I have a 1990 4x4 when i had my exhaust done a year ago the muffler shop cut of the last cat off and said I didn't need it (one of my buddies).But he said I need the first cat but the o2 sensor is before the cat. I'm going to put a flowmaster 40 series on soon and the same time I was going to gut or completly remove the first cat if possible but, I don't want to if it will make my truck run bad or cause any lights to show up on the dash. Please post soon want to put the flowmaster on pretty bad.

 

On a 1990, there should be no O2 sensor after any cat, so there is no way for the computer to know if it is missing. I say get rid of it if you want to.:-)

 

I gutted the Cats on my 88 EFI. I sawed them off and then bought a large exhaust coupler (seems like it was 4.25") that I welded on the end that allowed it to slip over the exhaust pipe in front of it. The I Ubolted it back together. The pipe changes diameter very radically at the point where it phases from 2 pipes into one and then starts narrowing down just before reaching the muffler. I was unable to find ANY muffler shop that would fabricate a catalytic bypass pipe for me and actually was forced to keep my old catalytic converters and weld on the couplers to reconenct them. The shops said they'd be fined $10K if caught (its illegal for a shop to do this.) It worked out good (I like it)and the converters are constructed of really heavy metal and take welding well (much thicker walls than a muffler). I hammered out the inside of the CATS with a rebar.

 

[updated:LAST EDITED ON 03-Jan-03 AT 11:59 AM (EST)] I made a bolt in cat bypass but I took the old cat whacked off the cat itself fitted the pipe up to the pieces, got it all set, up marked it and took it to a welder and had him do it since he didn't know what it was, or care what it was, it wasn't a problem. worked great. But regular muffler and auto repair shops are supposed to know what they are doing and will get fined, so most of the legitimate ones won't do it. Here in Arizona they look for the cat at the emissions station so the bypass won't work unless you swap it out every time. Oh I did scrounge up a piece of stainless pipe for the bypass but I,m not sure you have to but when you weld stainless and plain steel in high temp applications they sometimes deteriorate faster.

 

 

Don't remove the first cat it will sound "loose". Keep it makes a better sound rumble when on...

 

High flow 3-way super Cats are available and you only need one.

 

I say keep it and here is why.

Your vehicle will have more torque.
Your vehicle will most likely get better economy
Removing the cat will create a hollow raspy sound like a cheap 4 cylinder rice burner
removing a catalytic converter from a vehicle that was originally equiped with one is illegal in the US