Should I get a new cat or not

[oleblue]

Well I removed the section of the exhaust with the cat in it to do some work on a loose heat shield under my truck. Felt kind of light, so I got to poking around and the evidently the person that had the truck before me gutted the cat. I get around 16mpg with 33's and 4.56's. Could the hollow cat be affecting my gas milage any since the 02 sensor is behind it?

 

[Wicked_Sludge]

not likely...but it would be the cause of a CEL if you have one, and if not, something was done to trick the computer.

 

[Hahnsb2]

A hollow one didn't affect my gas millage on my b2 any... But you should have a check engine light on or something because you have the after cat sensor...

 

[oleblue]

Sometimes I get a check engine light, pull the code and its either bank 1 or bank 2 rich. I just clear the code and keep running it. As long as it's not messing with my gas milage as high as gas is, I'll probably just leave the cat like it is.

 

[Wicked_Sludge]

Sometimes I get a check engine light, pull the code and its either bank 1 or bank 2 rich.

theres your gas mileage issue. dont just clear the codes and keep driving...you have an intermittant driveability concern that needs addressing.

the previous owner probably installed an O2 simulator to keep a defective catylist code from popping up.

 

[oleblue]

So what should I do, get a new cat? I always thought it was the Bama chips programmer making the CEL come on. Never seemed to come on until I started using the programmer.

 

[Wicked_Sludge]

it may be the programmer causing the CEL and rich codes...but that doesnt mean its not causing you to get poor mileage.

as for the cat., its up to you. if you have the money you can throw a cheap universal on there (i probably would, just because they are pretty cheap these days).

 

[oleblue]

I may try running it without the programmer for a while and see what that does? Where could I get a cheap universal cat at? I would have to cut the old one out and weld a new one in right?

 

[Wicked_Sludge]

jc whitney sells universal cats for about $80. you could also price one out at a local muffler shop...which will be nice since you'll probably want to have them weld the new cat. on for you anyway.

 

[Original_Ranger84]

I would think that if the cat was gutted it would make it run lean because the o2 would read excessively rich and lean the mixture. also the check engine light for faulty emmisions equipment. If you have a performance programmer that would be the problem because it would advance the timing and richen the fuel mixture.

 

[Wicked_Sludge]

the post-cat O2 sensor is only there to monitor the cats. performance. the computer uses the 2 sensors on the downpipes to sense each banks mixture.

but i also think the programmer is, at least partially, the cause of the mileage and rich codes.

 

[Hahnsb2]

Muffler shops will rip you off if you buy a cat. Local shop wanted $150 for a universal, went down to an auto parts store and bought one for $50 and it worked very well.

 

[V8RangerBoy]

the post-cat O2 sensor is only there to monitor the cats. performance. the computer uses the 2 sensors on the downpipes to sense each banks mixture.

but i also think the programmer is, at least partially, the cause of the mileage and rich codes.

Correct - the cat shouldn't change rich/lean conditions at all. A system with a cat typically runs dual O2 sensors per cat. A 5.0 Explorer for example, has 4 O2's and 2 cats - the front 2 O2's near the manifolds are what monitors the air fuel ratio. The back 2 compare readings with the front 2, and from the difference in readings a "performance check" on the cat is determined. Thus, when you take the cats out, the sensors are reading the same value, and a CEL is thrown on for the cat not doing its job.

If the previous owner used a simulator, it still shouldn't affect the rich/lean condition unless the simulator was (for some reason) connected to the front cats as well. Typically the simulator only works for the one sensor, so I don't imagine this is the case. The programmer could be the problem, or you may have something else lurking around....

Run it without the programmer for a while, and on stock tune if you can, and see if the light stays out. If not, get'r checked out.

 

[oleblue]

I'm gonna put the stock airbox and filter back on it, clean my MAF sensor and throttle body of the K&N gunk and run it on stock mode and see what happens. From what I've read most people get better milage out of the Bama chips tuner, something else may be messed up like was said, but I'm gonna try that and see what happens and probably just leave the cat like it is.