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Thread: number 5 and 6 cylinder missfire??

  1. #11
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    check the spark plug for cracks, hell even replace it 15,000 miles is a short period but I have seen ones bad, I have had to replace them at 10,000 on my truck when I had the supercharger on. If not, it must be mechanical, sticking valve, or the start of a head gasket failure.
    2005 chevy silverado, duramax tuned with efilive
    1997 Saturn sc2 turbo, tuned with megasquirt on e85
    2000 s-10 turbo'd tuned with efilive on e85

  2. #12
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by joecar View Post
    You said your compression test was 135-150 psi spread, which cyl# was the 135 on...?

    Also, you can use the DVT controls to shut of any one injector... do this:
    - set engine running with some load (e.g. in gear, some throttle, assistant has his/her foot on brake to hold vehicle stopped).
    - start logging,
    - goto DVT tab, select your PCM,
    - on DVT tab, goto Engine Control subtab,
    - on Injector Control, click on #1, wait a 3 seconds (count out loud), click on Enable All, ,wait 3 seconds...
    - repeat this for all 8 cyls.

    When done, look at your log, you should see 8 significant dips in RPM (each 3 seconds in length)...

    if a cyl was misfiring then its RPM would not have dropped.

    Be Safe when doing this.
    I would assume the the number 6 is the correct missfire. I also have a po306 code along with the number 6missfire on the scan. Not really sure what this is supposed to accomplish? Are you saying that maybe this is a false missfire?
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  3. #13
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by chevy052500hd View Post
    check the spark plug for cracks, hell even replace it 15,000 miles is a short period but I have seen ones bad, I have had to replace them at 10,000 on my truck when I had the supercharger on. If not, it must be mechanical, sticking valve, or the start of a head gasket failure.
    swaped the number 6 plug for the number 4 plug still number 6 missfire. If it were a start of a head gasket why would it still have compression and also hold compression??
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  4. #14
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by chevy052500hd View Post
    check the spark plug for cracks, hell even replace it 15,000 miles is a short period but I have seen ones bad, I have had to replace them at 10,000 on my truck when I had the supercharger on. If not, it must be mechanical, sticking valve, or the start of a head gasket failure.
    actually now that you mention it number 6 was a little low on the compression test. it was 125 and number 2 was also lower than the rest at 130
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  5. #15
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    It may be possible that the head gasket is breaking down slowly, they did this on my duramax, I started noticing the coolant system was still pressurized when it was stone cold, then slowly started feeling a miss, and now it is eating coolant. It's not a complete failure yet just slowly starting .... been seeing this more on cars with aluminum heads and iron blocks in high mileage situations. Any condensation under the oil cap?
    2005 chevy silverado, duramax tuned with efilive
    1997 Saturn sc2 turbo, tuned with megasquirt on e85
    2000 s-10 turbo'd tuned with efilive on e85

  6. #16
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by chevy052500hd View Post
    It may be possible that the head gasket is breaking down slowly, they did this on my duramax, I started noticing the coolant system was still pressurized when it was stone cold, then slowly started feeling a miss, and now it is eating coolant. It's not a complete failure yet just slowly starting .... been seeing this more on cars with aluminum heads and iron blocks in high mileage situations. Any condensation under the oil cap?
    none and it doesn't use any coolent either.
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  7. #17
    Joe (Moderator) joecar's Avatar
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    Get a block test kit from part store, $50, it tests for presence of combustion gases in coolant.

  8. #18
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by joecar View Post
    Get a block test kit from part store, $50, it tests for presence of combustion gases in coolant.
    If it were a "burnt" valve it wouldn't hold compression in that cylinder. In this case it does hold. And if it were leaking combustion gases in the coolent it would be evaporating the coolant or boiling it. and it doesn't do that either.
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  9. #19
    Joe (Moderator) joecar's Avatar
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    Did you also do a leakdown test which is a bit different than a compression test...?

  10. #20
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by smslyguy View Post
    If it were a "burnt" valve it wouldn't hold compression in that cylinder. In this case it does hold. And if it were leaking combustion gases in the coolent it would be evaporating the coolant or boiling it. and it doesn't do that either.
    Yes, the later part of the thread steered toward ignition components...

    it might even be your PCM... but first you have to eliminate all possibilites... you need 2nd and 3rd "opinions" from different test tools... i.e. compression test, leakdown test, block test kit should all agree with each other.

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