Question about 1999 Subaru Legacy

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Subaru 1993 legacy rough start with backfire/missfire.

Once it runs for a bit it is fine,, but it is hard to start. I cleaned the fuel injectors but had no luck. I am thinking it might be a fuel filter or oxigen sensor.

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O2 sensors do not cause any kind of starting problems, what can is a dirty upper intake and loss of fuel pressure after the pump turns off.
Here is what I would like you to do, run a fuel pressure leak-down test on the system, to do this you will need a fuel pressure tester, this connects to the fuel pressure test port that is in the fuel supply rail that connects to the fuel injectors, it looks like a metal tire valve, the tester is about $15 at any Kragen or store like it, hook the tester up and verify no leaks, then run the engine and make a note of the fuel pressure reading, shut it of nd let it sit, the pressure should not drop more than 5 PSI overnight, if it does the fuel pump is defective as the check valve in the pump has failed, this allows fuel to drain back to the tank and creates a lean condition when the car is 1st started, result, rough running, long cranking times..

Posted on Apr 17, 2009

  • yadayada
    yadayada Apr 17, 2009

    also do the following:

    Here are some of the causes of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

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