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-   -   P0420 Cat efficiency (https://montecarloforum.com/forum/headers-intake-exhaust-13/p0420-cat-efficiency-15566/)

ChibiBlackSheep 09-02-2009 09:15 AM


Originally Posted by labnjab (Post 156368)
What would I be looking at for horse power estimates with my current mods with and without a smaller pully?

Honestly without the smaller pulley you aren't gaining much on the HP scale.

But once you drop that smaller pulley (if it's safe) you'll be pulling that more air and using it effectively and you will have a good jump in HP.

Shoot for the basic supporting mods for a 3.4 and you should be very happy with your HP. (though without a fully custom tune, I would probably just do the supporting mods for a 3.4 and then sit on a 3.5)

labnjab 09-02-2009 11:21 AM

Looks like its more mods before a pully. I just took it for a drive with the tech 2 and I'm getting 2-3 degrees KR just before and just after the 1-2 shift at WOT. Its only for a few seconds, but its there. I'm not getting it any other time except there. I'll start saving for a front PLOG and rockers before a smaller pulley.

ChibiBlackSheep 09-02-2009 11:30 AM

I would look into changing your spark plugs also. Don't forget when you mod an L67 it's good to change the cold step rating on your plugs.

Try getting a set of Autolite copper 605s put on, along with the 1.9 rockers and PLOG.

(pro-tip on the plog: no need to buy a gasket, the stock metal gasket will re-use with no problems)

labnjab 09-02-2009 11:36 AM


Originally Posted by chibiblacksheep (Post 156448)
I would look into changing your spark plugs also. Don't forget when you mod an L67 it's good to change the cold step rating on your plugs.

Try getting a set of Autolite copper 605s put on, along with the 1.9 rockers and PLOG.

(pro-tip on the plog: no need to buy a gasket, the stock metal gasket will re-use with no problems)


Thank you, I actually replaced the plugs after doing the CAI and down pipe with NGK v-power coppers that were a heat range cooler. Thank you for the tip on the plog gasket, that will save me some cash

ChibiBlackSheep 09-02-2009 11:39 AM


Originally Posted by labnjab (Post 156451)
I actually replaced the plugs after doing the CAI and down pipe with NGK v-power coppers that were a heat range cooler.

I wonder if those are just a step TOO cold for right now until you get the other mods in... either way you'd be getting the other mods though :)

Just work on getting those and then hopefully the KR is gone.

And no problem about the Plog gasket... I actually just put mine on. the gasket is actually going to stick to the motor, not even the front exhaust manifold, so you don't even have to transfer it haha (just remember to take the dipstick tube out before you think about moving the old exhaust manifold, and remove the 2 front crossover bolts first)

labnjab 09-02-2009 11:55 AM

Now Its just a matter of coming up with almost $400 for the plog and rockers, lol. Probably not until the first of the year cause I gotta register this car next month and I've been dreading that since I bought it. I'm thinking that will be close to $250:eek: I've also gotta get a set of snow tires/ wheels and remote starter before winter.

At least now I can get it inspected with the P0420 code gone and can enjoy the other added benefits of the pcm. Thank you

ChibiBlackSheep 09-02-2009 12:56 PM

If you have KR try to either not go WOT until you get the mods... or really try to pinch a few pennies so you can get those mods quicker :)

labnjab 09-02-2009 01:52 PM


Originally Posted by chibiblacksheep (Post 156473)
If you have KR try to either not go WOT until you get the mods... or really try to pinch a few pennies so you can get those mods quicker :)

I had to pinch just to get the PCM, lol. I'll keep my foot out off WOT, I usually do, even when passing. I'm wondering if I should test again.

I remember now that it looked like my evap was running a test and the purge was opening while the vent was opening and closing even at WOT, which would cause a vaccum leak or a rich condition depending on if it was open (lean) or closed (rich). I wonder if that would cause KR. I'm gonna test again tonight just to be sure

labnjab 10-12-2009 07:51 AM

Just an update, I got my inspection sticker no problems and no more check engine light. I've love the new pcm, especially when passing or merging onto the highway. Its like a whole new car. I also love that the engine temp now stays at 180 ish instead of jumping up to 200 at idle because the fans are now kicking on at 180

Hopefully I'll have the rockers and PLOG by Christmas, I get a weeks pay Christmas bonus and get to cash in my unused vacation time which will give me plenty of extra cash to get what I need


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