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High fuel trims/02s lean

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  • High fuel trims/02s lean

    Hi guys, got a 57 corsa vxr on 125k but about 40k on a forged engine and box rebuild.
    Very well looked after 6 monthly changes of oil millers cfs, filters and plugs.

    Its developed an issue where fuel trims are massively high like 30% om the stft, not left it on long enough for ltft to change. The o2 bounces around high near the .9.

    Theres a really loud sucking sound from the rear of the engine possibly in rocker possibly inlet manifold. When I remove the dipstick the sucking noise stops as its pulling in loads of air from the dipstick. same thing happens if I pull the hose leading from the rear left of the rocker cover (heading to my catch can)

    Any help or ideas on where to start be great!

    Cheers

  • #2
    I might be talking crap here but this rings a bell from years back about a PCV valve, which is like a membrane in the rocker cover having failed.
    Corsa C 1.4 (SOLD), Corsa D SRI Turbo (SOLD), Facelift Corsa D 1.4 SE (SOLD), Now Corsa E VXR...plus about 20 other non VXs

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    • #3
      That is exactly what I was thinking mate. Just the answer I wanted 👌 nevlocks got me one coming out today. Compression tested too and all were within 1 psi of each other so happy there!

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      • #4
        Ah good stuff, let us know you get on.

        I was trying to find the post i was think about but the search doesn't go back that far...i think it was the polish guy with the grey mapped SRI...Alizak?? that detailed it.
        Corsa C 1.4 (SOLD), Corsa D SRI Turbo (SOLD), Facelift Corsa D 1.4 SE (SOLD), Now Corsa E VXR...plus about 20 other non VXs

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        • #5
          Found it!

          February last year;

          https://www.vxronline.co.uk/forum/ch...er-please-help
          Corsa C 1.4 (SOLD), Corsa D SRI Turbo (SOLD), Facelift Corsa D 1.4 SE (SOLD), Now Corsa E VXR...plus about 20 other non VXs

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          • #6
            Nice one cheers mate! Well in true nevlock style it took him 22 hours 40 mins from me paying him to the rocker cover being at my door Haha! Popped it on and found a couple other issues while I was there, a really brittle breather behind the cover cracked removing it and the one way valve along that pipe seems to be failing. That being said new rocker is on. No more whistling. O2s are bouncing around as they should and fuel trims look happy!!! Cheers for the help mate.

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            • #7
              It was the diaphragm inside the cover, it was ****** causing vac issues inside the cover which meant it was pulling air from the inlet manifold and making me lean out like mad.

              For what it's worth though the cover was so old and brittle that lots of plastic cracked removing the diaphragm so if your cars old enough to need a need diaphragm for the sake of £50 just get a new cover.

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