Removed the Cats & now runs Terrible! Help

i hope your problem is only the fact that the air pump air lines and the emissions test lines to the manifolds must be capped off. otherwise you have burned exhaust valves on one bank. i would not drive the car until your shop can look at it. they should have never let you leave and drive the car this way if its doing this. if your car is fuel injected i would check the 02 sensor as well.

 

He doesn't have an 02 sensor on a GTSi. Are you getting popping on deceleration?

 

universal cats work just fine on the car, but make sure the installer isn't an idiot. Some of them will simply cut the old cat out...including the flanges on both sides of the connections, and weld in the generic cat.

You want a shop that will weld oem-style flanges onto the generic cats, and either transfer the thermocouple bungs, or install new ones. Then bolt the cats in.

btw, it's normal for the exhaust to exit the muffler unequally.

 

What does it mean if this is happening?

 

The difference in exhaust flow from one exhaust pipe to the other was completely normal as I and several others told you at the time. A clogged cat did not cause it. Also removing the cats will NOT cause your car to run bad.


As a result of a total misconception you have performed a variety of modifications to your car only to cause it to run badly and that misconception and a lack of understanding of the car and its systems continues to haunt you in your attempt to fix it.


I strongly suggest you bring the car to someone who can actually diagnose and fix it.

 

I have a set of hollowed-out, OEM cats on my '79, and it pops on decel (more like "burbles"), and the exhaust flow is MUCH less coming out of the right bank of pipes vs. the left...

Just my 2 cents.

 

I just put a Hyperflow on my car. It is just great.

Vs. a Test Pipe:

NO change in sound (I have a Tubi too)
NO loss of performance
NO more exhaust stink blowing into the car.

Really, skip the test pipe and buy the Hyperflow. It is really a no-brainer once you have tried both.

 

I did the same to my '83 308. Removed cats, installed straight pipes, capped off air injection system, and removed tubing. The car ran great without any other mods.

Sounds like you have more af a problem.

Oh, it did burble on decel. I think it may be due to decreased back pressure. No affect on performance.

 

I had an '80 308 2V. I was running a Borla exhaust, no cats, disconnected air pump, and also heard the burble on deceleration. My experience was no Problem, normal!
I believe you are experiencing the same thing...correct?
Only issue is the bogging down/ loss in performance after these mods.
one isssue is the decrease in back pressure (from removal of cats), but I'm not certain if the fuel mix needs to be re-set (richer?) since you don't have cats.

Anyone else have an idea on re-setting the fuel to a richer (very slight adjustment!!)?

Or should he just try a leak down & check those valves?

 

Car ran OK before, does not now. Some act of human intervention needs undoing and it is not the cats now or in the begining.

This reminds me of the old days when cars got retrofit PCV systems installed to replace the road draft tubes. People thought anything related to smog control was bad then too and just disconnected and plugged them. Right up until the oil pan gasket and rear main seals blew out.