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Thread: Diagnosing rich AFR and misfire

  1. #1
    Garrett booster
    Join Date
    Jul 2015
    Location
    Kansas City
    Posts
    58

    Diagnosing rich AFR and misfire

    Hey all, I posted this on Facebook without much help so I figured I'd come here.

    I've converted my 1989 Daytona ES TBI auto to a kinda-sorta 2.5L T2 setup. Here is the run down on what the car is to give an idea.

    Tune:
    Unaltered BoostButton T-SMEC_25_ATX_S-II cal

    Engine:
    2.2 Block
    2.5 Crank
    2.5 .030" turbo pistons
    T2 rods
    782 unported head
    ARP head studs
    '89 TBI cam
    3.3 valve springs (with proper spacers)
    PT lifters (with spacers)

    Trans:
    Stock and very tired A413 from the TBI motor. Stock torque converter and everything.

    Exhaust:
    T3 57 trim turbo
    2.5" v-band to straight through 3"

    Fuel:
    255lph pump
    Stock one piece fuel rail and reg
    T2 injectors

    Intake:
    Stock 1 piece
    Stock 1 piece intake TB (46mm?)
    2.5" intercooler piping
    Big ol' eBay MR2 style intercooler

    IDK if this is against the rules, but the build thread is on a separate forum. If you'd like to know more about the setup:
    https://www.thechicagogarage.com/thr...ersion.174531/

    Any ways:

    I'm having an intermittent issue where sometimes the car will rich pig rich until it warms up, but will have the same symptoms regardless of the AFR. The picture of the MPScan shows about where the car sits sometimes when it's idling in neutral after it's warmed up. But sometimes that AFR will bounce from .2 to .9 rapidly, at which point the car breaks up hard with RPM increase. This also weirdly causes the turbo to spool up in neutral with RPM increase, I can build about 5lbs of boost on a 57 trim turbo. This makes me think timing is acting up or an injector is just hosing fuel into the exhaust.
    TPS reads fine, coolant is reading fine, I assume the O2V is correct since it's a new sensor.

    I say it's intermittent because the video shows how it was running.

    Initially I had a 58mm throttle body on the car, which would cause the neutral revs to hang for a second or so then fall back down. It was also having a small misfire while revving in neutral, so I figured lets swap the TB out for the stock one and see what happens:


    You can hear the misfire that it's always had, but the revving and everything was sooo much cleaner than it had been.


    Now, come to today where there has been 0 changes to the setup and it is now pegging the AFR gauge rich and bogging hard.



    You'll notice the wideband and the narrowband aren't really lining up right. It's also building crazy amounts of boost in neutral (especially for that size of a turbo), which makes me believe the timing is retarded or it's pig pig rich. Looking at the tune I flashed the anti-lag/launch control is disabled.

    Any ideas on what to look at?

    When I have moment I'm going to verify full pressure, last time I checked it was about 44psi at idle and went up to 58 when you revved it to 0 vacuum. I believe that's perfect but I may be wrong.
    I also need to verify ignition timing and cam timing, but last I checked they were dead on. Cam was at the normal marks and the distributor was set to 14 advanced with the coolant temp unplugged.

    Currently if you unplug the coolant temp while the car is running it will straight up die, so I'm not sure how I'm going to verify timing.

  2. #2
    turbo addict
    Join Date
    Dec 2005
    Location
    Mesa, AZ
    Posts
    7,332

    Re: Diagnosing rich AFR and misfire

    Quote Originally Posted by WarlockSyno View Post
    Any ideas on what to look at?
    Yes, this.

    Quote Originally Posted by WarlockSyno View Post
    Tune:
    Unaltered BoostButton T-SMEC_25_ATX_S-II cal
    In my experience the stage tune is no good.
    Since you're using 2 bar map and stock injectors, just use a stock 2.5L turbo cal to set ignition timing. Once your car is running ok, then you can start changing things to make your own calibration.

    http://www.turbo-mopar.com/forums/sh...-SMEC-codebase

  3. #3
    Supporting Member II Turbo Mopar Contributor
    Join Date
    Feb 2015
    Location
    toronto
    Posts
    1,655

    Re: Diagnosing rich AFR and misfire

    Quote Originally Posted by tryingbe View Post
    In my experience the stage tune is no good.
    Since you're using 2 bar map and stock injectors, just use a stock 2.5L turbo cal to set ignition timing. Once your car is running ok, then you can start changing things to make your own calibration.

    http://www.turbo-mopar.com/forums/sh...-SMEC-codebase
    A very wise suggestion. As a technical support troubleshooter, the #1 rule is to restore as many variables back to "known good" as possible. For example, the stock tune is known to work so this reduces this variable significantly.
    We will assume the ECU has zero codes and no vacuum leaks.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  4. #4
    Supporting Member II Turbo Mopar Contributor
    Join Date
    Feb 2015
    Location
    toronto
    Posts
    1,655

    Re: Diagnosing rich AFR and misfire

    Does the Map readout on MPScan close to pressure gauge on dash?
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

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