Smoking Under Acceleration

Discussion in 'Mazdaspeed 3 Troubleshooting' started by nunzi, May 25, 2025.

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  1. nunzi

    nunzi Greenie N00B Member

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    Location:
    Richmond
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    Year/Make/Model: 2008 Mazdaspeed 3
    Mileage: 150,000 on body, ~60,000 on engine
    Location: Maryland
    Concern: Black/blue smoke out of exhaust when accelerating from idle or after deceleration
    DTC's: none
    Modifications: CPE Catless DP, Corksport catback, Autotech HPFP, Stock diameter intake, CPE TMIC, 3-port EBCS, Action Clutch steel flywheel, new LUK clutch
    ECU/Tuning Software: Cobb
    Tuner: PD Tuning
    Is the concern intermittent?: No
    Can you duplicate the concern?: Yes
    Recent Repairs: Swapped engine for used JDM engine, turbo replaced with CW K04 last summer

    Hello everyone. I recently replaced my engine with a JDM engine from an importer in Maryland. Compression came back with all cylinders at ~175 - 185 psi, leakdown for all cylinders was less than 5%. The engine is smooth and pulls hard. I changed the engine because the old engine was down on compression and using a lot of oil. The mods I listed above were all on the old engine so the only thing that changed was the engine itself. The issue only presents when the engine is not cold. I am seeing a dark smoke when I give it any gas after idling (even just revving) and if I am decelerating and then accelerating again. I have driven the car about 300 miles since I changed the engine and there is no observable change in coolant or oil level. The cylinders and the spark plugs are dry.

    Not sure if this would help but under harder acceleration, there is quite a bit of black smoke that comes out the exhaust which I am assuming is fuel. I would guess that is a separate tuning issue but this also did not happen with the old engine on the same tune.

    My guess is valve seals but I know that is very uncommon on this engine. It also does not smoke on cold start. Any help is greatly appreciated!!
     
    Last edited: May 25, 2025
  2. Easter Bunny

    Easter Bunny Professional Engineer Motorhead Platinum Member

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    What oil are you using and have you had a tune revision since the swap?
     
    Easter Bunny, via a mobile device, May 25, 2025
    #2
  3. nunzi

    nunzi Greenie N00B Member

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    I put in fresh 5w30 Pennzoil Platinum before the motor was started for the first time. No tune revision yet as I didn't want to beat on a new clutch without getting some miles on it. This was also happening on the base tune and "final" revision from Will at PD. The tuning process was never finished originally because I was getting knock at high RPM which lead me down the rabbit hole of the engine replacement.
     
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