I aggree with the backpressure being a myth but its much easier to say backpressure then to get into keeping the piping fairly restrictive to keep the exhaust as hot as possible to keep its natural entropy....etc etc you know that old chestnut hehe.....

 

Maddog:

Actually, I have performance gain now that the leak is fixed. I'm feeling more power behind the pedal

I just never saw what this truck was like before the problems I had so I was just wondering if there was a surefire way to tell.

 

Good one!


Guys, backpressure is not a myth but it does depend greatly on the engine setup (HP or torque motor and normally aspirated or turbo/supercharger).

 

So would a 2nd gen 4 runner gain or lose either hp or mpg by having the cat removed? or would it or would it not cause the o2 sensor to fail/cuase the check engine light to go on?

I know its an old topic but I was wondering.

 

My experience with my 2nd gen - others mileage may vary. Mine runs a teenie bit better without the cat. It got 1-2 more mpg. It revs quicker (if you can use those terms re a 3.0) and feels noticeably more powerful between about 3000 and 4500 rpm. THese weren't HUGE differences, but they were noticeable. It sounds like crap however, the cat smooths out the exhaust note. The o2 sensor is before the cat, and has been unaffected. Been this way for 80,000 miles with no side effects. ON the other hand, the cat may not have been in prime condition before it was removed either. Hard to say if it's a performance benefit really. When I get around to doing something with headers and the exhaust, (or do an an engine swap) a cat is going back on there though.

 

tap on the cat with a hammer, if it sounds hollow it was gutted. My 87 that I owned many years ago was gutted...

 

Not sure why you don't just remove the 2 bolts on one end of the cat and have a look inside. If the bolts are rusty, cut them off and replace with a couple of 3/8" s/s bolts and nuts. And if you find the cat is intact, you can also inspect the inlet end to see if it is clogged or not.

 

This is embarrassing, But ten years ago, I thought gutting the CAT on my '93 4x4 might help out. I ran it with a straight through pipe for a few years, blowing the factory and every other muffler within 10k miles, until it started failing emission tests. I had to replace the cat to pass, with a unit that was maybe a quarter of the size of the original. It was really a self inflicted wound. These Toyotas are very well tuned out of the box for all but competative performance levels.

 

If the cat s gutted the exaust will sound kinda hollow

 

My flanges are welded together :pat:
It'll make header installation fun since I don't have a sawzall and I don't know how to weld

 

my name is andy and i also drive a 91 4runner... i have this question, when i acclerate there is a very loud ticking noise as if the exhaust was leaking. how can i figure out what the problem is. My mileage is also very bad! so if anyone has any ideas please let me know thx! andy

 

Mines ticking also....I think that is from the cat gaskets?? well I can feel air coming out from where the flanges are connected.

 

I just had the same problem. Just soak the nuts and bolts with PB Blaster or Kroil and uae a breaker bar or impact gun to undo the old bolts and nuts. If you are going to reuse the old nuts make sure you crush the end that has a slot in it to make it lock again, or buy new stainless hardware so it won't rust. Put new gaskets in. Spend the money and get some from the dealer, I have had bad luck (4 sets) of the felpro gaskets not lasting.

Andy,
Look around the exhaust manifold, under the heat shield on the exhaust manifold, the down pipe where the Y is welded, the gaskets where the manifold and Y pipe connect, and at the cat converter. These are all the places my truck has had leaks. Look for discoloration on the exhaust manifold (black or white streaks/ areas) I had a hairline crack in mine under the heatshield that was a pain to find.

Hope that helps guys.