I replaced my entire exhaust with Milltek/Power Agency hardware. After about 10 minutes the CEL light came on and the engine hesitates/backfires at around 1200 - 1500 rpm.

Also, I cut out part of the stock air box (like the 997TT airbox) for more aire flow, and after running the car a bit I noticed a slight leak at the Milltek where the two mufflers connect to each other.

Finally, I changed the headers a couple of days before changing the cats/mufflers. During those two days I noticed a slight hesitation at low rpms, but no CEL. The hesitation was becoming less pronounced by the day I changed to the Milltek. Now it hesitates more and I have the CEL.

Any toughts? Will the computer adjust itself for the higher airflow? New O2 sensors? Fix the leak and see? The CEL/hesitation are driving me nuts!

 

sounds like you may need new plugs.

 

Don't play guessing games...get the codes read!

 

I would scan the car with an OBDII reader and see what the issue is. Do you have any type of programing? If the car is stuttering when you're on it at full throttle and around 4.5k rpms then your plugs need changing.

 

I know it's not the plugs (changed them already after I blew the originals after getting a GIAC flash). The car is actually stuttering at the lower rpms and "backfires" a little. Where can I get a code reader?

 

Durametric:

http://www.durametric.com/

 

don't count the plugs out, I have had plugs fail after just a few miles, a few times. although not with the turbo. but, you are more likely to blow a plug if you are changing and modding many things at one time. keep us posted what you find.

 

I will keep everyone informed as things progress. I'm going to get back under the car and re-check for leaks and that the O2 sensors are on corretly. I also plan to buy the Durametric OBD-II.

Questions: If I disconnect the batter for 10-15 minutes, will that turn the CEL off and/or will it ruin my GIAC computer flash? Since I now have more air flowing in and out of the car, do I need to upgrade my Stage 1 computer program to a Stage 3 or 4? Would that take care of the CEL?

 

check out your maf... if it's not consistant and kinda feel like your running over ralroad tracks' may be your maf. happened to me.. this is what itried first installed giac , nope , new plugs nope,and a bunch of small stuff. after all that fun stuff i cleaned my maf. and bingo it all went away and has not returned (a 10 min job) check it first it's free

 

The battery reset works for some codes...and not for others...depends on how bad. The battery reset will have no effect on the flash! No the flash (stage 1 is what you need for exhaust, DVs and some intake/filter changes).
We don't know what advice to give you on your CEL as you have not provided the codes. We will be happy to guess, but it is just that until we get some more info...make sense?

 

What exactly did you do on the aibox? May have fouled the maf. CEL are emissions related, always, on 996 cars. The combo of a leaking airbox(?), fouled maf and 100 cell cats will yield CEL's, as will any of those mods alone.
GL, check the codes.

 

I didn't even think of checking the MAF sensor. I changed my OEM air filter with a K&N, and cut a matching rectangle at the driver-side end of the OEM airbox for more air a couple of weeks ago. Would the K&N filter contaminate the MAF? It didn't feel oily when I checked it, nor did I oil it before putting it in the airbox. Also, since the added opening in my airbox doesn't have a snorkel like the OEM opening does, would it suck hot air into the system and reduce power because of the hotter air? I have read that this could happen. Keep in mind that I live in South Texas and the ambient temps down here hover in the 90's to 100's and I do 90% city driving.

By the way, thanks to all of you for your thoughts. I love this website.

 

Valley, The cut out of the airbox without a snorkel is a bad idea. You will create turbulent air flow and it will be HOT. Get a new airbox (see below with the second snorkel). And it probably is the MAF (for 1).

 

I second the MAF Idea.

I would like that airbox, but I don't it in Carbon Fiber. Regular plastic would be fine at the EVO V-Flow price or $7-800