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Thread: Mazda MPS Gen 2 - Very Negative LTFT on Idle -20 Help!

  1. #1
    iwannagiv is offline Full Member
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    Angry Mazda MPS Gen 2 - Very Negative LTFT on Idle -20 Help!

    FIXED: The Fix: I refreshed the oil and replaced oil filter - the correct amount and my LTFT fixed itself.

    I have been discussing this through the chat, but I think it is time for a post for all to chime in for some help.

    My car has a Cobb Stage 3 Performance Package installed
    https://www.cobbtuning.com/products/...package-w-v3-1
    This was running perfect for the first 8 months of owning it until below... Not sure if related.

    What has occured so far:
    I have replaced the worn spark plugs with a 1 Step colder NGK Plugs
    Replaced the oil filter + oil Penrite 5w-40 Full synthetic

    Symptoms Since:
    The start up from cold developed some stuttering for about a month.
    The car through a CEL P0172 Bank 1 Rich

    What I have done to try to rectify:
    I replaced the Spark plugs with stock spark plugs - got rid of the cold start stutter
    CEL reappears after driving a few days (about 5,000KM)

    Checked all piping for vac leak, found everything operating normally
    Cleaned the MAF & the Air filter multile times.

    What I have noticed (May or may not be related)
    Start on cold & let it idle brings LTFT down to about -9 and STFT in positive which in turn will make the LTFT change closer to 0.
    When I drive for about 10-20M and the water temp is 90degrees+ the STFT goes into very negative it drives the LTFT to -20 and STFT still goes about -8 which again in turns makes the LTFT more negative the more I let it idle after driving.

    I no longer have the AP as this was misplaced prior to me purchasing the vehicle, I have an OBDII connector (icarscan) which lets me monitor almost all sensors live and can potentially log whatever need be.

    So please anyone with any steps to rectify please let me know, if anyone in Sydney can look at my car I am willing to pay for time + rectification.
    Last edited by iwannagiv; 20-12-2017 at 11:33 AM.

  2. #2
    Nexus's Avatar
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    I can't speak with the confidence of a service agent, but
    If it's not showing knock retard even though it's pulling wads of fuel out, then I'd imagine it's actually running rich
    Faulty O2 sensor returning out of spec measurements could have it thinking it's too rich, having ECU attempt usual corrections but throw CEL when it can't be brought into line.
    Likewise a MAF sensor fault could have it actually running rich if it's reporting a higher airflow than actual.

    So...O2 returning measurements indicating it's richer than actual
    Or MAF returning measurements indicating higher airflow than actual.

    I think the spark plugs are a red herring in terms of the CEL. Definately that will have gotted rid of the cold stutters, but wouldn't be resulting in too rich CEL

    If it's got a cobb tune on it that tune might be inappropriate for you MAF housing. Is it an OEM airbox and MAF housing?

    If it's an OEM airbox and unknown tune I would immediately put a stock tune on it. Without the AP on hand I think that's a trip to Mazda, OR flash to Cobb's default mazda OEM tune with a replacement AP.
    I'm imagining previous owner parting out mods (such as an aftermarket intake and MAF housing) - removing the mods but not having the AP to return it to stock tune. That might account for MAF calibration being wrong.
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Federal RS-RR - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - 2XS turbo manifold - Hypertech tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - PC based GPS and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

    "Lipstick" 2013 Velocity Red MPS 3 - 18x7.5+48 Enkei RPF1 -225/40R18 Federal RS-RR - CPE TMIC - COBB inlet - CPE stg 2 mount - COBB Stage 1 98 octane tune - COBB shifty knob - 2XS short shift.

  3. #3
    iwannagiv is offline Full Member
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    Hi thanks for the reply.
    The Old owner did not part out anything from the car, the ap was just missing as I bought it through a third party (set price auction). I believe someone from the auction took the ap not knowing what it was, leaving behind the ap cable (labelling it AUX chord)
    The intake is the Cobb SF Intake. It was running absolutely fine for 8 months that I had it.
    I will check knock retard on next drive and see how that goes.

    I will try to source a MAF sensor and O2 sensor for testing before I blow couple hundred bucks replacing parts that aren't really faulty.

    Something I have notice though is that I do smell petrol fumes on idle, this was when I first got the car but I struck it out as the car didn't have a muffler it was straight through COBB twin pipe. I have since replacee the pipes with a stock muffler which made the car very quiet.

    So if anyone has a spare MAF or o2 sensor I'd like to throw some money to let me test on my car to find this stupid problem

  4. #4
    Nexus's Avatar
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    Yeah 8 months of normal means something has changed. Petrol fumes from exhaust at idle suggests it's immensely rich, and o2 sensor won't do that. I think perhaps your intuition was right and the MAF is out of whack. They are very sensitive - cleaning them can be risky. That's probably best place to start.

  5. #5
    iwannagiv is offline Full Member
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    I have been monitoring the STFT & LTFT all week and found something funny going on.
    On idle with brakes pressed in STFT goes more -negative. If i pump the brakes the STFT starts going positive & the more I pump them the more positive it goes I managed to pump it to +25 STFT, when I stop the pumping the STFT starts dropping and going into negative again.

    I am going to check the brake booster for any leaks or whatnot however I have not noticed any loss of brake power., do you think this might be related? Can someone try pumping their brakes on IDLE and monitor their STFT if it goes really positive while pumping? Give your leg a workout and let me know!

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    Gamboi is offline New Member
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    Ive got the same problem. Ive got full intake on stock tune. Had a real bad miss idle from day 1. Noticed stft fuel trim -10 at idle. Tried pumping the brake peddle and it goes up to 25. Have you ever figured this out?

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    Nexus's Avatar
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    Quote Originally Posted by Gamboi View Post
    Ive got the same problem. Ive got full intake on stock tune. Had a real bad miss idle from day 1. Noticed stft fuel trim -10 at idle. Tried pumping the brake peddle and it goes up to 25. Have you ever figured this out?
    I'm thinking brake booster vacuum leak?
    When you get on the brakes the booster leaks (sucks additional air in - STFT goes positive
    When you are off the brakes if doesn't?
    "Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Federal RS-RR - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - 2XS turbo manifold - Hypertech tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - PC based GPS and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.

    "Lipstick" 2013 Velocity Red MPS 3 - 18x7.5+48 Enkei RPF1 -225/40R18 Federal RS-RR - CPE TMIC - COBB inlet - CPE stg 2 mount - COBB Stage 1 98 octane tune - COBB shifty knob - 2XS short shift.

  8. #8
    iwannagiv is offline Full Member
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    Hi Guys,

    Sorry been very busy setting up my business - back to MPS now.
    GAMboi - if you changed your Intake on stock tune you will need to do a MAF Calibration with an Accessport for this tutorial: MAF Calibration Tutorial - Mazdaspeed Forums
    Pumping the brakes runs the car lean on any car I tried.

    HOWEVER: I figured out my problem. The issue is when I my mechanic did a service I believe he put too much oil which I eventually drained little by removing the Oil filter and putting it back in. However I believe the damage to the oil had already been done and it had a very strong fuel smell - the oil that is.
    The Fix: I refreshed the oil and replaced oil filter - the correct amount and my LTFT fixed itself.

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