HT4100 4.1, 4.5, 4.9 Discussion, Removing cat-converter...good idea or no? in Cadillac Engine Technical Discussion; Just wondering what would happen if I remove the cat converter and replace it with a pipe of its length ...
Only OBD2 cars will know the difference. Some EGR valves are calibrated with a certain amount of backpressure (aka , the positive and negative backpressure EGR valve types) and will open at the wrong time causing some potential drivability issues.
Most are positive types. Meaning it takes a certain amount of pressure to even allow the valve to start to open, lose the pressure and EGR doesn't function often at all, so pinging might start to occur. So then you have to run higher octane or reducing timing, often at the expense of what you were trying to gain.
So, if it works, leave it alone, if not, then take the chance, if it fails to work well, then put one back in....
You might try disconnecting and plugging the vacuum hose that goes to the EGR to find out whether or not it pings.
I've got my EGR disconnected and it doesn't ping even with 3 degrees advance and the cheap 87 octane gas.
Instead of removing the cat. How about rodding it out. You can lower the cat by unbolting it from the collecters. Take a large hammer/rod and break up the honey comb innerds. Once finished, connect the hollow cat back up. Start the engine up and rev it several times and watch all the junk fly out the end of the exhaust pipe. You might want to disconnect the muffler before doing this since your wouldn't want all the junk to end up in there.