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Thread: Engine running lean through rev range

  
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    mantamagic's Avatar
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    Engine running lean through rev range

    Car went on the rollers the other day at Noble.

    Got good power (234bhp, 258 lb/ft) but they said it was running lean in the middle of the rev range and them came good at the end to give power figure.

    I know it's not the map, as I had the same lean problem prior to the map, so what can it possibly be?

    Plugs are good, fuel fine (optimax), so I can only presume it either AFM or maybe a lambda sensor.

    Any ideas how I can test/prove if it's lambda, afm or something else?

    Any ideas folks ?

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    jamesmurray's Avatar
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    it wont be the lambda sensor, as under full load conditions the ecu relies on base fuelling maps. could well be the afm

    jimbo
    ASTRA MK4 GSI TURBO
    WAS CS3 268bhp & 282lb/ft
    NOW CS4 279bhp & 336lb/ft

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    Would faulty AFM show up on Tech 2, as my car does not show any errors or did not last time it was checked when running lean.

    What are symptoms of knacked AFM ?

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    well, the afm has a major influence on the fuelling side of things, so poor fuel consumption, dips in the torque curve, etc would all indicate a dodgy afm. might be worth trying a new one. from what i can gather, its always worth keeping a spare. too bad they cost 100 notes though

    jimbo
    ASTRA MK4 GSI TURBO
    WAS CS3 268bhp & 282lb/ft
    NOW CS4 279bhp & 336lb/ft

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    AndyGSi's Avatar
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    The induction kit wont be helping too much either though, the hot air is considerably thinner than fresh air from outside, maybe the ECU is trying to compensate a bit too much, for the conditions of the air at inlet???
    Astra GSi Turbo, SOLD


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    As discussed Rob - sounds very much like the AFM, but if you have had the same problem for a long time then it might be as above - do you have an induction kit as Andy mentions?

    Shev's AFM showed a lean reading when it was being re-mapped, although it wasn't far enough out of tolerance for it to show the warning lights and therefore wouldn't show on tech2 as an error. Once they start to go though, they usually go pretty quickly, so I'm suprised that it has been like it for a while.

    In hindsight, maybe you should have taken the AFM from the missus' car to see if there was any difference? Running lean won't be doing your engine any favours.

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    I'll try cleaning AFM if it's possible with contact cleaner.

    Failing that I think Courtenay are cheapest at £99 unless anyone else knows of a cheaper source?

    Wifes car is 1.8 so cannot use that to test.

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    Worth a try with the contact cleaner I guess - although it could completely knacker it also! - not sure if LMF are any cheaper for the AFM Rob.

    Didn't realise your cab was a 1.8 - thought it was a Turbo....

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    Ordered new AFM from LMF.

    Cheaper than Courtenay as well, £99 delivered.

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    Hope it solves the problem Rob, but I guess you'll need to get to another RR (or tech2'd) to find out.

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