i get horrible mpg's and i have new ngk v powers installed. my cel is on but its because im running a header and have not done the plug non fouler trick yet
I'm pretty sure if you are running without the pre-cat, your mileage will suffer. I remember Tweety said that his exhaust smells like rotten eggs at times and there is black carbon deposits in the tailpipe,... and he's got the non-foulers installed. If you've got your cell on (and it's the code you get from deleting your pre-cat) then the car doesn't go into closed loop and it runs extremely rich because it follows a predetermined MAP from the ECU.
I'm pretty sure that the non-fouler trick really only fools the ECU enough to make it go closed loop and not set off the cell,... but it must be still running very rich to leave a smell and carbon in the tailpipe. I'm thinking that can be bad in a lot of different ways. I would think that your car would run dirty all the time, leading perhaps to a clogged cat, fouled plugs, carboned up EGR, fouled O2 sensors, bad gas mileage and even rough running and misfiring.
I actually just bought the non-foulers and I'm going to install them shortly even though I have a healthy functioning pre-cat (make sure you only drill out one of the non-foulers,... there is a how-to for it). I want to use my Ultra-Gauge to see what kind of difference I see in gas mileage, O2 readings, fuel trim readings and to see if my exhaust starts to stink and get dirty.
I'm really thinking that there can be a lot of drawbacks to ditching the pre-cat that all boil down to expense and extra maintenance.
I don't think that is correct. If the primary 02 sensor is working then the car should run the same whether or not the pre-cat or second 02 sensor is bad. I'll have to take a look @ my wife's car to verify but I don't know why Mazda would force your car into open loop if the primary 02 sensor is still good.
MAF wont cause a specific cylinder missfire. and secondary 02 does nothing in terms of the running condition of the engine, it just monitors the cats efficiency. I guess other then that i would say possibly check the mechanical side of things?
situations like this suck, but you really need to hold yourself back from throwing parts at it. Although some typical maitence items that are cheap are good to start with, sometimes its best to take a step back and eliminate possibilities 1 by 1.