Are my Cats Shot?


Founding Member
Aug 30, 2002
I have a 1990 5.0 Hatch and recently had a MAC catback system installed. I also have MAC ceramic coated headers. However, my catted h-pipe is still FORD stock.

I had the catback system installed in early May and just 2 weeks ago I started getting a "clack clack clacking" sound coming from underneith the car around where the cat's are. This clacking sounds is most noticible on cold start-ups when accelerating and decelerating within the first 5 minutes after start-up. There is no sound when idling in neutral at a stop sign, nor when I rev the engine. After the 5 minutes of driving and when the car hits operating temps, the "clacking" sound disappears.

I've checked under the car for loose fitting pipes or parts that have fallen off the hangars and everything seems solid and unmoving.

FYI I had a Tri Ax shifter installed in April and have had no shifting issues before or after the install and it feels fine (no grinding gears, vibrations etc). My drive shaft was replaced last fall with an aluminium and there is no "clunking" while underload or acceleration. I can decipher this as my stock iron shaft was shot and clunking. Nothing seems to be rubbing ot touching other parts and I don't feel or hear any noise from the floorpans to indicate the exhaust system is loose.

My only assumptions are that either the element inside one of the cats is shot and moving/floating around inside the shell and upon the pipe heating up, the element expands and hence stops moving about, or maybe the fitment of the FORD h-pipe is not great with the MAC's and once the pipe heats up and expands, it fills up any void between the 2 pipes.

My question is 2 fold. What are signs of bad cats and what else could it be?????????????
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