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After replacing the engine in a 2007 outback 2.5l. The engine starts fine warm and cold. The engine has plenty of power cold but loses power as the car warms up. I've been swapping sensors and even the throttle body, one at a time. No changes. No codes Help?

EDIT: (Additions from comments)

Replaced the EJ253 engine in my 2007 Outback with a known-good running engine from a 2006 Legacy EJ253 mated to a 4EAT. I switched the keeper on the timing belt, and added the flywheel, and mated it to a 5MT.

The engine starts fine warm and cold. The engine has plenty of power cold, but loses power as the car warms up. The power loss seems to get progressively worse the warmer the engine. No codes.

What I've tried:

  • Swapping Sensors
  • Throttle Body
  • Knock Sensor
  • New Spark Plugs and Wires
  • IAT Sensor
  • Dropped Exhaust Manifold
Pᴀᴜʟsᴛᴇʀ2
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Clayton Guinn
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1 Answers1

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Pay particular attention to the temperature sensors, the IAT (intake air, likely part of the mass-airflow unit and the ECT (engine coolant temp).

A decent code reader will allow you to monitor these and see if they go out of whack.

Also, see if the problem occurs when the vehicle changes from "open loop" (cold baseline) and "closed loop" (using feedback from the O2 sensors). You can also see this on a good scanner that has "PID" parameter display capabiliity.

Subarus also have a hyper-sensitive piezo knock sensor that can cripple timing (and power) when going into closed loop, without throwing codes. This is often caused by overtightening. Mere inch-pounds are sufficient. Cranking down on this sensor makes it edgy and causes a huge retard of timing along with an associated loss of power. It's a two-wire donut thing with a 10mm head bolt on the engine block, under the throttle body area on the driver's side.

SteveRacer
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