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Old 04-30-2014, 11:36 PM   #1
Gun Jam
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Default how to track down a possible random ignition miss??

my 302 is actually running pretty well but I can't shake the feeling that its got an ignition miss..its been this way for sometime. It seems most likely to occur at smooth steady rpms around 3k but also under wot acceleration

For example it will purr along at 2800 rpm with A/F ratios indicated about 14.3 to 13.5 well in the acceptable range nothing changes and you'll feel a skip in the beat or maybe 2 or 3.

When checking timing curves the timing light (which is Innova brand digital display "dial" back compatible with MSD ignitions) clearly will miss a flash once in a while especially at 3k. I have not tried it on other plug wires (induction pick up) to see if they skip any flashes.

Are induction pickup digital timing lights that are dealing with an MSD system known to skip flashes??...is this really a valid test in this situation?

Is there a better way to check for a missed spark?

The distributor is in good shape and its running off an MSD a6 box which is several years old

Thanks

-Gun
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Old 04-30-2014, 11:42 PM   #2
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What plug wires, how old? How old is the coil? How old are the cap/rotor?
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Old 05-01-2014, 12:36 AM   #3
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Msd 8.5mm not all that old maybe 2 years replaced identical set...I built the set im using now...dont think I screwed anything up.

coil is about 3 years old

cap and rotor are new. changing them didn't seem to make a difference.

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Old 05-01-2014, 03:23 AM   #4
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What plugs? Are they gapped right? You might want to check the plugs for cracked insulators.

How much do you drive it? MSD wires are ok, but if you drive a lot after 2 years they could possibly be an issue.

Could be timing too. Or AFR, or changes in fuel because of seasonal blends.
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Old 05-01-2014, 07:53 AM   #5
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I'll bet dimes to doughnuts that your coil is breaking down.
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Old 05-01-2014, 07:56 AM   #6
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If your distributor has a "ground wire" that runs to the to the coil, you might want to replace it.
This wire flexes every time the distributor is moved. The copper part of the wire can break and become intermittent while the insulation looks OK.
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Old 05-01-2014, 12:02 PM   #7
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they are autolite plugs. I dont remember the gap for certain but I think they maybe .035. they are about a year old

The vehicle is driven most days.

I myself am not a 100% sure its actually losing spark momentarily...I suspect that it is...how can we test this is the real answer Im looking for. There has to be a better solution than looking to see if a timing light skips a beat....any ideas?
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Old 05-01-2014, 03:02 PM   #8
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Dust off the ol' oscilloscope and see what kind of wave it's making..failing that..I dunno.
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Old 05-01-2014, 08:25 PM   #9
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I could always just wait for it to get to the point where its actually a problem then I'll know !!

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Old 05-01-2014, 09:32 PM   #10
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It could be your imagination too.
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Old 05-01-2014, 09:32 PM
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