This is a Subaru Forester 2003.

The car start losing power after a few minutes on the road. And suddenly lost all power and is almost impossible to drive.

Already changed:

  • fuel pump
  • spark plugs
  • ignition coil
  • O2 sensor
  • fuel filter

The car had no check engine codes. The catalytic converter is new, less than 3 years old.

  • 1
    Welcome to Motor Vehicle Maintenance & Repair! Sep 19, 2018 at 2:06
  • 1
    When you say there's no check engine codes does that mean that there's no check engine light on the dash, or that you've read the OBD codes using a reader?
    – GdD
    Sep 19, 2018 at 7:24
  • 1
    Completely random guess, but did you check the earth straps. There should be a braided cable on each head, connecting the engine to the body. If one or both are missing, weird things can happen. They're often overlooked, and broken/torn off if the engine is removed without them being disconnected.
    – PeteCon
    Sep 19, 2018 at 14:05
  • Has no Check engine codes at this moment, a while ago had the p0447 code which was a broken cable and the p0420 that says Catalyst System Efficiency Below Threshold) bank1. And the O2 code but I already replace the sensor already. Right now doesn't show any codes Sep 19, 2018 at 14:20
  • 1
    Do you have any way to test fuel pressure ?
    – Pierre P.
    Sep 19, 2018 at 15:26

1 Answer 1


Catalytic converters can go bad pretty quickly when engines are out of tune. p0420 is possibly that.

The definitive test is a pressure gauge where the O2 sensor is.

If the compression on the motor is good (compression test) you need to look elsewhere. If compression is low on all cylinders - timing belt jumped a tooth.

Vacuum gauge will also give you an idea. If, at idle, the vacuum slowly goes to zero, you are no longer 'pumping air' and also points to a clog.

I had one motor loose power when 3 rocker arms jumped off (Chrsler 4.7, overhead cam) Compression check was weird, leak down test was also weird. I suspect owner didn't change the oil often enough and hydraulic adjusters (like lifters) were all coked up/clogged. Reved it too much when cold.... No noise from engine, no check engine line, just way down on power.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .