2000 Subaru Outback POOR POWER AT HIGHER RPMs

Tiny
KEVMCOLLINS
  • MEMBER
  • 2000 SUBARU OUTBACK
  • 4 CYL
  • AWD
  • MANUAL
  • 134,000 MILES
The car starts fine and can move on level terrrain with acceptable power, but going uphills it will accelerate fine in the 750 to 2500 rpm range in gears one and two, but once the engine approaches 3000 rpms the power fails and the car won't go any faster regardless of how much gas the engine gets. If I let off the gas there is enough power to move but no power for acceleration. Trying to give it more gas decreases power. There are currently no error codes( I have replaced the front o2 sensor and the catalytic converter, new plugs and wires). The intake manifold has a steady vacuum reading, but the compression test for all cylinders is around 175 psi except for cylinder two is at 150 psi. These readings are within specs. Any ideas? I have tested the MAP sensor and IAT sensors and they both pass. The fuel filter was replaced less than ten thousand miles ago.
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Saturday, August 16th, 2008 AT 12:42 PM

6 Replies

Tiny
KHLOW2008
  • EXPERT
Hi kevmcollins,

Thank you for the donation.

Your description of the problem seems like fuel supply is insufficient.
How long has this problem been happening and prior to it happening, any repair jobs carried out?
Did you check the ignition timing?
I suspect the TPS might be faulty.
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Sunday, August 17th, 2008 AT 4:00 AM
Tiny
KEVMCOLLINS
  • MEMBER
The Throttle Postion Sensor passes, reading.5 volts at closed throttle and about 4.5 at full open throttle. The enginge will rev up to 5000 rpms in neutral no problem. Under a load is when the situation gets funny. I drove around yesterday to try to throw an error code and got nothing. There is a clanky sound coming from the engine area when the car is slowing down or going downhill. It leads me to believe that there is perhaps an exhaust valve leak in the cylinder with low compression. The Subaru manual calls for 155 to 185 psi with no more than 5-10 psi between any cylinders. The haynes says 145 to 180 with no description on variances. Perhaps a crack that isn't big enough to backfire, but big enough to mess with compression ratios. No coolant in the oil and no oil in the coolant, so I doubt its the head gasket.
Also the ignition coil measures infinte resistance for its primary resistance check between terminals 1 and 2 and 2 and 4. The manual calls for around.6 ohms. Wouldn't it just not fire if this ignition coil did not have its ignitors built integrally to the coils. Some Subaru's don't have a primary resistance test for this reason, however I can't get confirmation as to whether the Subaru 2000 Legacy Outback Limited edition falls into the first or second category.

No repair jobs prior to it happening. It did need a CV joint replaced(front passenger side) which I did after this happened, along with a new fuel float level gauge(gas gauge was reading funny levels as it approached empty, now it reads well), oxygen sensor(which helped somewhat, now the problem is not as extreme but still there enough to be problematic going above speeds of 30-35 MPH) a valve lash adjustment(helped as well a little), and I did a vacuum test on the intake manifold which reads fine( a steady 22 inches with a drop to zero than around 25 back to 22 on a quick acceleration and drop to idle) but the compression check variation of 25 psi on the one cylinder has me wondering about an exhaust leak. All repairs were done after the car lost power. Only the O2 sensor and valve adjustment provided any noticeable improvements.
At this point I'm ready to pop off the intake manifold and look at some valves. Can you say valve job?
Any thoughts or ideas confirming or redirecting would be greatly appreciated.
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Sunday, August 17th, 2008 AT 9:00 AM
Tiny
KHLOW2008
  • EXPERT
Hi kevmcollins,

The difference in compression ratio could be due to valves leaks. Do a wet compression test to confirm if it is valve or piston rings.

Did you check the ignition timing? Could it be due to valve timing?

Any possibility of exhaust system restricted flow?
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Sunday, August 17th, 2008 AT 10:58 AM
Tiny
KEVMCOLLINS
  • MEMBER
I do not have an inductive timing gun to test timing on my Subaru, however, the engine does not sputter or backfire on accelerating in neutral. It rattles when the gas is let off and the engine returns to idle. Same with in gear, downshifting or slowing down using the engine produces the rattle noise which is fairly loud. I believe the timing is okay. It is the rattle and the low compression in cylinder two that seem to point to low power. I referenced my manual and there doesn't appear to be an egr valve. The vacuum test doesn't indicate a restricted exhaust. Whether the valve or rings the intake manifold will need to come off, so that is about where I am at. Any feedback would be greatly appreciated.
The camshaft position sensor tests okay. If I take the manifold off and no cracked valve, then the rings are at fault. I'll double check the compression test and do a wet test as well for confirmation.
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Sunday, August 17th, 2008 AT 3:55 PM
Tiny
KHLOW2008
  • EXPERT
Hi kevmcollins,

Regarding the rattling when decelerating, check the timing belt tension, it could be loose.
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Tuesday, August 19th, 2008 AT 9:21 AM
Tiny
KEVMCOLLINS
  • MEMBER
I'll check that. I leaned that thie ignition coil for the Isuzu Legacy Outback Limited Edition should have a primary resistance of.7 ohms approx. And mine is reading aver 40 megaohms right now. So in essence the timing is being effected because the coil is takig longer to fire due to the high resistance(which gets worse as the engine warms up, which matches the symptoms my car is exhibiting). So I've got an ignition coil on order and that should hopefully wrap things up for now.
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Tuesday, August 19th, 2008 AT 4:34 PM

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