southsidescooby Posted April 14, 2004 Share Posted April 14, 2004 The Subaru dealer told me that Subaru of America is not willing to do anything else to resolve my detonation and lean running issues. I am following advice and running some SeaFoam cleaner through the fuel system to see if this might help. I am really interested in trying the modification to "condition" the rear o2 sensor's output. You stated that the resistor was installed "across" the sensor output. I am looking at figure WI-90 of the engine wiring harness and see the four pins to the sensor. Pins 2&3 appear to be for the heater. Pins 1&4 appear to be the input/output for the ECM. Did you place the resister in parallel or in series with the shielded output(pin 4)? Or did you install it across pins 1&4? Please clarify as I am anxious to try this fix! Thanks again for the help in making this car run correctly! Quote Link to comment Share on other sites More sharing options...
blitz Posted April 14, 2004 Share Posted April 14, 2004 It's been so long since I did this that I had all the underhood work soldered, taped, and tie-wrapped. I had to go back and refresh myself on all the specifics. The drawing that I worked off of was WI-83 (only drawing I had to work from). The connector you're refering to I believe is E25, and the leads that I dealt with were 4, & 3. 4 being the sensor signal, and 3 being the combined sensor signal ground and shield ground. These are the two leads that I tied the added resistance across (in parallel with the sensor, so it loads down the sensors output voltage). The sensor is a high impedance crystal that generates a small voltage and almost no current, not unlike a piezo. The remaining two leads (1 & 2) are the heater which is not involved. If you follow the rear sensor harness up to the engine bay, you'll notice that it becomes accessable at a 10-pin connector under the airbox. If you remove the whole plastic intake system including the airbox, you'll have unfettered access to this area. The color of the two wires I jumped across were an unshielded white (signal) which transitions (splices) to a shielded cable at that physical location, and and unshielded blue (ground). 100k is the best number to start with, then work your way down until the "iffy" throttle tip-in diminishes, then go one more for good measure. It takes several full driving "events" to log any numerical change, and I typically drove around for about a week with a given value before I rendered any assessment. The changes are very subtle as this ECU control mechanism is only a trim and not a master controller of fueling by any measure, but it was just effective enough to get rid of the lean tip-in that always creeped me out when pulling into moving traffic. I don't even think about it anymore. Don't work with the ignition on and don't apply voltages (ohmmeter measurement) to unknown ECU I/O. Normal operation proceedure. I'm anxious to see good results. Keep the group posted and if you run into a situation, don't do anything dumb, just ask. Quote Link to comment Share on other sites More sharing options...
99obw Posted April 14, 2004 Share Posted April 14, 2004 Across means parallel. It would go between the signal and the signal ground. FYI, adding seafoam to your fuel won't clean nearly as well as sucking it into the engine with a vacuum line. Others may be able to add more details. It sounds like your engine needs a good top end cleaning. Some good threads on top end cleaning: http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=5;t=001425 http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=5;t=001370 Quote Link to comment Share on other sites More sharing options...
southsidescooby Posted April 15, 2004 Author Share Posted April 15, 2004 Thanks for the clarification on the resistor placement. I just wanted to be absolutely sure as to the meaning and proper syntax of your instructions. Sometimes people's memeory tends to fade and details get dull. "Across" does generally mean in parallel with but I am not risking a $500 ECM on assumptions! The connectors involved on my current wiring print are T6 and T5/B19. I do not see connector E25 on this print. The wire for pin 4 is white and the wire for pin 3 is blue/white. I will do some further investigating this weekend and see how the car is actually wired. As for the Seafoam, I read the procedure for introducing it straight into the induction system. I will do this when I have the time. For now it was much easier to simply dump a can in at the last refueling! Best regards and many thanks. Quote Link to comment Share on other sites More sharing options...
blitz Posted April 15, 2004 Share Posted April 15, 2004 It just occurred to me that you're working on an '02 Legacy, and I'm working on an '02 Impreza. I'm thinking that the manual section numbers and connector numbers may not exactly correspond, although the circuit should be identical. Shoot me your e-mail address at blitz@flash.net and I'll shoot you back a pdf of the diagram page that I worked from with a few notes about the placement of the resistor, and you should be able to easily transcribe it over to your vehicle and drawing without any problem. Quote Link to comment Share on other sites More sharing options...
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