I just got my first Mustang last month ('07 GT, Boss appearance package). It already had a Roush CAI & Flowmaster cat back. I just got a set of long tubes and an O/R H-pipe. A couple of my local muffler shops would not install it without the cats, but I found a speed shop that would do it. He warned me though, that I would run into problems with the front O2 sensors, lacking the proper back pressure, would give a false reading and make my engine run rich and idle high. Has anyone experienced this? I realize that I will have to turn off my rear O2's. does this have any effect on the front O2's. Has anyone had to retune after putting on long tubes and O/R mid-pipe?
It depends on the headers. It's more the location of the senors than the lack of back pressure. If you don't have a tuner, get yourself one, and ask your tuner to make any necessary adjustments for the longtube brand you're installing. Not to mention all the other benefits you get from a good tune, like better gas mileage, increased throttle response, and more ponies.
I have never heard of backpressure effecting 02 sensors. And the factory exhaust has almost no restriction anyway. The location of the sensor matters due to temperature and closeness to the engine, but I think they will be fine. I'd get a CAI/tune anyway though for the other benefits.
Well, it's not really backpressure... but lack of back pressure and faster traveling air could possibly affect it. But the real issue is the position of the sensors. I'm not sure about the whole air thing.
Thanks guys, My other question about the mid pipe is how do I get it smogged? I'v heard that you can't get a smog if the rear O2 sensors are turned off, others say that as long as the engine light isn't on it should pass. can someone clear this up for me? Should I get some cats and put them in?
I believe it depends on the state. Some states look for just CELs. Other states plug into the OBDII port and see if the sensors are operating.
The law varies state by state. They check to see that all of the I/M monitors are passed in the PCM. If your rear 02s are off, the Catalyst monitor will come up as "Not ready". Some states allow one monitor to be not ready, and will pass you. Some states do not, and will reject (not fail, but reject) you and make you come back when the monitor is ready.
