Should the sensor be installed before the split, or at the end, right where it bolts up to the cat?

 

before the split, you want the sensor to see ALL the gases

 

Opening the cutout will cause me to run rich, correct?

 

the cut out wont directly make you run rich, however when you open the cutout you might hit higher loads which are tuned richer...

in any case you should get a retune

 

I'm bumping an old thread I know, but I just had to laugh at these 2 J.A.'s that screwed up my DP.

I bought a QTP DP from a member on here with an O2 bung attached. Ever since I put on the QTP DP with a SP boost cutout, I would get really rich at WOT at 4K rpm to redline. The cutout would kick open at about 10psi around 3K rpm. I tried tuning it out, but I couldn't get it lean enough.

Then I had an epiphany. The freaking sensor is after the split, so when the cutout opens up, the sensor is reading probably less than 25% of the exhaust gases. I'm sure I'm really lean at WOT! So I'm laughing at the JA who sold it to me and to the other JA who didn't catch this, me. Luckily, nothing bad has happened. I have been getting some knock at high rpm's, but I'm trying to stay out of boost until I can get a new bung before the split.

 

I just looked at my fuel maps and I'm about 0.6 leaner now trying to get the AFR's right. I think I'll put in my rich tune from before the cutout to be safe.