The HP and TQ numbers in the sig were done with a tune on a dyno and a wide band O2. Shortly after that, I had emissions . . . that I promptly failed. Turns out the Carsound Cat was clogged or broke, or whatever it is when the cat fails to do its job. So I purchase a Magnaflow Cat (stepping up I thought) for it. I pass emissions, but my mileage seems to have dropped 1.5-2 mpg and the power doesn't seem to be there (atleast from my butt dyno).

Is it possible that I leaned out the mixture too much by putting a fresh cat on it? Before, as with most TBI's, we had it a tad on the rich side all the way through, but according to my Stewart Warner A/F ratio gauge (yeah, I know they're not the most accurate thing in the world) I'm hanging out in the stoich area alot.

I didn't think a new cat would effect it that much. Ideas? Comments? Suggestions?

Thanks boys.

 

Better get it checked right away....sounds over rich and will cook the cat in no time.

Most likely why the other one was bad

 

The other one cost $40 and was 5 years old and lived through numerous chip tunes.

 

You asked if you were running lean? How would this make your mileage go to crap? This is definately an oxy sensor issue.... you have recieved no light?

 

I am willing to bet that your O2 sensor got FRIED when the cat was welded into place. I have seen it more times than you would imagine. If the welder gets grounded to say the chassis and you strike up an arc with the pipe, hundreds of amps go towards the path of least resistance. That may just be the ECM and O2 sensor. The end result is the 02 sensor is damaged.

 

Well the gauge does go up and down and does respond to me putting foot into it . . . so I think it's ok.

 

Just Gut it, do you really need a cat?

 

Obviously...

As he said in the first post he couldnt pass emissions, thats why he changed it in the first place!

 

But what I meant to ask was is he dead set on passing emissions or can he just really not get around it?

 

Yes, I must pass every year until it's 25 years old.

And by stoich, actually at idle it hovers on the lean side of stoich, being especially on the border at idle when cold. I think I'm going to bump up the fuel pressure 1 psi at idle and see if that helps . . . I would rather buy a new cat than a new motor.

I'm just really suprised that going from a sh*tty clogged cat, to a really good new cat would cause this much of a change in the tune.

 

where would the electricy go?

up the wire of the O2 into the ECU then out the through the ground on the ECU?

 

It could be a fault O2 sensor but I doubt due to welding. Those sensors take a beating from heat everytime you turn the key. I am sure you will get this worked out dude. One other idea I have, not saying its a great one... disconnect your battery for 10 minutes and then connect it. Let your ecm relearn everything, that way it can adjust for your new modification.

 

Its not the heat, it is the amperage that can flow through them.

Yes, it goes through the ECM.

Sounds like it is working OK though as he has his A/F ratio gauge still working.

 

wouldn't that fry the ECU as well though

 

I am still betting that when he disconnects the battery for 10 mins he will be golden... when i built imports, there was this guys honda, every time you do a mod you have to reset the ECU. His computer would not recognize the modification unless you reset the ECU, then when he would everything would sync up. i am not saying thats the case, but whats 10 minutes of your time?

 

Won't disconnecting the battery also clear out all of the old SES codes as well?

I did turn up the fuel pressure by 1 psi and it seems to run alot smoother.