hello, i recently bought a sc s2k with a Paxton sc and the car had a steady 14 AF at idle (which is ideal from what ive been reading) with the straight pipe. I recently put the cat back on cause it smelled like shiet without it and now im running lean with an AF ranging from 15-17 at idle. When im at wot it goes to 12 which i think is normal. So what going on with my idle? thanks for the help!

**sorry for typo in title***

 

can anyone help?

 

Could be since the tune was done with the cat off? Do you run a standalone ems? I don't think that is too terribly lean...your WOT in boost is 12...that is good. Lean in boost could be a problem...one that goes boom.

 

Where is the O2sensor placed. A cat will lean out the A/F ratio on the leaving side by a full point.

If your taking a reading after the cat it will be leaner than before the cat.

 

thanks for the replies, it was tuned with the test pipe, don't about the standalone ems.

They welded a spot for one of the O2s before the cat and the other sensor is in the normal position on the cat. The AF sensor is by the headers. Anyone know how to fix this problem? or why its running lean? thanks

 

What starrman was getting at is - with what engine management is it tuned? AEM EMS, flashpro, e-manage, what? If the car was tuned with the test pipe on, you may need to get it retuned if you plan to stick with the cat.

Slightly related, I went from a cat to a test pipe and my A/F was richer by at least 0.5. I did it primarily just to hear how the car would sound with the test pipe, but immediately swapped my cat back on. For reference, I idle between 14-15.3.

 

I have hondata

nitewing, your idle is 14-15.3 when your car is idle with your cat on? is that safe to drive? sometimes my AF jumps to 16 and i hear something that sounds like backfire when the car is idle.

 

The previous owner had it professionally tuned at a reputable tuner. I haven't had any backfire or idle issues.

 

you guys think its safe for me to drive around with 15-16 AF on idle?

 

The ideal AFR on all combustion gasoline engines is 14.7 (AKA stoich) however the computer is "active" running a closed loop circuit on our car, meaning it is taking in outside information to best maintain that AFR, which means it normally sweeps from 14-15.5AFR with the center target as 14.7. 16-17afr tells me something isnt calibrated right or you possibly have a 02 sensor going out. Chances are your tune was altered by the TP/Cat swap. At idle with engine under no load 16-17afr isnt serious short term, what’s most important is what the AFR is under cruising/light throttle and heavy/WOT throttle. You already said it was at 12AFR at heavy throttle which is good. What is it at say 20%-30% throttle? It should be around 13AFR there. Put the TP back in an see if the lean idle issue goes away for verification, if it does then you know what you need to do, keep the TP on or get the idle fuel adjusted for the cat and where that sensor is now located. And make sure before anything, that you have the 2 02 sensors in the right location and not reversed. The primary sensor goes closest to the engine, wile the secondary is normally run in the TP or cat.