Guest Posted May 25, 2007 Share Posted May 25, 2007 johnAWD - my car is stock engine wise mickeyd2005 - cool, thanks, I am wondering though if the sensor became "uncalibrated", and show correct value, yet in fact giving false reading; in other words without reference/redundancy no sensor can be trusted I am still trying to figure out my bad gas mileage and fuel dilution issues... since the theory of dripping injectors has failed (just had my dealer do leak down test on the injectors), I trying to investigate if "lazy/dirty" MAF and/or front O2 sensor can be culprits. I talked to some guy at local Subaru shop (Precision Tuning) and he suggested the car might be running rich and these sensors should be checked.... Anyway I guess I ask my LGT neiggbor to swap MAF and O2 sensors temporarily and see what happens... Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 25, 2007 Share Posted May 25, 2007 mickeyd2005 - cool, thanks, I am wondering though if the sensor became "uncalibrated", and show correct value, yet in fact giving false reading; in other words without reference/redundancy no sensor can be trusted In general, the front O2 sensor under steady state conditions should be fairly accurate or not accurate at all (broken). The MAF sensor is another story. It can easily be off a few percent based upon positioning or any other number of factors. It doesn't really matter though because as long as the front O2 sensor is accurate and there are no leaks, the LTFT (generated from front O2 sensor readings) should take care of any differences. Heck, the difference in energy content between west coast fuel and east coast fuel is probably more important than the MAF accuracy. To check fuel consumption, you may want to add a fuel injector duty cycle to my spreadsheet. Then in the macro, add it to the data to be sorted. You should then show a constant line for fuel injector duty cycle (y-axis) versus MAF (x-axis). We could then compare that slope to other cars. Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 25, 2007 Share Posted May 25, 2007 unclemat, there is a small possibility that you have a very small exhaust leak between the engine and the front O2 sensor. If that's the case, the front O2 sensor will think there is unburned air and will add extra fuel when in fact, it is not needed. If this is the case, my spreadsheet will show all positive total AFR correction across the board. Link to comment Share on other sites More sharing options...
Guest Posted May 25, 2007 Share Posted May 25, 2007 mickeyd - can you clearly specify what to log and under what conditions.... so I get all the data right. Thanks a lot! Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 25, 2007 Share Posted May 25, 2007 I wrote down the parameters to log here: http://www.enginuity.org/viewtopic.php?t=1871 Just add fuel injector duty cycle to the list of parameters. Use enginuity instead of ecuexplorer to log. You need the OL/CL status. You will need to datalog something like 3 to 4, 20 minute sessions. Drive like a grandma. Try to keep throttle movements very calm. Try to use the same tank of gas for all of the datalogs. Energy content sometimes varies. Link to comment Share on other sites More sharing options...
Guest Posted May 25, 2007 Share Posted May 25, 2007 Ok, any particular speed/gear? ....sorry for being a bore. Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 25, 2007 Share Posted May 25, 2007 Any gear and any speed. Just take it easy on throttle movements because the filter will delete any data is not relevant to closed loop steady state. If you drive like an @ss, you won't get enough data points. The best thing would be to drive a steady 10 mph, then 35 mph, then 70 mph. I just logged while driving to work. Go to work early so that you don't get stuck in stop and go traffic. Also, keep in mind that the rear defroster goes off after about 20 minutes so you have to click it again to start another log. Link to comment Share on other sites More sharing options...
stephenahood Posted May 25, 2007 Share Posted May 25, 2007 Are the 2 oxygen sensors interchangable? Someone running Stage 2 with the rear sensor doing nothing could move it to the front if they had an issue? Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 25, 2007 Share Posted May 25, 2007 No. The front is a Denso planar O2 sensor. It has 4 wires. The rear is a traditional two wire narrow band O2 sensor. It's way too slow to function in the front position. The rear O2 sensor is primarily for emissions and has almost nothing to do with normal operation of the vehicle. Link to comment Share on other sites More sharing options...
smkscrn Posted May 29, 2007 Author Share Posted May 29, 2007 Okay - CEL came back on today after about 2 weeks since it first came on. Been looking into replacing it and purchasing the part myself. The prices for the front 02 are around $100-115, is this correct? Is there any particular brand or whatever I should look into getting? Also - does anyone have any sort of tutorial or written breakdown on how to replace the Front 02? Trying to save a few bucks before my wedding next weekend.....yea, i know i know...another one down ! Joe Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 29, 2007 Share Posted May 29, 2007 It's like $100 on line. I think SOA just jacked up the price by about $10 recently. You can try PM'ing thekingofparts for a price+shipping. They're a vendor here. The front O2 sensor is a special Denso Planar O2 sensor with 4 wires. Bosch sells an equivalent for MORE money but I was told that it is a repackaged Denso unit. Your best bet is to get it from an online dealer. Replacing the front O2 sensor requires removing the front passenger side wheel and removing a plug to reveal the sensor. The wire harness will be obvious when you open the hood because of its bright color. Be careful not to damage the wires. I also recommend using a O2 socket wrench. Link to comment Share on other sites More sharing options...
smkscrn Posted May 29, 2007 Author Share Posted May 29, 2007 It's like $100 on line. I think SOA just jacked up the price by about $10 recently. You can try PM'ing thekingofparts for a price+shipping. They're a vendor here. The front O2 sensor is a special Denso Planar O2 sensor with 4 wires. Bosch sells an equivalent for MORE money but I was told that it is a repackaged Denso unit. Your best bet is to get it from an online dealer. Replacing the front O2 sensor requires removing the front passenger side wheel and removing a plug to reveal the sensor. The wire harness will be obvious when you open the hood because of its bright color. Be careful not to damage the wires. I also recommend using a O2 socket wrench. Thanks! Should I disconnect the battery or anything prior? So, pretty much just remove the wheel and the wheel well skirt, unscrew the O2 sensor with the wrench, then follow the wires to the wiring harness which will be under the hood (is there anything to remove to get to the wiring harness?) Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 29, 2007 Share Posted May 29, 2007 If the ignition is turned off, then all 4 wires should be dead. However, I'm pretty paranoid so I usually unhook the negative wire from the battery when working on any wires. Just open the hood and look for the bright yellow wire bundle in front of the firewall, on the passenger side, near the top. It's hard to miss. It will be zip-tied in two or three spots to prevent the wire from flopping around. Just squeeze the connector to remove it. Link to comment Share on other sites More sharing options...
edmundu Posted May 29, 2007 Share Posted May 29, 2007 I've swapped mine out w/o removing the wheel/tire. I just turned the wheel a bit, and it allowed plenty of space to get at the O2 sensor. Link to comment Share on other sites More sharing options...
smkscrn Posted May 29, 2007 Author Share Posted May 29, 2007 I have been hearing from speaking with some mechanics that depending on the EXACT code the ECU is sending, it is NOT certain that the O2 sensor we are talking about is the correct one to be replaced, even if the tech did say the "front O2". He also stated that there are about 5 (couldnt remember off top of his head) sensors and it would be horrible to replace the wrong one or put a sensor in there that is not intended for our LGTs. But in short - that the only real solution is to know EXACTLY what the code is, how to inturpret it and the correct part for the solution/replacement. That being said, I of-course panicked, scheduled an apt. at my subaru dealership b/c all of the local shops are just as expensive. Not to mention, have ZERO time to do this myself since my wedding is next friggin weekend... FYI - the mechanic i spoke with does not work at the dealership, rather through a friend of mine that is charging the same amount. HA. Exeter Subaru - $241.00 parts/labor. JC Link to comment Share on other sites More sharing options...
mickeyd2005 Posted May 29, 2007 Share Posted May 29, 2007 You can take your O2 sensor to Schucks and have it tested. Or you can pay $20 for a VAGCOM cable and datalog like we had originally recommended. Link to comment Share on other sites More sharing options...
LittleBlueGT Posted June 10, 2007 Share Posted June 10, 2007 The O2 sensor is easy to replace. Takes all of 5 minutes. I got mine from THEKINGOFPARTS at a much much much better price than the $250 they asking. My O2 sensor went bad because of the Perrin Headers and Rallitek skidplate combo. I didnt pay attention to clearance when I put them on. What exactly happened between the headers and O2 sensor? My front O2 just went bad this mourning and I have headers and the skid plate, but no obvious contact is evidence. Full tune of 68HTA, KSTech 73 MAF, Racer X FMIC and ID1000s................by the DataLog Mafia!!! Link to comment Share on other sites More sharing options...
FourMoBro Posted June 11, 2007 Share Posted June 11, 2007 The perrin headers have the O2 outlet like parallel to the axles. The sensor shoots straight out. I am unsure if I bottomed out on a gravel road, or if the bent up side pieces always hit. Basically the insulation on the O2 sensor wore off and the metal wires were contacting the plate. There was a nice dent in the plate, too! Link to comment Share on other sites More sharing options...
dj-phoenixx Posted May 9, 2011 Share Posted May 9, 2011 Hi, has anyone an logfile via romraider of the front and rear oxygen sensor. I think one of it is down. My car take 16,5l of 100km. After an run of 5 Minutes @ 100 up to 140km/h @ 6th gear the cell came on and he said P0546 EGT Sensor Circuit High. But i think one of the oxygen sensor is bad. Greets from Germany Marcel Link to comment Share on other sites More sharing options...
dj-phoenixx Posted May 9, 2011 Share Posted May 9, 2011 Hi, I'm back now from driving on highway. The fault code come back at 100km/h in 6th gear with A/C. Before was nothing. At Timestrip 64443 the MIL is ´coming. It looks like the rear oxygen sensor is faulty. Greets Marcelromraiderlog_20110509_194515.csv Link to comment Share on other sites More sharing options...
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