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  1. #1
    Off the Xmas card list kapri's Avatar
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    Work with me on this ?

    Long loooong story but I'll pick out the important bits.

    Basically my A has never been that good on fuel . As I run it on LPG mostly I tend to forget as with LPG it works out normal costs.

    I bought a complete running Sierra and drove it round for about 6 months before pulling the engine and box that ended up being used in the A. Used to return around 40 in a run. Only mods to engine since being in the Sierra are 4 branch extractor manifold ,a high torque cam and K&N filter.

    I've used near enough the same cam in several other vehicles. All had/have PCV disconnected and blanked.

    POS .Cam with DGAS and crap exhaust manifold , 3 speed auto ,gave 33 on a run

    Pop. Cam with gas flowed head, injection unit , crap exhaust manifold , 3 speed auto gave 35 on a run.

    In the A ...cam, extractor manifold , 4 speed auto gives 22 on a run !!

    All have exactly the same overall gearing, same as that of stock Sierra / Cortina.

    POS had a vac gauge and tickover was 20".

    Obviously expecting 20" on the A but only makes 15-16" . It was slightly lower but a change in valve timing sorted that.

    Cruising light throttle " readings are always in 'poor' section of gauge.

    As soon as it drops into overdrive the " readings plummet ,even with the lightest of throttle.

    So I'm looking as to why it has a low vac reading as that is obviously a sign/ cause of the problem.

    All my knowledge ,and internet info agrees, that such a reading is normally ignition timing issues . However the injected unit is timed to 12 btdc (standard) and the ecu controlled timing is all working, verified with dial back timing light?

    MY other thought was a small vac leak somewhere so today I disconnected every vac pipe ( fuel pressure reg, modulator valve, torque convertor lock up and brake servo) DIRECT at the manifold and also used carb cleaner to check inlet seal , cracked fitting, split hoses etc. Nothing showing up at all . Typing this has just reminded me of one inlet fitting I haven't checked for leaks so will do that tomorrow ( idle speed control valve bolted to the inlet manifold).

    Any thoughts including stating the bloody obvious that I may have overlooked? No, I don't think fitting a crap exhaust manifold will fix it

    One thought , when I start from cold the " readings are only about 8 and pick up to 15 by the time it is warm. I presumed that as no choke flap and cold the water temp sensor enrichens the mixture and the idle speed control valve simply has to bleed more air in to keep it idling?
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  3. #2
    Off the Xmas card list kapri's Avatar
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    Just had another thought , haven't leak tested the seals around the injectors where they fit the inlet manifold, now on the list for tomorrow.

    As another thought/ pointer it returns the same MPG on both fuels.
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  4. #3
    Official RnS Addict v8ian's Avatar
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    Are/were they all autos, bigger cam making less vacuum and the loss of Vacuum with the auto playing havoc with the MAP sensor, causing timing issues and fuelling problems. or being injection, there is an engine management fault, Possibly Lambda, and going into limp mode?? Pure speculation BTW.
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  6. #4
    Administrator blackpopracing's Avatar
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    No idea Kev, but good luck with it.
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  7. #5
    Grown up? Never!
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    chaley is offline
    I'm with Ian on this, have you tried another ecu? Could be as little as a dropped sender?

    Chaley
    And on the 6th day Man created god.
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  8. #6
    Full Bloody Rebel! Mad Mark's Avatar
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    In comparison, the A has the aerodynamics of..........er..................a.......um........ ..................house brick!!
    If I wasn't meant to go that fast, the pedal would only go half way!
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  9. #7
    Official RnS Addict cptpugwash's Avatar
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    maybe the cam doesnt work as well with the 4 speed as your previous 3 speeds
    think the pointer is in the cruise reading....think it should be quiet high then
    maybe cam timing still, maybe that cam doesnt work as well with the comp ratio
    burnt out valve perhaps, vac advance not working
    just stabs in the dark im affraid
    Last edited by cptpugwash; 06-05-2014 at 19:46.
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  10. #8
    Rods 'n' Sods Junkie
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    Smokey is offline
    Hi Kev
    it could be either O2 or knock sensor if fitted ? If you can't check the
    diagnostic obd codes check the knock sensor voltage values
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  11. #9
    Official RnS Addict Perfect65's Avatar
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    "Bloody Obvious" but if the engine is as it was before - could there be a running gear issue - assume you've checked brakes binding or a drive train tight spot? These could explain a low vac when driving but as for anything engine side all those sensors and valves are not on my planet.
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  12. #10
    Rods 'n' Sods Junkie
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    Knock sensors are used to detect irregular vibrations
    With the extractor exhaust fitted it may have altered the resonance causing the knock sensor to try and compensate. Just an idea!
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