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Diagnosing help please!

Discussion in 'Tuning' started by mboy, May 2, 2018.

  1. mboy

    mboy Member

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    Hi,

    My HSV has been running rough for a while, and I have been trying to track it down. I ended up getting a Mafless mail tune as I was adamant it was the MAF, but was wrong.
    So I replaced plugs, wires, a faulty coil, Fuel filter, coolant temp sensor, intake gasket and checked thoroughly for vacuum leaks.

    I have just got an ELM 327 and Torque pro (Probably should have done this first). I have no current codes and so have been looking at the live data.
    I have a Mafless tune, OTR and 2.5 exhaust, no Cats.

    Because of the SD tune (mafless) the LTFT is turned off so can not provide any LTFT figures.
    But I have been watching the O2 sensors and the Short Term Fuel Trims.

    When I turn the car on at idle the STFT starts down low and slowly climbs all the way up and fluctuates around 18% on both Banks, sometimes maxing out at 21%. Bank 2 is always a couple of % higher than Bank one.

    If I rev the car it will drop back down to 0 after I push the pedal, but starts climbing again.

    Alongside this the O2's are erratic, only fluctuating sometimes (like a good sensor should) and at other times they may sit at 0 or 0.1 (they don't sit on any other voltage). However, this does not seem to influence the STFT - at least not enough to bring it closer to 0%, they just remain high.

    Is this just bad o2 sensors? Or should I be looking into other areas like fuel pressure etc that could be causing a rich condition?

    Any help greatly appreciated!
     
  2. monstar

    monstar Naturally as-pirated

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    Sorry can’t help much but symptoms are of lean condition.
    Fuel rail / injector pressure delta reading?
    For both sensors to report same condition is likely IAT or MAP sensor (induction) issue like fuel air pressure leak else fault in fuel supply. Not O2. I’d take them as correct to start with.
     
  3. mboy

    mboy Member

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    Hey thanks for the reply!
    Just an update, I started the car last night to check the readings again and the STFT was sitting at 10% at idle and under 5% driving!! Really starting to confuse me!
    Oh and the readings werent the same on both sides all the time. For a period Bank 2 STFT was at 21% and the O2 at 0 for at least 30 seconds while Bank 1 was at 15% and the O2 bouncing fine. Then both went to 0.

    I've ordered online a fuel pressure tester kit so will look at that on the weekend and also a new MAP so will report back findings
     
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  4. mboy

    mboy Member

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    Fuel pressure is at 58psi. So that all seems fine.
    MAP reading on the tool seem to be all ok from what I have read on the net, and the intake vacuum was sitting around 20 at idle - which again seems all fine from what I read on the interweb.

    So I doubt there are any vacuum leaks or a fuel pressure related issue.

    The STFT still read like 15% and sometimes higher. When I start the car when it is warm, the O2's don't seem to start moving till the STFT's hit around 12-15%, then they start switching?? I'm at a loss?

    How do I do a Fuel rail / injector pressure delta reading?

    I hope someone here is able to chime in and help.
     
  5. 07GTS

    07GTS Well-Known Member

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    there is a delay after starting so u wont get instant feedback from the 02's, are u good at maths ? injector delta is the relationship between the fuel pressure at injector and the manifold pressure/vacuum so that the injector through it PW range stays consistent, if a single PW was used u would get more fuel in manifold vacuum then u would with baro pressure same as if u had 20psi fuel pressure and manifold boost at 20psi if u opened injector no fuel would come out so the ecu needs to know so it can adjust the injector flow rate to suit, when the trims are showing positive it means u are lean and they are adding that percentage of fuel back into it which is also why your 02's are a 0-0.1mv that means lean and the trims are maxed out so cant add any more, because u dont know exactly what the flash tune is setup like u should flash back in the stock tune and then take readings after a drive and see what its like, also when u removed the maf is it disconnected or still plugged in ? u will need the iat sensor for fueling to operate properly especially with mafless or did u fit another iat sensor
     

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