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1996 Outback Legacy Emissions Problems - Need help trouble shooting

I am getting only about 13 mpg in my newly acquired Outback and am new to diagnosing these problems and need a little help with where to go without replacing everything. I did a OBDII read and exported the data to Excel : Test was initiated beginning at idle with engine warm (coolant temp reads 180-190 deg F). Idled for 1:34 (1 minute, sec)and the increased rpm to ca. 2000 rpms for about a1.5 minutes and then dropped rpms back to idle.

Mass Air Flow Sensor : Seems fine throughout the test reading steady at idle (0.4-0.45 lbs/sec) and increased (2000) rpms (1.0-1.15 lbs/ sec).

Timing Advance for Cylinder 1: 15 deg at idle and 44 deg at 2000 rpm (steady on both)

Short Term Fuel Trim: -25% at idle and increase in rpm, but up to 0% when rpms went from 2000 back to idle and fell gentle and steadily back down to -25%. Seems I'm running rich, but why?

Long Term Fuel Trim: Fluctuating from 26% to 27% at idle and constant at 27% at 2000 rpm

Intake Manifold Absolute Pressure: 4psi to 4.5psi at idle and decrease to 3.5 at 2000 rpm

Upstream Oxygen Sensor Voltage: Varies from 0-0.4v, but moreover 0.2 to 0.4v. It did increase to 0.5 after going from high rpm back to idle and then drop back to previous levels once at idle

Downstream Oxygen Sensor Voltage: Almost the same as the upstream O2 sensor, but about a 0.1v lower and looks like it had a time lag of 2-3 seconds. Does this mean my catalytic converter is shot?

Upstream Oxygen Sensor Fuel Trim: At -22% to -25% except when rpms drop from 2000 to idle and then it jumps up to -1.5% and then steadily decrease back to -25% in about 1.5 minutes

Downstream Oxygen Sensor Fuel Trim: Always at 0. I'm guessing that the car just doesn't register that parameter.

If I can find out how and where to post the charts, I will ( I can do it in PDF, Excel, or Word)

Thanks in advance....

Sparky

Reply to
Sparky19
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The manifold abs. pressure reading does not seem normal.

The vacuum reading at idle should be about 18" Hg (mercury), and normally the reading should be in the 1 or 2 volt range. The int. manifold pressure senson or its circuit seems to be out of whack.

Good luck!

Sparky19 wrote:

Reply to
AS

Yes, you are right - I didn't see that. I guess I need to test it with the key on and engine off to see if it reads atmospheric pressure correctly. If so that part is a good $200. Is there a way to fix that? I'll look at it tonight and see if I can't take it off and clean it if it doesn't read the right barometric pressure.

Thanks! I'll report back.

Sparky

Reply to
Sparky19

There have been folks who have used K&N type (oiled) filters and have needed to clean the filament to restore the MAF sensor function. But if you have a MAP then I dunno.

I wouldn't discount the possibility of also having a bad Engine Temp Sensor(not Temp gauge sender) - it can fail in such a way as to keep the ECU in 'cold engine/choke' mode which will produce very poor gas mileage/rich conditions.

Carl

Reply to
Carl 1 Lucky Texan

Today I replaced the MAP sensor with another and the problems still exist. MAP reads the same (about 4.5 psi - that's , but this time I took the vacuum hose off the MAP and it read 14.5 psi (Barometric pressure ). So it is reading right, it's just that the 10 psi difference is the manifold pressure (vacuum), right? And you're saying the OBDII data should be reading 9psi? Does Subaru have a different zero point for the pressure?

No K and N filter installed an the MAF is reading good - I even cleaned it to make sure.

Also when car is running, the OBDII says it's in a closed loop mode, so not that.

I'm still wondering about the downstream O2 sensor reading about what the upstream does. Catalytic converter?

Sparky

Reply to
Sparky19

Now you seem to have the proper change in the MAP reading reading (or was it a typo in the original message?). Remember that the map reads absolute pressure, so your 4.5 psi correspond to a vacuum of about 18 in Hg. Accelerating the engine should increase the pressure, not drop it as you stated in the original message.

The other sensors appear normal to me.

Have you tried the usual stuff? Tire pressure, alignment, air filter replacement, spark plugs condition, ignition wires resistance, engine compression? Is the tranny slipping, brakes sticking? Most of this stuff can be checked without replacing anything.

Good luck!

Sparky19 wrote:

Reply to
AS

Reply to
brian

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