My 02 excursion had its back part of the cat break off but i had it welded back on and had a flow master put on at the same time. When i was towing i noticed that it was making a kinda whistling noise around 3k rpm and i just figured it was the flow master but now i have noticed my mpg drop about 2 from 13 to 11. I was wondering if i pulled out the cat and put in a strait pipe to test the theory that the cat is bad before i spend 400 bucks. I have heard that it will throw it a code because i have an O2 sensor behind the cat. Will this effect the engine mpg so defeating my test? Also what is the difference between a CA cat and the 49 state ones?

 

I didn't think 02 v10s were OBD2. But it shouldn't hurt not having the cat in. Just leave the downstream O2 sensor in place and it shouldn't bother it. As for the Cali cat vs normal cats, it's probably more restrictive. Over here in Mississippi we don't have to pass emissions so it don't matter what you run

 

My 2003 was also built for California standards and it is OBDII compliant as per the sticker in the engine compartment . It also has two O2 sensors before the cat (one for each bank) and one 02 sensor post cat .

As far as the functions of them ; first O2 sensor talks to the PCM and adjusts the lean/rich mixtures based on that O2 info. The second unit (post cat) tells the system if the Cat is functioning properly.

If the first one isn't working and second one can't detect change between both of the sensors,the PCM will be confused and the CEL light comes on .

Some other states (like , New York State where my truck is originally purchased) follow CA emission standards . These should answer your second question .

As far as your first question (cat test ) , you may want to clean your MAF sensor with an MAF cleaner , clean throttle and check your hoses (including notorious PCV valve 90 elbow) for deterioration/vacuum leak , if you have not done already . These are easier to start with .

Good luck,


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I'd be interested to know if it would be just a straight pipe or if it has to be bent.

 

It depends.

If it was a California or a "green state" vehicle, it's OBDII.

If the emissions label under the hood makes no mention of "California" or "OBDII", then it's a "Federal" vehicle and it's running an OBDI calibration.

I know this applies to the Super Duy trucks but I seem to recall reading somewhere that the Excursions were all OBDII compliant regardless of destination. Not sure, perhaps someone can clarify.