Hello,
Lots of reading but not much posting. You guys have been extremely helpful with information so I'm going to throw this out there and get some thoughts.

Vehicle: 2002 LS6 with cnc ported 243 heads, cam 232/238 on 115 with .559/.553, cold air set up, descreened mass air (std LS6). 6 speed manual, 2440 lb. car with 3.23 rear ratio.2000 Miata.

Original tune was done by Jeremy from Fastprom and car ran good with good driveability. Right at 400rwhp / 376 torque.

The original set up when tuned had conversion headers that were 1.5 inch shorties. A kind of get the engine to fit in the car type header. Since then Kooks has come out with a proper 1 3/4 inch full length header with 3 inch collector. When I swapped headers I made sure there are no exhaust leaks and O2 sensors are properly installed. I will say they are at least 16 inches down stream of the original set up but no wire extensions needed.

Now that I have changed the headers I have run into drivability issues. Under light throttle (7 to 15%) at low rpm (1200-1900) it is bucking really badly. With such a light car I had no problem going 45mph in 6th gear at 1200 rpm with steady throttle. Now it gets into a serious "trailer hitching" problem. I only have an OBD2 scan tool but the fuel trims are with in reason both short term and long term. Say between 2% and -3% on short term and last I checked +5 or so ltft. O2 sensor crosses back and forth between .5V as you would expect. IAT sits around 100* this time of year with 90* being ambient. I use a K&N cone style filter and used a new one when I put on headers. Thought it might have oiled maf but cleaning it made no difference.

Plugs look even across the board. It is worse in the heat of the afternoon on the drive home then it is on the way to work. Temps in the am are around the high 70's and on the way home low 90's. You can feel it almost want to do it in the morning but no question it's not happy on the way home. Right before it gets to bucking it feels like it is straining or "held back".

The question is; would changing to a proper header throw the tune off that much or could i be having a sensor or perhaps the maf starting to show a problem. Of course no codes of any type but I have no way of knowing what mil functions have been disabled.

If I left out anything pertinent, let me know. It's taking the driving fun out of this little hot rod. BTW 0-6 is 3.2 and 1/4 is 11.4 at 122. It will drive around most stuff on the street!!

Additionally, are there any decent stand alone data logging programs that might be helpful to diagnose this. The OBD2 scanner is limited at best. Thanks.

 

Does it do this cold or only when it reaches temp? But installing long tubes does usually require a tune, it will affect A/F at times.

 

Runs decent cold. Becomes more of a problem when warmed up and worse in the heat of day. BTW fuel pressure is good at 58 psi, forgot to add that. My understanding is that there are some settings in HP tuner that can be changed for the re positioning of the O2 sensors. Is anybody familiar with that?

 

[QUOTE=sbwrench;18288322]Runs decent cold. Becomes more of a problem when warmed up and worse in the heat of day.

Sounding more like its the O2's are the problem..Have you checked the plugs to see if they are black.

 

I have. They look fine. Typical fuel injected unleaded fuel grayish white with a light brown down on the porcelain. Replaced them to be sure. OBD2 scanner shows good voltage cross counts on O2 sensors. I know the scanner is far from a decent logger but it's all I have to work with right now.

 

But are the mv's moving around like a slot machine? they should be,

 

Yes, they are crossing back and forth through .5v at a rapid rate. Like I said I don't see anything jumping out on the scan tool. Any thoughts on a better way to diagnose what's happening. I don't want to spend more money on a tune is there is a sensor or something starting to go. In my experience they typically don't degrade. They either work or they don't. Anybody have any experience with maf issues?

 

Drivability really taking a crap now. 78 ambient on the way to work. Now I'm starting to see some big negative numbers popping up the STFT. The way it's deteriorating still feels like I'm getting a bad input but maybe its just really rich, although the feeling is more lean like. Anybody know of a competent person with HP Tuners in the Daytona Beach area? I gotta get a handle on this.

 

Just had a revelation. This really started getting bad when I put in a fresh set of TR55's. I ran the gap down from the out of the box .060 to .045. Could that be the culprit? Doing a search you sure see a lot of driveability issues that are plug related.