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Lift if your car misfires

Posted by kiggly, Nov 28, 2015

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  1. kiggly

    kiggly Supporting Vendor

    278
    113
    Joined Feb 17, 2003
    Ann Arbor, Michigan
    I've been a bit sparse on the forums lately for adding in tech data, although the last year has produced gobs of information. Over the next month I'm planning to post up a pile of combustion-related data. This past year has been pretty exciting for us from a technical point of view. The drag car has been on methanol since the start of the season. Many little lessons have been learned there, but the main one is the fuel change wasn't a magic bullet for the car's knock issues. Pending some testing for final confirmation with a header change, that is now root-caused as reversion and chamber residuals. The last dyno session with some smaller cams showed slightly less knock on the cylinder pressure metrics, but the plugs now started coming out without any speckles at all. Previously they always were peppered up.

    During the last session at Force Engineering on Halloween morning, we were able to get it sorted to 817whp on their mustang dyno. We did run into a couple hiccups with the tune on the smaller cams. I was running it open loop initially, but noticed the midrange was way leaner than desired, to the tune of 20% off target. The AFR was just on target up top, at about 0.62La. I enabled the closed loop in the Haltech Elite for the full range and immediately figured out just how much of a screwed up step was in the map. It added in about 18% fuel and immediately afterward pegged the wideband rich at 0.55La. Going through the fuel used, I think it was in the high 0.4x La range. The 0.2sec swing from dead-on AFR to dead-rich was too fast for my settings on the control loop and really just the fault of a crappy map. The car immediately broke up rich. I didn't think much of it until processing the combustion data.

    When processing the data, I found that it flashed over combustion to the intake manifold and slowly burned into the chambers. Combustion in the manifold is dead slow compared to in the chamber. It burns so slowly at the 9k range that it will take multiple engine revolutions to finish burning all the air and fuel in the intake. When this happened, it also breathed clean air into chamber #4, but then began burning before the intake valves closed. Immediately at valve closing the cylinder pressure began to rise quickly. Normal combustion pressures were in the low 3000psi range and this single cycle was up in the 5500psi range! This nearly doubles the stress on all the parts and it was all just caused by a misfire. There was no audible backfire or anything, this sounded like a normal break-up. The parts all look good, FFWD's Cylon rods and Wiseco 1400HD's lived through this and don't appear to be damaged upon teardown and inspection.

    Here is the golden nugget, there are 3 normal combustion cycles, one with relatively intense knock. There is the single flashover and preignition cycle, and there is the cycle after the flashover where it has elevated intake manifold pressure due to the backfire and no combustion because the fuel and oxygen was already spent during the backfire.

    So, lift if it misfires or this might happen - particularly on methanol:
    8650rpm_Intake_Pressure_20151031_pull6 - flashover.png

    This also explains why cars sometimes blow rods through the block if you stay in it during misfires. I've seen others have that happen a couple or three times.

    Thanks,
    Kevin
     

    Drag Race Build 4K  7

    1991 Plymouth Laser RS Turbo
    7.687 @ 182 · 1G DSM
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  2. motomattx

    motomattx Proven Member

    2,135
    789
    Joined Dec 9, 2010
    wampum, Pennsylvania
    Very nice to see it in a graph, I knew of this phenomenon but imagined it rather than seeing the raw data, thanks for posting.
     

    Drag Race Build 3K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  3. rhamlinii

    rhamlinii Proven Member

    596
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    Joined Nov 8, 2003
    Baltimore City, Maryland
    Nice information.
     

    4K  0

    1992 Eagle Talon TSi AWD
    manual · 1G DSM
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  4. redrkt

    redrkt Proven Member

    96
    10
    Joined Apr 21, 2003
    kalamazoo, Michigan
    That is some insane instrumentation you have setup on your car. What caused the flashover of combustion into the intake manifold, and would/should you see temps in the intake manifold spike when this happens? Are you injecting methanol into the intake manifold-I/C piping as well?
     

    421  0

    1992 Mitsubishi Eclipse GSX
    11.988 @ 115.020 · 1G DSM
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  5. DSMReviver

    DSMReviver Proven Member

    816
    74
    Joined Mar 4, 2008
    Little Rock, Arkansas
    Kevin thanks for posting. I had a miss fire on WOT a couple of day ago and now i am worried. I hope i didn't damage anything. Ecmlink is estimating 490whp when that happened :(
     
    DSMReviver

    1K  0

    1995 Mitsubishi Eclipse GSX
    manual · 2G DSM

    Showcar Build 935  0

    1998 Eagle Talon TSi AWD
    manual · 2G DSM
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  6. kiggly

    kiggly Supporting Vendor

    278
    113
    Joined Feb 17, 2003
    Ann Arbor, Michigan
    I was only injecting fuel into the ports on this dyno pull. That includes one injector in the OEM location and another at the top of each runner, pointed down it very similar to V8/V10 era F1 cars. I am also injecting fuel in the upper IC pipe now too.

    Update on that misfire event - it did bend the wristpin slightly, seeing about 0.005" runout at the middle. That is not much of a surprise as the pressure for that cycle was ugly-land out of normal.
     

    Drag Race Build 4K  7

    1991 Plymouth Laser RS Turbo
    7.687 @ 182 · 1G DSM
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    mercaholik likes this.
  7. bastarddsm

    bastarddsm Proven Member

    4,473
    1,024
    Joined Aug 26, 2003
    Mendota, Illinois
    Kevin what do you use for pins?
     

    Showcar Build 5K  1

    1991 Eagle Talon N/T
    9.805 @ 144.00 · 1G DSM
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  8. kiggly

    kiggly Supporting Vendor

    278
    113
    Joined Feb 17, 2003
    Ann Arbor, Michigan
    These are the off the shelf 22mm X 0.225" wall pins from wiseco in their 1400hd pistons. The newer hd2 stuff with the shorter pins should be a little bit more tolerant. This was a very ugly event though, definitely buckled steel rod or blown mls head gasket territory. Force on the piston was in the 50,000lb range.
     

    Drag Race Build 4K  7

    1991 Plymouth Laser RS Turbo
    7.687 @ 182 · 1G DSM
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