Thread: Cat code question.

I have P0420 disabled in my car. Is that why I get sh1t for gas mileage recently? I was planning on a catless DP so I just did it when I had the HP tuners(me and some friends rotate). However, modding for the Bonneville has ceased. Will that one code being disabled cause the problem that is in the sticky in the tuning section? Before anyone asks, all the maintenance is up to par. The only thing I that I need to do is do a better job of cleaning out my TB, but I don't know how much that should affect MPG. The car always gets 87 from Costco with 10% ethanol in it. She runs perfectly and smoothly. I just got 16.7 in the city and I didn't cross over 2.5k RPMs in the last 5 days. :/

Thanks for any advice guys.

Do you still have both O2 sensors installed?

My car's exhaust system short of mufflers is completely stock. I have both sensors.

And yeah I plan on turning it on when I have the tuner in my possession but I don't wanna ask my buddies for it just for that one thing, especially since we don't live so close. Just testing the waters with you knowledgable guys on here first.

the diagnostic code they talk about in that tuning thread causes trouble when it doesn't recieve the "proper" signal from the rear O2 sensor. (a.k.a. removing the sensor or running a sim) the P0420 code is thrown when the CAT is running too far out of spec. A P0420 code will cause the PCM to go into limp mode, unless I'm mistaken, and will cause poor gas mileage. They are actually two different problems that cause the same symptoms...rich running engine and poor MPGs.

16.7 in the city is pretty good when you think about the the weight and gearing you have. If anything just make sure you have the cat disabled too not just under the DTC section but also in thle engine diag menu as well as cat over temp protection.

Thanks for clearing all that up. I turned it back on anyways. I'm just used to seeing 19-20 MPG but recently I guess being in a lot of stop and go traffic has murdered my mileage.

edit: dbl post

be 100% certain you dont have a leak cus i didnt think i did and couldnt figure out my **** mileage (7-9mpg) i threw some seafoam in it and seen it was leaking at the crossover and i couldnt hear it or see it otherwise. so i fixed that leak and did the spark plug non fouler trick on the rear o2 and now im getting 16-19 all city driving stop and go traffic
btw seafoam works wonders i run it every 3-4 months. last week my brother in laws camry was running like ****, idle was at like 1800 rpm abd just ran like ass, we tried changing everything to get the rpms down and no luck. we had got a couple bottles of seafoam when buying parts for ****s and giggle and as soon as i ran it threw 1/2 a bottle in the intake the thing dropped idle and started purring like a kitten

also what are your mods and what are you running for plugs tstat ect...

As far as the spark plug non fouler, basically it's just a metal tube which I thread into the exhaust pipe O2 hole, then thread in the O2 sensor on the other end right? Are there different lengths or what? I get the P0420 code after getting a Magnaflow Cat & 3'' Downpipe. Was wondering if maybe this could help a little. I'm trying to do a few small things before I have to bring it into a shop to figure out my high rpm misfiring and small idling issues. I'm going to try to seafoam first to see if that helps at all and find any leaks if there are any.

I looked up the downstream, it's an 18mm. So will this work? http://shop.advanceautoparts.com/web...on+fouler+18mm

Also, I'm getting code P0036 (Heated Oxygen Sensor, Heater Control, Circuit Bank 1, Sensor 2) I tested the heater resistance and it was about 8 Ohms. From what I read up on, that is about right. Any suggestions?

As far as the seafoam goes, I can just use the brake booster vacuum hose line for adding in the Seafoam slowly while someone holds the gas down aroun 2500rpms right? Then shut it off and leave it alone for 10~15min then start up again?

Originally Posted by nik12937

Just put your 2nd O2 in a spark plug non fouler or two to extend it away from the exhaust pipe. It will trick it into thinking a cat is lowering emissions since not all of the exhaust fumes are hitting the sensor anymore. It works for high flow cats, I'm not sure about straight pipes though.

Cheap alternative to an O2 emulator, especially on 04+ GP's where emulators throw codes.

not to hijack the thread, but my car does not have a cat so i am going to try the non foulers. are they all the same size? i plan to buy them on tuesday when my scanner comes in and read codes, reset codes, and then see what codes come back, inspection will be the following tuesday.

Originally Posted by jjmitch87

not to hijack the thread, but my car does not have a cat so i am going to try the non foulers. are they all the same size? i plan to buy them on tuesday when my scanner comes in and read codes, reset codes, and then see what codes come back, inspection will be the following tuesday.

you sir, need a cat or you will not pass inspection in the state of Mass. you now have till tuesday to get a cat put on the car.

MIL eliminators will not work? They dont physically search for a cat, at least not at any place Ive went to. At the very least I can see if I can pull some strings/get a favor.... heh

if they do a sniffer test you'll fail for sure. if they look you will fail, being mass is worse then NJ, here they drive over a camera, but dont really look at much. gas cap, obd2 scan, and look for the cat, and out the door you go.

it would be best to have the code tuned out, that way it wont show at all. those eliminators sometimes dont work with a hi flow cat.