Can anybody tell me factually if removing the cat will decrease ex. Back pressure causing the ECM to go to full rich mode. Thanks Chris

What vehicle? FI or carb?

If the cat is blocked it would. Could be a bad O2 sensor.

Use a pressure gauge in front of the cat and see if the reading is higher than 5-6 psi. You could do that right off the O2 sensor bung.

Yes, in most cases the removal of the cat decreases the backpressure more than enough to cause the EGR system to think there is a failure and the ECU goes into limp mode.

The EGR will work regardless of the back pressure of exhaust system since they are tapped into the exhaust manifold or the head. It functions via vacuum or a solenoid via the ECM. Some measure flow, some don't.

A plugged EGR passage can get plugged and it may not set a code but can make you fail smog.

Yes it may run better with no CAT and no EGR but finding the real problem is important.

What vehicle??

If doing a custom 1.75 exhaust with calmini headers and a magnaflow trichamber exhaust... Provided you bunged the 02 sensor on an efi 1.6...in my mind it should work perfect... Right?

Sniff test doesn't matter to me, mpg does. On short trips your cat doesn't do anything but kill mpg/power.

Sorry it is a 93 sidekick ca. Vehicle. I removed the cat because everything inside was in a million pieces rattling like crazy.But ever since it is getting only about 20 mpg instead of around 26 mpg.I've tried diff. Ignition timing,the jetway for the timing belt is good.

Just removing the Cat can make the car run wrong, hence the bad mileage. The motor is tuned for the back pressure AND correct reading of the 02 sensor.

Have you pulled any codes yet?? You could just throw a cheap cat on it.

If you remove the Cat in a Ca vehicle there is a $5000 for each item removed if caught, and they do roadside checks sometimes. Beware.

In Yuba DOT is stopping Diesel Pickups and looking for the car and other items removed. They tow and tag the vehicle not allowing it to be driven until repairs are made.

The state only wants something of value,not something that is going to cost them to get rid of.I think I'm pretty safe on that part. Thanks for the info.

I am SOOOOO.... Glad I DON"T LIVE IN CALIFORNIA !!!!!!

I am starting to believe the Old Joke.....
"The World is NOT LEVEL !!!! It's on a Slant, and ALL the Fruits & Nuts rolled to California!!"
Not that we don't have our share of Crazies in Wisconsin....Gov. Scott Walker/Dallmer/Ed Gean.. All fed/feed on humans !!
Yes I am for clean air/water/land......
   But we all can't BUILD a plastic bubble to protect us ALL from the practical world.
We have Nuke Power, Battery Cars......But NOWHERE to get rid of the Radioactive Waste & Spent Batteries !!!
Carbon Based Particulates are heavier than air, & will settle out of the atmosphere, it is just that the west coast
of California has a Mountain Range to the East that "Concentrates" the Air there.
Neither leave good choices.

My 2 bits......CAPT

The Suzuki engines do not run well without the cat or EGR system functioning when running the stock ECU, for it too function correctly an entirely new engine management system will be required, but dont expect to pass any emissions test, LOL

I swapped over to a heavy metal spun cat on my Sidekick, in NY if the vehicle has 80K miles or is older than 8 years the stock exhaust system does not have to be installed, but a functioning cat and exhaust is required and must pass a sniffer/dyno test as well as have a functioning OBDI or OBDII system(unless the car didnt have any(real old)).

We only need a smog check every two years and there are several counties where they are not required unless transferring ownership.

Sorry it is a 93 sidekick ca. Vehicle. I removed the cat because everything inside was in a million pieces rattling like crazy.But ever since it is getting only about 20 mpg instead of around 26 mpg.I've tried diff. Ignition timing,the jetway for the timing belt is good.

Is the Check Engine Light on?

Quote from: Wilnailu on December 19, 2011, 10:54:36 PM

Sorry it is a 93 sidekick ca. Vehicle. I removed the cat because everything inside was in a million pieces rattling like crazy.But ever since it is getting only about 20 mpg instead of around 26 mpg.I've tried diff. Ignition timing,the jetway for the timing belt is good.

Is the Check Engine Light on?

no the CEL is not on