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mightGETaSUBARU

maxed out fuel trims, rough idle, rear end dragging in parking lots AGAIN

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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 by mightGETaSUBARU

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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

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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)

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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.

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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.

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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.

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