Tune after downpipe?
 

I'm getting ready to order a down pipe for the SS. Would a tune be needed after installation? I know a tune will be the best thing, but not in the cards yet.

Car already has the GMTU kit on it.

I can't speak for the GMTU but I have the Trifecta tune and I know with certain mods.. ie: Down pipe exhaust I will need to get the tune updated...I guess you could call your dealer and find out..

Depends on which pipe you get. The CIA catted down pipe that i have has never thrown a CEL and did give me some more power up top (based on but dyno) and helps spool time. BTW I'm selling it cuz Im buying Hp tuners which mean I can go catless and dial it in.

I ran a ZZP catless downpipe for 10 months before I tuned. Never threw any codes.

Once you have the gmtu, you can add a catted or cat-less dp. It you do throw a code, it will be p2147(o2). If cat-less make sure the pipe comes with a De-fouler, this will help prevent throwing codes, as the long tube pulls the o2 sensor away from direct exposure to the exhaust stream.

You should also notice some improvement, if the learn down is off. 09-10 have experienced problems with it not turning off after gmtu

CEL from a high-flow cat?
 

Hey guys,

Question - is the ZZP catted downpipe supposed to cause a CEL without a tune? I was under the impression keeping a cat was the "under the radar" way and not supposed to cause any problems.

Here's what happened - I installed my ZZP catted DP on my otherwise-stock SS a few weeks ago. I had it done by my mechanic friend at a local Caddy dealership. For the first 2 days, it ran great, no problems whatsoever.

Then, at the start of my drive back to Ohio from Chicago, I filled up the tank, and almost immediately after I got back on the highway the CEL came on. At first, I assumed that the gas cap was on incorrectly, but as I was in a hurry to get back, I didn't pull over to adjust it. When I got back to Dayton, I was pretty low on gas, so I filled up and made sure to replace the cap very carefully, not crooked or anything. The light went off, and i was a happy camper again.

For another day or so, it ran without any CEL, smooth as can be. Then the CEL came back on again, and for about two weeks now it's been on.

Is this normal for a high-flow cat? Granted, I haven't tuned, nor will I be able to for a while, but I thought keeping the cat versus going catless was the safe route to go. Any thoughts?

I run the Hahn catted downpipe I have yet to throw a code since July on an otherwise-stock setup.

... And there it goes again. Went to run a quick errand just now and the CEL was off. Should I be worried about this or just be happy it's off again?

I added the catless DP, open 3" tail pipe, cold air intake, put it on the Dyno & she was running so lean they wouldn't make the 3rd pull, when everything is installed check your A/F ratio.

How lean was it? What was your AFR at the time?