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  1. #1
    Join Date
    Feb 2003
    Location
    Northwest Pennsylvania
    Posts
    706

    Default Multiple misfires - bad vacuum leak?

    2004 XC70 - 242,000 miles

    For the past few weeks I've been getting an occasional stumble when pulling hills in hot weather - i suspected plugs.

    2 days ago I was under the hood and heard a loud hissing from under the intake manifold - sounded like a vacuum leak - I moved some hoses and it got louder and softer, but I could not see anything.

    Today the wife brings it home and reports it is running very badly and the CEL is flashing.

    I pulled codes, and see
    P2187 - lean mixture
    P0300 - general misfire
    P0304 - misfire cylinder 4
    P0305 - misfire cylinder 5

    So it feels like the vacuum leak has suddenly gotten much worse - possibly because of me flexing the hoses. Where can I find a diagram that might help me track this down by feel - don't want to take off the manifold for this.

    Thanks.
    '04 XC70 (petrol/auto), Nautic Blue / Graphite, Premium, Touring, Boosters, Xenia Wheels w/235x60 Nokian WR's (wife's kid-hauler)
    '09 C70 retractable hard top convertible. Red with black interior.

  2. #2
    Join Date
    Feb 2010
    Location
    Virginia Beach
    Posts
    4,054

    Default

    For chasing down vacuum leaks, I use ether (starting fluid). IF the engine RPM increases when the fluid is sprayed, then you know that you've found the general area. It's not precision work, but it gets you in the ballpark. Be careful, ether is really flammable.

    Alternatively, you can use a propane torch, unlit, and the propane (also a fuel) will cause the RPM to increase. I've not tried that method, but it seems a bit more precise than the ether, and perhaps a bit safer.

    Garages use a smoke machine and pressurize the manifold to see where the smoke escapes. I've read that this can be done with a cigar. Which I might be willing to try just to enjoy the cigar...
    Current Fleet:
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  3. #3
    Join Date
    Feb 2003
    Location
    Northwest Pennsylvania
    Posts
    706

    Default

    Found the vacuum leak - obvious once I got in there with a flashlight - replaced the hose and got rid for the 'lean mixture' code - still getting the misfire codes.
    '04 XC70 (petrol/auto), Nautic Blue / Graphite, Premium, Touring, Boosters, Xenia Wheels w/235x60 Nokian WR's (wife's kid-hauler)
    '09 C70 retractable hard top convertible. Red with black interior.

  4. #4
    Join Date
    Feb 2003
    Location
    Northwest Pennsylvania
    Posts
    706

    Default

    Ended up being a single bad coil. Biggest lesson learned is that the misfire codes (0300, p301, 0302, 0303, 0304, 0305) are not accurate - I moved the coils around, cleared the codes and still got 0300 (random misfire) and 2 specific cylinders. It was only by unplugging the injectors one at a time that I was able to track down the one not firing - then I moved that coil again and the misfire followed. Went with the cheapest coil I could find just to get it running ($35 US) - may get a full set of Bosch's from FCP to avoid the next one.
    '04 XC70 (petrol/auto), Nautic Blue / Graphite, Premium, Touring, Boosters, Xenia Wheels w/235x60 Nokian WR's (wife's kid-hauler)
    '09 C70 retractable hard top convertible. Red with black interior.

  5. #5
    Join Date
    Jan 2012
    Location
    Newport, RI
    Posts
    258

    Default

    Would a misfire always cause the CEL to come on? Mine has been stumbling under acceleration or on hills, and I assume it's a misfire. However, no CEL yet.
    Silver '07 Adventure Series

  6. #6
    Join Date
    Feb 2003
    Location
    Northwest Pennsylvania
    Posts
    706

    Default

    I've had that twice - miss and stumbling at heavy throttle - especially on very hot days (upper 80's counts as very hot here) - at 81k mile and again at 177k miles - no CEL either time - both times a set of new OEM plugs fixed it.
    '04 XC70 (petrol/auto), Nautic Blue / Graphite, Premium, Touring, Boosters, Xenia Wheels w/235x60 Nokian WR's (wife's kid-hauler)
    '09 C70 retractable hard top convertible. Red with black interior.

  7. #7
    Join Date
    Nov 2017
    Location
    Tallinn, Estonia
    Posts
    1

    Default

    Simplist way to find vacuum leak is make smoke test with pressure not more than 0.3bar

  8. #8
    Join Date
    Oct 2017
    Location
    Lancaster, PA
    Posts
    56

    Default

    Yes, lean mixture could be vacuum leak, if it too bad engine will shudder and stop. To confirm the miss fire move those ignition coils to difference cylinders, if they're miss fire on new cylinders, replace the coils, if it still miss fire on the same old cylinders, replace the spark plugs.

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