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missfire ls7 = ( help!!

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Old Sep 30, 2010 | 07:05 PM
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Default missfire ls7 = ( help!!
all of a sudden got a missfire on a 70 chevelle ls7

power to coils ok
grounds ok
new spark wires
new plugs
fuel pressure ok
cam sensor new

anyone ?
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Old Sep 30, 2010 | 09:56 PM
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I was getting misfires on my ls2 from misgapped plugs. I switched to MSD wires which require a larger plug gap and didnt know it. It was causing misfires like crazy.
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Old Oct 1, 2010 | 01:49 AM
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well it just happen out of nowhere,,,allchanges were done after
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Old Oct 1, 2010 | 06:01 AM
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Can you do a "Case Relearn" on the LS7? My LS1 developed a missfire once and I had to do the relearn on it and it fixed it.
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Old Oct 1, 2010 | 09:35 AM
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i dont have that option with my scanner (solus) at least i dont see it
i checked into the injector wiring ,it looks ok,it seems like the ecm may be bad ?
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Old Oct 1, 2010 | 12:55 PM
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check your valvetrain, i have had few ls7's come thru with misfire related to broken valve springs and cracked retainers
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Old Oct 3, 2010 | 09:22 PM
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have someone with tuning software hook it up it might be a tuning issue or case learn needed
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Old Oct 3, 2010 | 09:56 PM
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You need to see what cylinder is causing the misfire and go from there.
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Old Oct 3, 2010 | 10:43 PM
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Have you checked the compression rate if all sylinders are the same? if the compression is all the same and electric everything is in order you may have a valve train proplem, so you may need to got the sylinders head out.
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Old Oct 3, 2010 | 11:12 PM
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i will check up on that next
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Old Oct 3, 2010 | 11:19 PM
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oh by the way ,its cylinder # 3 and the plug looks brand new still ,i pulled the fuel rail and injector sprays ,when i tested the injector signal with the snap on vantage it wouldnt get a signal,car isnt mine ,its my friend`s car ,it wass tuned by synergy ,it has an aftermarket cam too so i have no real detail on what was done other than the car was running ok and all of a sudden it started missfiring driving @ 10-20mph ...that night i didnt have my compression gauge tester so i was unable to check for compression even thought it didnt have a sound that was weird
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Old Oct 3, 2010 | 11:25 PM
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Do a leak down test also.
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Old Oct 3, 2010 | 11:29 PM
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yeah i will be doing that too,thanks
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