P0420 Cat efficiency
 

My CEL turned on the other night so when I got to work the next day I hooked up the tech 2 and it ended up being a P0420. First I checked to see if the HO2 sensors were working and the were working normally so then I cleared it.

I installed the zzp 3 inch downpipe with high flow cat around 1000 miles ago. Is it possible that the cat is failing already or is it just that our PCM isn't likeing it? I think its more along the lines of, my pcm doesn't like it, but could it be the cat. I would have thought that if it didn't like it it would have come up much sooner, but I could be wrong

I would be ok with just clearing it everytime it comes on, but my problem is my inspection is coming up in October and we have an OBD2 emmisions test so CEL= fail. Even though I do my own inspections there is no way around it. Clearing it is going to reset the rediness monitors and that will fail it too if more then 1 has not cleared. Do I need a pcm reprogram to eliminate the P0420 permanently, or should i email zzp and see what they will do? Thank you for any help

Hi LabNjab, Check back on your thread question 2 see what our expert tech member's post/suggest. Also, it never hurts to contact expert people like ZZP for assistance/infor.
Below are a few links you may also want to check out...Good Luck from `Space.
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I have the same setup and your stock o2 sensor is not setup to digest the new flow rate as being in tolerance.

I also had the same problem an installed an o2 emulator from ZZP. No more code and I have been through several inspections so far without a problem.

Exactly right.

The new downpipe flows much higher than the stock one, so your PCM thinks something is wrong when nothing is in fact wrong.

You can find someone who tunes 3800 engines and get the P0420 code deleted.
You can buy a canned PCM with the code deleted already.
Or you can try the O2 simulator that ZZP sells. (but if you were going that route, honestly Id just do a PCM for a few bucks more)

:rolleyes:..BlackSheep `Mike, it's great to have you back & helping your MCF Family 4-Sure : )

+++++Also super to see Moderator Montejass back online...`Todd it is so great to see you online with
your original User Name : ) Welcome back Home : )

Thank you everyone. I'll probably get a pcm from zzp unless I can find someone locally to tune it. I read that the o2 emulators don't work on 04's. I was planning on a tuned pcm eventually but looks like I'll get it sooner. I need to get the cooling fans to kick on at 180 so I can get them to delete the code at the same time...is there anything else I should have done to the pcm that would possible give better performance? Right now I just have a 180 t'stat, zzp down pipe and wizaird CAI

Just let them know what you have, and stress that you want the Monte Carlo Bin files.

Is DHP still pushing a decent software interface? I had not heard of the emulator issues with the 04's, wonder what the difference is between the 03 & 04 sensors?!?!?!

I opted for the simple most cost effective method to kill my O2 issue and went with the emulator; looking back it would have been nice to play around with the software out at the time to manipulate the PCM.


Thanks Space.... I've been poking around my usual MC sites looking for info; the ole Monte is getting up there in miles and starting to have some quirks.

3800performance says the o2 emulator will not work on 2004 vehicles. Looks like I'm going to get the custom pcm from zzp. I priced out dyno tuning locally and its at least $500. Now I just need to save up for it. The core charge is the killer, lol. If it wasn't for that I could order it today

Also check out overkill PCMs

http://www.getoverkilled.ca/L67CompProg.html

Or drop onto clubgp.com/newforum and see if you can find someone locally that will tune.

ZZP is excellent in refunding the core charge. I sent mine back and within 2 days I had the credit back on my card. (It only took 1 day to ship from my house to zzp)

That's good to know. I ended up ordering it last night and it shipped this morning. Hopefully it will be here by the weekend.

Will there be a noticeable difference in performance with the zzp 1.0 pcm?

Yes! Especially concerning your transmission- you will notice firmer shifts at higher RPMs that keep you in the power band longer. You'll also now be able to "skip shift"- meaning if you floor it in 3rd, you'll be able to downshift into 1 (factory PCM only allows 1 downshift- so from 3 to 2). This will put a smile on your face.

It also increases timing in certain areas and you'll notice a little increase in power.

Now that you've got a PCM, 3" DP, 180* t-stat, and CAI, it's time to drop pulley sizes! A 3.5 on that car would make it a whole new beast. :D

don't drop a pulley until you know your KR for sure!!!

It's different for everyone! haha

I can't wait to get the pcm now, lol. The no P0420 code is just an added benifit to the other benifits of the pcm, lol. As of now I'm running no KR so if I'm still running no KR after the PCM then I'll try a smaller pully once I can afford it and hope I still have no KR

Im thinking of perchasing the zzp 1.0 PCM Please let me know how it feels and how the install gose..

I will, I was hoping to get it by the weekend but the tracking number says i won't get it until tuesday

Alright Well let me know asap.. My cat is pluged and time to stright pip it from cat to the y pip :D and 2 flowmaster 40s or 44s.. I have not decided yet :(


Has anyone here tried the pcm From Overkill ?? Its seems to be a little cheeper at 204.00and 100 back for core = 104.. TOTAL.... zzp 99.99 + 125 for pcm and core.. + 20.00 extra for 2005 MC. and 10 bucks extra for 420 code delete Looking at 254.00 - 125 core is = 129.99 soo almost 30 bucks cheeper.

The core charge that is $125 is the Grand Prix 2004 & up (they have a different engine set up), you have to select 1997-2003 $75 core.

Got it in yesterday and installed it. Only took one try to do the security relearn. Man its like driving a new car. I didn't drive it much yesterday, but I did put on a few miles and the shifts a right where they should have been from the factory. No more lag when you step on it. I did a few 0-60 runs down a back road and it seems to pull quicker. Plus I'm no longer getting the light backfire I would occasionally get after hard acceleration. I'm going to wait until the weekend to put a hundred or so miles on before I send the old pcm back but as of now I'm impressed with the pcm.

Tonight I'm going to borrow the Tech 2 from work and make sure I still have 0 KR (I'm sure I do) and then start saving for a smaller pully.

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)

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.

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

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)

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

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

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