June 23, 201312 yr well its happening again... not sure what to do.... rough idle, poor mileage, fuel trims are maxing out, then driving on a stop... what the heck is going on... http://www.ultimatesubaru.org/forum/topic/138678-98-subaru-legacy-wagon-is-getting-around-17mpg-after-headgasket-job-ecu-reset-used-to-get-almost-29mpg/?do=findComment&comment=1167133 Edited June 23, 201312 yr by mightGETaSUBARU
June 24, 201312 yr Author this sucks so much, I am going to burn through 200-300 in fuel this week alone... ideas?
June 24, 201312 yr Author I have not replaced the O2 sensor... I doubt it is mechanical (timing marks)... this issue cleared up and gave no issues for close to 2000 miles, even got around 27 MPG (mostly highway) on my last tank one thing I do know is the issue cleared up after reattaching the fuel pressure regulator...(long story) while doing I know for a fact my hands bumped into the main harness wiring and upstream 02 wiring... so I kinda think there might be a short in there somewhere. for giggles I unhooked everything last night and noticed he connectors felt oily... in fact it kinda looked like there may have been and oily type moister in a few of the plugs... which makes very little sense
June 26, 201312 yr Author ok got this off the scan tool today... not sure what it means exactly 02 Bank1 Sensor1 Rich-LN Sw Time Mod $E1 MAX 1.02 (s) MEAS 0.00 (s) MIN 0.00 (s) LN-Rich Sw Time Mod $E1 MAX 1.02 (s) MEAS 0.00 (s) MIN 0.00 (s) Min V For Cycle Mod $E1 MAX 1.275 (v) MEAS 1.275 (v) MIN 0.00 (v) Max V for Cycle Mod $E1 MAX 1.275 (v) MEAS 0.00 (v) MIN 0.00 (v) -------- 02 Bank1 Sensor2 Rich-LN Sw Time Mod $E1 MAX 1.02 (s) MEAS 0.00 (s) MIN 0.00 (s) Min V For Cycle Mod $E1 MAX 0.540 (v) MEAS 1.275 (v) MIN 0.00 (v) Max V for Cycle Mod $E1 MAX 1.275 (v) MEAS 0.00 (v) MIN 0.250 (v)
June 26, 201312 yr Those numbers don't mean much, just that the sensor is capable of producing a voltage signal that appears normal. Long term fuel trim is based almost entirely on input from the O2 sensor, Bank 1 Sensor1. Basically the front sensor in your case. Subarus maximum fuel trim adjustment is something like 27.5%. So if the trim is maxed out, the ECU is adding 27.5% more fuel than is normally needed for stoichiometric combustion. If the fuel trim adjustment is maxed out in the positive direction its because the O2 sensor is reporting a lean condition. The ECU is trying to compensate for this by adding fuel. If the sensor still reports a lean condition the ECU adds more fuel and more fuel until the sensor responds, which in this case is not happening. Either the front O2 sensor is faulty, or there is a leak in the exhaust between the cylinder head and front sensor allowing oxygen into the exhaust stream. Check for leaks. With the engine running have someone stuff a balled up shop rag in the tailpipe while you listen for any leaks up front. Leaks that affect the front sensor will be between the manifold and the front cat flange. Of you have no leaks replace the front O2 sensor, and reset the ECU to reset the fuel trims.
June 26, 201312 yr O2 reporting lean could also be from misfire, but I assume that it would throwing a code for that.
June 29, 201312 yr Author ok I need some help, I am loosing my mind here, I can no afford all the extra fuel costs, and I can not afford to take the car in I replaced the front o2 sensor, but it did not help so here is my QUESTION: What can cause ALL these problems??? erratic shift points and shift 'hardness' or softness (automatic) stutters at idle maxed out fuel trims fluttering/rough idle 12-15 mpg no codes at other times running just fine, with mid 20s on fuel mileage and smooth shifting my gut is now telling me the ecu/engine harness is buggered up some how.
June 29, 201312 yr My best guess would be a loose ECU ground on the intake manifold, or poor connection at the three main ECU harness connectors on the bellhousing. ECU ground is 4 black wires that come together to one eyelet and bolted either to the top of the manifold by the ignition coil or off on the drivers side rear of the manifold down low near the number 4 fuel injector.
June 29, 201312 yr Author I agree, I think its ECU related, bu I have cleaned and reseated the harness connectors several times, NO JOY
June 29, 201312 yr Author well I checked the manifold ground point, its not even tight.... man how did i miss that? going for a drive, cross your fingers
June 29, 201312 yr Author MUCH better, smooth/predictable shifts and trims are no worse than +/- 11% not perfect but not too bad
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