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Thread: GM 4.2L changing idle spark timing for piston slap

  1. #1
    Tuner in Training
    Join Date
    Jul 2020
    Posts
    16

    GM 4.2L changing idle spark timing for piston slap

    My 2002 4.2L has some slight piston slap when cold, nothing surprising, would like to try altering the spark timing to see if anything changes. I've just started using HPT and have only changed a small amount of TM and increased idle from 613 to 650 only to see if more oil flow would change anything. I suppose the change would need to compensate where the higher cold idle speed slows as the engine warms to a set ECT value, Would I need to change the hot idle spark as well as the warmup, that's where I'm not comfortable at tuning being a "rookie" to this. I'm watching as many videos and tutorials as i can. I will get a cold start/warmup log today.

  2. #2
    Advanced Tuner
    Join Date
    May 2006
    Location
    Seattle, WA
    Posts
    538
    Post your tune up, I'll take a look. I haven't tried to tune my P10 for piston slap at idle, my 4.2 has done it to varying degrees since it was new in 02.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  3. #3
    Tuner in Training
    Join Date
    Jul 2020
    Posts
    16
    PM sent. May need to start another thread as the piston slap is minor, but wouldn't hurt to get a good tune. There's not much to work with being a P10, however there's a few areas that influence spark timing and I don't want to move the values too much during testing.
    Last edited by dka56; 10-04-2020 at 07:43 PM.