High Rpm Engine Miss

Discussion in 'Fox 5.0 Mustang Tech' started by brian69, Aug 29, 2013.

  1. brian69

    brian69 New Member

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    I have a 93 with a 306 8.6-1 comp, tfs heads and intake, Anderson b31 cam, c4 3500 conv, 373 rear ,vortech si 17 psi, 92 mm pro m, 60lb injectors, aeromotive fuel pump glens rails -10 feed line -6 return, snow meth injection, Anderson pms series 4 with map, msd ignition, dist, 6al and coil.
    My problem is at around 6000 rpm its starts to misfire BAD!!!! I have changed MSD box, dist, plugs and wires.
    My afr is at 11-1 when this happens, I've added a little fuel and removed some fuel with no change. Also added a little timing and removed some as well with no change. I removed the supercharger belt and has no change without boost. Tried a different brand of fuel (93 octane with lucas octane booster) Engine temp seems to have no affect on it. Plugs are Autolite 3923 gapped at .028", Base timing set at 10 degrees.
    I'm drawing a blank....Any help would be GREATLY appreciated!!!!!
    Thanks Brian.
     
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  2. mikestang63

    mikestang63 Mustang Master

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    Valve springs & pressure?
     
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  3. brian69

    brian69 New Member

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    Heads set up by machine shop to cam specs. I actually thought about this but I figured it would have gradually started, This just came on out of nowhere. Last week I tried a few things and thought I had it fixed, I had the rev limiter set to 6900 and my tack showed peak at 6870 so I think that would rule out float, It pulled hard several times then it came back !!!!!!!!!!!!
     
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  4. madspeed

    madspeed Colonel Mustard
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    pull codes? koeo and koer
     
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  5. brian69

    brian69 New Member

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    No codes
     
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  6. madspeed

    madspeed Colonel Mustard
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    does it make any change if you turn off the meth?
     
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  7. madspeed

    madspeed Colonel Mustard
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    did cylinder balancs test during koer testing?
     
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  8. brian69

    brian69 New Member

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    No Meth when the blower belt was off and was still doing it. Forgot to mention compression test is good so is leakdown
     
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  9. 88LX5.Oh

    88LX5.Oh Advanced Member

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    You should be getting at least one code, and that should be 11. If you are getting no codes at all, you might have a wiring or a computer problem. Code 11 is system pass code, that means the computer passed it's self diagnostic test. I think. Lol
     
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  10. brian69

    brian69 New Member

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    Yes it has codes but they are for the removed emissions equipment. It has no codes that are related to anything else
     
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  11. madspeed

    madspeed Colonel Mustard
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    and those codes are?
     
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  12. 84Ttop

    84Ttop They make new pistons every day, so why worry?
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    Had a car on the dyno last night with similar problems. We found the issue to be in the PMS wiring harness. Jiggle the harness car runs flawlessly, Jiggle it again and the pops, misses and drops cylinders in the upper rpm range. Changed the harness....no more problems. It seems like recently Andersons quality has really decreased. Years past, you would hardly ever see a problem with their stuff. Recently have seen problems with some of the new PMS'.
     
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  13. madspeed

    madspeed Colonel Mustard
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    mine use to have a high rpm miss, Through looking at my datalogs i narrowed it down to maf voltage. Did a little digging and it ended up being a bad wire at the maf connector
     
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  14. madspeed

    madspeed Colonel Mustard
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    are you able to datalog?
     
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  15. 84Ttop

    84Ttop They make new pistons every day, so why worry?
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    This would provide more valuable information than anything else!!!
     
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  16. brian69

    brian69 New Member

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    Can't datalog
     
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  17. brian69

    brian69 New Member

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    Had a problem last year with it going lean at part throttle ended up being a bad Abaco maf replaced it with a pro m 92. But we have seen newer parts bad. You guys have given me some good things to check into thanks!!!
     
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  18. brian69

    brian69 New Member

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    UPDATE: I bypassed my 2nd new (less than a week old) MSD 6Al and it pulls clean to 6900 rpm! I'm thinking it's that cheesy jumper harness that MSD sells that is my problem. Just ordered another one will see in a few days. Any of you guys seen this before? I can't check connection in one end of the harness as it is molded.
     
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  19. madspeed

    madspeed Colonel Mustard
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    I'm very new when it comes to tuning, but just looking at some of my datalogs has helped me at least understand some of what the computer is seeing/doing and identify at least my one prolem
     
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  20. mikestang63

    mikestang63 Mustang Master

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    I swear I had this typed last night around midnight but forgot to post... Chalk up another problem related to a My Spark Died product.

    Now it's late so I'm trying my best educated guess.. I'd be looking at your MSD ignition somewhere- box, distributor. If you bypass the 6al and just use the coil I wonder if that fixes it..
     
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