i have a 2002 3.8 ss and im burning a lot of gas!!! i am getting the p420 code but i was told the cat was fine its just too much air flow and the car runs fine no loss of power or anything.. i filled up and only drove 100 miles and used a half tank.. ima change the fuel filter and see if that helps any other help would be appreciated

 

does the heads up display say that you are using that much gas?

 

First off, try quantifying that- are you saying that it smells like its running rich, or are you observing poor fuel economy numbers?

If its the latter, exactly what fuel mileage are you actually getting?

Whoever told you that- don't ever go back to them again, ever. The 0420 code has nothing to air flow, the cat sensors don't measure airflow- that's the MAF sensor's job up at the top of the engine. There really can't be that much that can be wrong- either the cat is bad, the rear O2 is bad, or the rear O2 wiring is damaged. I'd take it to a mechanic that knows what they're doing and actually understands how engines work.

That tells us nothing at all- the fuel gauge isn't perfectly accurate, and doesn't even have any numbers. You need to fill the tank to the top- reset your trip odo, and then next time you go fill up again divide the number of miles on your trip odo by the number of gallons- then post that number.

A plugged fuel filter wouldn't cause a cat code, or running rich- if anything it would run lean until the PCM added more fuel to compensate, and then it would go back to normal again. IMO the shotgun approach to just replacing parts hoping to fix the problem usually doesn't work that well.

I didn't think any montes came with a HUD? I thought it was just GP's, vettes, and some caddys...

 

No the monte's didnt come with HUD. I think what he means is the display on the roof right where the sunroof controls are at.

 

using a half a tank in 100 miles says something, that car shouldn't use that much in 100 miles.

 

My point is thats an awfully broad generalization off a tiny gauge with no numbers. What if it took another 150 miles to drain the tank to where he normally refuels, and he ended up only having to put in 14 gallons to fill it from there (thats almost 18 mpg or pretty normal for more aggressive city driving with lots of stops and such).

Its so simple to find out the actual MPG numbers- and they'd be so much more helpful in determining if he has an actual problem, or maybe just a harder drive than others.

 

true good point

 

not to mention, the monte guages arnt too accurate and i know of a few that just wobble. mine will go from a full tank to half in about 100 miles. but my fuel level resistance sensor on the fuel pump isnt good. and yeah, i called the controls on the roof heads up display..haha my bad. yeah montes dont have windshield display..lol

 

is your gas cap on tight? i left my loose one time and i got horrible gas milege but it threw a evap code. your egr can do that too. hope this helps :/