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Low Compression-What went wrong..?

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  • Low Compression-What went wrong..?

    So my car developed a slight misfire under load at the last track event. Only happened on the last couple sessions so I didn't think much of it. Ordered some new spark plugs thinking its just spark plugs. When I pulled the spark plugs they look like this: Cylinder 1 is the bad one, other 3 look normal. They have about 7-8K miles, 3 track days and rest street miles. They are NGK Copper plugs. Was running ~10psi of boost (stock S14 T28) at the track day and water temp stabilized around 210F coming out of the engine (never went above 215), and A/F ratios were low 11s.

    Car runs fine with new spark plugs but Cylinder 1 now has low compression. Based on a leak down test, it seems like it is piston rings, air escaping into the crankcase. Probably going to do a rebuild but just trying to figure out what went wrong.

    Only thing I can think of is a bad injector causing that 1 cylinder to run lean.
    Could it have something to do with the ignition coils?

    Thoughts?

    [IMG][/IMG]

    On a side note, here are a few laps from this event:
    https://www.youtube.com/watch?v=8_7VwkmtBto

  • #2
    Do any have specks of silver on them? If so, that's a sign of detonation.

    What's your tuning? I haven't seen an off the shelf rom tune I'd take to the track. Way too much timing generally to put up good dyno numbers, then you heat the engine up on track and it knocks all over the place. It's hard to hear because it's right on the edge of knocking, but it'll damage stuff over time.
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


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    • #3
      That top spark plug looks like it has specks on it just from the photo.
      Core4 Motorsports
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      • #4
        Yea, I can see it clearer now. Detonation. Either something wrong with the fuel injector, or an aggressive tune.
        '18 Chevrolet Volt - Electric fun hatch for DD duty!


        DefSport Koni Sleeve and Spring Perch Buy!!!
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        • #5
          #4 looks like it has small specs too.
          Originally posted by SoSideways
          I don't care what color they are as long as they are LONG AND HARD.
          '04 G35 Sedan 6MT- The DD
          '96 240SX- The Track Toy

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          • #6
            Ohman, this brings back bad memories. Last time I saw a plug like that, the piston was melted lol.

            When you did a leak down what percent leak were all of them?

            I would get all the injectors flow tested. What kind of gas are u using?

            Low 11s is a bit rich for 10psi with a t28. If you do happen to have a clogged injector then that only means your other cylinders are running way to rich because it's only showing low 11s because of that lean cylinder.

            I kind of want to say is also possibly the tune but it only happened on cylinder #1. Did you dyno tune your car?

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            • #7
              Thanks for the response!

              I had the car tuned at dynospeed in Memphis,TN. The guy who tuned it has many yrs of experience with turning SR20s so I am fairly confident it was a safe tune. I haven't done any logs since I got it tuned but I dug up the old bin file from the tune. I am 90% sure these are the latest maps that are on the car now, will double check that. Not sure what load I am at at 10psi, probably ~100. I do remember him mentioning that he prefers modifying the MAF curve to tune instead of doing alot of work on the actual fuel maps which IIRC is opposite of what Nistune recommends.

              Have a busy week but I am planning to get into it more this weekend.



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              • #8
                That timing map is a bit of a mess...

                I doubt you're at ~13 degrees total timing at only 10 psi on a T28, or if you are... that's not good.
                '18 Chevrolet Volt - Electric fun hatch for DD duty!


                DefSport Koni Sleeve and Spring Perch Buy!!!
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                • #9
                  Would that be 13degrees + base timing??

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                  • #10
                    Stock ecu is total timing with the base timing set to 15 per fsm.
                    '18 Chevrolet Volt - Electric fun hatch for DD duty!


                    DefSport Koni Sleeve and Spring Perch Buy!!!
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                    • #11
                      Pulled the maps from the ecu over the weekend also did a couple pulls on high boost (~15psi) to see what Load Index I was at. Seems like its around 110 at peak torque then tapers down to ~100





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                      • #12
                        Why is the afr so lean well after you've gone WOT? The timing in boost doesn't look bad, assuming base timing is correct.

                        Obviously something is off. How's the blow by on the engine? Oil consumption?
                        '18 Chevrolet Volt - Electric fun hatch for DD duty!


                        DefSport Koni Sleeve and Spring Perch Buy!!!
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