I am going to buy the Apexi Auto Timer (pen sized). Anyway, I had one on my 2005 Evo and loved it for the battery voltage, o2 and a/f. I realize it's not the most accurate from what I am reading...but actually on the Evo is was pretty accurate. I also realize that I don't need one because the Turbo is liquid cooled and not oil cooled so no coking should occur. If anything for ME it's more of an eye candy thing, I think they are cool. So, my question is...what o2 sensor do I tap (FRONT or REAR)? The reason I ask is I read a couple threads that specifically say NOT to tap the Front because it can cause ECU problems. I am not sure how that conclusion was drawn because I tapped the Front o2 on my Evo and it worked fine. All it's doing is just reading off that wire if you tap it with a vampire tap. Any help would be appreciated. Thank you.
Well, you probably won't get any good info if you try tapping the front sensor, and you will get totally worthless info from the rear. Basically what happens is the front sensor is a 0-5v sensor, and once the afr gets around 12:1 or so, the readings will start to really skew. The rear sensor is a 0-1v sensor and the output is not linear, so any kinda of reading that you get off of it will be all over the place. I say save yourself some time and not worry about the afr. Russ
Yeah, the front o2 sensor isn't very accurate because of it's pre-turbo location and the high pressures it sees. I'm not sure on the 2.0L WRX, but on the 2.5L cars, the front o2 sensor is a full-on wideband sensor. The weird thing is that Subaru clipps the output of it at the ECU to stop reading after .75 lambda (~11:1 gas afr). However, the Enginuity guys have figured out how to overcome that, hehehe. I know of a few guys who are going to try to relocate it to the downpipe and are going to do some testing with their widebands to compare accuracy.
So are you saying that the o2 sensor reads from say around 14.6 down to 11:1 and will not go any lower? Or are you stating that tapping into the front sensor will not give you a reading over 11:1? Someone on NASIOC said that vampire tapping into the wired that goes into the ECU harness loads the circuit and can cause issues, anyone hear of this also?
Well, either way, the info you will get will not be very good. As the front sensor gets pressurized, the voltage gets skewed. That is why the ecu doesn't read off of that sensor when it cross's over. The rear sensor is a narrow band, so that is worthless also. The only way to get a good true O2 reading is by installing a aftermarket sensor someplace after the turbo. Russ
