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2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #21
So the subi is at it again:confused:
Mainly trouble at idle. It feel like its 'leaning out' and then trying to 'catch up' to keep engine running. Then when I take off, very little power for a few seconds then all normal.
It also has started a strange noise when under heavy acceleration. Pinging?? It almost sounds like a rattle.
 

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01 Outback LL Bean
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2,439 Posts
Sounds like a failing fuel pump to me. Especially with excessive knocking now. Pump a fuel pump gauge on it.
 

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Registered
2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #23
So lets say the fuel pump is going. Then why are the only 'problem times' when I am stopped at a idle and the first few seconds when taking off, never when 'cruising'.

btw still no codes
 

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Somebody Else's XT
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14,433 Posts
Yeah I'm ready to chuck the fuel pump idea myself, as this has evolved. I did have similar drivability problems in my '98 until I found a couple of vacuum leaks.

To answer an earlier question, the front O2 sensor does not have to come from a dealer, but it does have to be an OEM unit. Avoid the universal fit types. I'm not sold on that being the problem, but I acknowledge that it could be. Only ever had to change one before. I haven't had to test one in a subie so I'm not sure what the measurement should be.
 

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01 Outback LL Bean
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2,439 Posts
Anytime you accelerate or create a low vacuum situation in the engine the fuel system is designed to flow more fuel. This is assisted by raising the fuel pressure which is controlled via a vacuum line to the fpr. Additionally when accelerating from a stop the engine rpm is low and O2 sensor readings are not as accurate and the engines ability to sense needed fuel is more difficult and response is slow. Once you are moving Rpms are higher and its easier for the system to adjust.

Put a fuel pressure gauge on it.
 

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Registered
2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #26
OK, finally something from the computer...misfire codes on cyl 1,2, and 3.
Pulled these pending codes a few minutes ago after the subi barely made it out of the driveway.

Looking for a fuel press gauge ;)
 

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2003 OBW 2.5L 4EAT
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860 Posts
Misfire codes are usually ignition related. How long ago did you change spark plugs? Check them out for wear either way. Another possibilty is that you have leaky spark plug tubes seals causing oil to get on to the ignition wires and spark plugs, but you will see that if you remove the wires.

If the wires are the originals, they might be worn and the part that attaches to plug might coming apart inside the wires casing.

Ignition coil is another possibilty, you can test it by misting water on it at night while running the engine and if you see it spark you will know its bad.
 

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Registered
2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #28
Could be, or fuel related?
It was idling down so far that it was barely running, then when I gave it more gas it couldn't keep the rpms up. Holding pedal so rpms are about 3K then vroom!! It would rev up like I floored it.
 

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Premium Member
01 VDC, 05 R Sedan, 06 BAJA EJ257
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15,466 Posts
Start over.

Check the amperage output of the battery. I don't know how you've been checking it but a battery can show 12 volts and still not provide enough amperage. Also check available amperage through the engine block and intake manifold. This will tell you if you have a bad or weak ground due to loose anchor, corrosion on an anchor or corroded cable within the insulation that is hampering ground conductivity.

Ground points are: on a bracket just above the upper starter bolt, left fender by the battery, on the intake manifold passenger side, straps that run from the engine to body/firewall, strap to the ABS assembly.

If the battery checks good, amperage output above 400, the higher the better, then check the alternator with a load on it.

You can check the fuel pump flow with a hose and a gallon bottle/bucket and a stop watch. The pump should flow upto 55 gph with no restriction, low end about 35. It can be toggled on via the fuel pump relay by jumping pins 30 and 87.

Fuel pressure can only be checked with a fuel pressure gauge, which is available at most parts stores in simple fashion that will work on your car. It should be approximately 43 psi at idle and increase with the FPR vacuum hose pulled. But you've already changed the FPR and hopefully from Subaru, so you are just checking the output of the pump.

Vacuum leaks will be tricky without a "smoke machine". You'll have to listen closely or use an accelerant to spray at vacuum connections, hoses and along the intake seals and gasket areas.

I've reread through the chain of events in this thread and a few things stick out. The lack of power then kicks in is an indication of one of the above listed causing the issue. The misfires can be caused by one of the above. A vacuum leak especially will cause what you are experiencing as a sudden change in pressure by opening the throttle, the ECM increasing the injector pulse to comply with the request by your right foot, the altercation of the timing to fire the cylinders properly to increase engine speed will all be thrown off by a vacuum leak. When there is a leak, it throws all the math off. As the engine rpm finally rises, the ECM has recalculated based off the input it gets from the AF sensor, and is trying to keep the engine running.

A bad battery will cause low amperage output and also effect the alternator output. Low amperage = Stupid ECM. It won't be able to function and control the actuators on the car with low amperage. It also follows that as the engine rpm gradually increases, the alternator output will bump up and provide more amperage for the ECM and actuators to function.

Low fuel volume to the cylinders during compression will cause detonation, pinging. If you are getting detonation, the air/fuel ratio is off either due to a bad pump, clogged filter, vacuum leak or poor timing. As the engine rpm increases, the ECM will increase the fuel injector pulse and alter the timing based on AF sensor and knock sensor feedback while calculating the TPS, ECT and MAF.

And again, this is based on what you have posted, but it sounds like its either a bad battery or a vacuum leak. I doubt its the fuel pump. Its possible, but on a low scale based on what you have posted.

If after checking the battery/alt, vacuum, cabling, fuel flow and pressure and you are sure there are zero issues with any of these, then move to the sensors starting with the MAF.

Good Luck.
 

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2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #30
k...good battery/alt, vacuum, fuel pressure (got my hands on a gauge today). Pressure was steady at 35 psi and 45psi with fpr vac hose off.

Now to check flow...
Where are pins 30 and 87?
I see no markings on the two round relays under the dash(driver side).
 

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2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
Joined
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19 Posts
Discussion Starter #31
It was idling down so far that it was barely running, then when I gave it more gas it couldn't keep the rpms up. Holding pedal so rpms are about 3K then vroom!! It would rev up like I floored it.
When the combo IAT/MAP sensor is disconnected, this fluctuation stops.
 

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Premium Member
01 VDC, 05 R Sedan, 06 BAJA EJ257
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15,466 Posts
That sensor shares grounds with ECT and TPS. Battery power is shared with TPS, PCM and TCM.

What temperature is the ECT showing when the engine is cold? After running it for a while? Is there a difference in the reading when the MAP is plugged in vs unplugged?

If there is a short in a sensor, it is likely it can be the IAT/MAP. Disconnecting it could be killing the short.

Attached is a wiring diagram.
 

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Registered
2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #33
After running like sh*t for the last 2 days, I finally got a P1137 code for the front O2 sensor. Picked up a Bosch OE part at Auto Zone this afternoon and so far all is back to normal. :29:
Sounds like Performance Suby's Forester!

Thanks again to all. Will keep you posted.

Nathan
 

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2001 OBW Limited 2.5, head job at 164k, rebuilt auto trans at 172k. 205K mi and counting 2003 Legacy L 2.5 head job and bulkhead harness repair 170k mi
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19 Posts
Discussion Starter #34
Still running like a champ.

So...front O2 sensors go bad long before they throw a code I guess.
 
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