the help people. I just want to get it fixed so I can get my new tags and not get a ticket

 

Before buying new 02s' take off the EGR valve and see if it has carbon build up on it. Get a wire brush / carb cleaner and clean it up. If you need new 02s' it cost about $60 each also stay away from aftermarket ones and stay with AC Delco brand.

Vinny

 

thanks for the advice. tommorow is my day off so i'm going to try some stuff