Cal Club Autocross Forums

125k miles 22 years old, origianl equipment 1990. What's the chance I am losing meaningful hp and tq to my 3 Cats?

Occassionaly through a check engine light when the car is driven for awhile. Being OBD1 chasing the code has been a guessing game. Was thinking OEM 22 year old cats might be tired or clogged.

Are you sure the code is relating to emissions? If it's not too difficult pull the mid pipe off and see if the honeycomb has melted, might be your cats have failed, usually from running rich.

Failed cats can keep your engine from running, so its possible you could be losing quite a bit of power, but if the cats are fine you could probably gain 10 hp having them removed to the extent the rules allow.

Arthur Grant wrote: Was thinking OEM 22 year old cats might be tired or clogged.

Isn't it more likely that the cats are burnt out and supply less restriction than new OE ones?

I don't remember now if you're stock or SP. Obviously not much to do in stock, but for SP, if you're not passing your next smog, I'd go with nice high flow cats. If you're still passing smog, I'd leave it alone.

Jay W

Still passing smog, just regularly get a check engine light when warm. Being OBDI I haven't had any luck isolating the fault.

Running BSP

I have been told the removing the Cats wouldn't improve HP a lot but would significantly improve throttle response?

My problem is the California Corvette had 3 Cats. Two pre-cats and a main cat at the x-pipe.

The pre-cats were added to the C4 in 1986, has nothing to do with being a California car, all US models got them. There are aftermarket Y pipes that claim to be 49 state due to having no pre-cats, but you wont find a factory built US car with only one cat after 1986.

If the pre-cats were bad you would know, when the car is running it sounds like a box of rocks is rattling around in the trans tunnel because the bricks break up. When it gets bad enough these pieces start to block the main cat, and the car wont rev. I have experience with doing the track-side repair of beating the pipes on the pavement to get enough pieces out to drive home.

There is great power to be found with a proper exhaust system on the L98. But if you are going to do it, do it right the first time, get a set of good headers and build a complete system.

I would suspect an 02 sensor or the EGR valve on the intake if you have an interment emissions related CEL.

Well I feel better about the CATS. Have replaced the O2 sensor and EGR valve. Car runs fine, the check engine light doesn't seem to mean anything I can find.

The problem with the headers is there is no one who makes Cal legal.

Depends where you live, but I just had a really hard time getting a stock c5z passed. By hard time I mean the tech spent (no exaggeration) 30 min on the visual ck. My car is low & he used a mirror/light on both sides of the car to inspect the (stock) cats. He said the PCV was missing (in 04 they moved it under the intake) because it did not match the diagram BAR / CARB provided. He called a local Chevy dealer & they faxed him a 2004 diagram which proved the change.

I don't think he was incompetant, just was inspecting to the "letter of the law" and BAR / CARB gives out bad documentation (surprise, surprise).

After all the BS he probed the exhaust & it was WAY below the limits, very clean.

Whole thing took almost an hour, don't know how that shop stays in business, as I only paid $35 with a coupon for the whole smog cert. & all.

So be very careful what you put on there.

Arthur I know of a smog shop that has been pretty lenient with my Mustang which is quite obviously modified and lack of carb stickers. He didn't seem to mind the mods so much as I wasn't trying to hide them but I think if the car passes the sniffer you'll be okay. I will say he's a bit expensive I think I paid $65 but the car passed and it wasn't much of a hassle.


FIX it...KJ ;)

Bobby Beyer wrote:Arthur that smog shop across the street probably doesn't want to be found using google.

FTFY

Arthur is my neighbor and there is only one smog shop, that I know of, in our area.

I also don't want to publicly advertise a company that may or may not be using best practices when it comes to following California emissions law.

Bobby Beyer wrote:Arthur is my neighbor and there is only one smog shop, that I know of, in our area.

I also don't want to publicly advertise a company that may or may not be using best practices when it comes to following California emissions law.

You mean like posting about it on a public forum where anyone could google your address/area and find it?

If your googlefu is better than mine let me know but my address isn't associated with my name afaik. Not wanting to get too far off topic but there are like 7 smog shops less than a mile from my place. Arthur if you want to know the name please pm me.

Never mind!

I think everyone is asleep at the wheel today....

Davin - that's what I found. Of course, I emailed it to him.....

Is anyone here actually gainfully employed? Oh...we ALL are. ;)

9/80 ;)

Bobby Beyer wrote:9/80 ;)

Judging by the time stamps, I'd say it's more like a 4/20 break.



Jay W

Jayson Woodruff wrote:

Bobby Beyer wrote:9/80 ;)

Judging by the time stamps, I'd say it's more like a 4/20 break.



Jay W

by Bobby Beyer on Fri Nov 30, 2012 3:24 pm

I think you might need to go up a few sizes on those glasses


I've been watching "My cousin Vinny"

The timestamp is an hour off on the server hosted in Germany.

Even though it's OBD I the code number would still be useful to know. What number is it?

Most codes can easily be ruled out as being related to the cats.

If you haven't checked the code, you don't need a scanner, just connect a jumper between the A and B pins on the ALDL connector, then turn the ignition on. See full instructions here: http://www.corvettebuyers.com/c4vettes/codes.htm" onclick="window.open(this.href);return false;

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Jonathan Lugod wrote:P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

I would check the fuel injectors. Do a pressure hold test to see if one of them is leaking.

Jonathan Lugod wrote:P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

That's an OBD II code.

Bobby Beyer wrote:If your googlefu is better than mine let me know but my address isn't associated with my name afaik. Not wanting to get too far off topic but there are like 7 smog shops less than a mile from my place. Arthur if you want to know the name please pm me.

I know who he is. He's a good guy. Gotten more conservative. My thing is I want the car legal, wasn't planning on pulling the cats for the street. Not sure there is that much to gain even if you do. But was wondering if they were causing my system to throw the code.

Actually I usually use AAA in Costa Mesa. They always ask what has been done to the car, but the car is bone stock under the hood, except for the after market chip, which I am not convinced does anything, but it's there. The only other mechanical change is the mufflers were removed and replaced by tips with glass packs. Thus the rumble.

Jonathan Lugod wrote:P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

?????????????????????

Jason Isley BS RX8 wrote:

Jonathan Lugod wrote:P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

I would check the fuel injectors. Do a pressure hold test to see if one of them is leaking.

Injectors are new, matched set.