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Old 05-29-2007, 06:07 PM   #1
Ben
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Default intermittent miss

Got a miss going on. It's intermittent. When the miss occurs, my wb reads full lean. I'd normally think secondary ignition, however when this miss occurs, the tach will drop ~500 rpm for an instant concurrently with the miss. It typically occurs while cruising between indicated 3k-3.4k rpm (but that may be because that's where I cruise at around town). But once I noticed it happening while decelerating in gear with my foot off the gas.

What would cause an ignition miss AND a simultaneous drop in RPM reading on the tach? CAS related? I do have a butt connection where the MSD box used to intercept the signal.

I have extra plugs & wires. Could throw them in to see what happens, but I'm not betting on secondary ignition because of the tach phenomenon.
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Old 05-29-2007, 06:47 PM   #2
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Quote:
Originally Posted by Ben View Post
Got a miss going on. It's intermittent. When the miss occurs, my wb reads full lean. I'd normally think secondary ignition, however when this miss occurs, the tach will drop ~500 rpm for an instant concurrently with the miss. It typically occurs while cruising between indicated 3k-3.4k rpm (but that may be because that's where I cruise at around town). But once I noticed it happening while decelerating in gear with my foot off the gas.

What would cause an ignition miss AND a simultaneous drop in RPM reading on the tach? CAS related? I do have a butt connection where the MSD box used to intercept the signal.

I have extra plugs & wires. Could throw them in to see what happens, but I'm not betting on secondary ignition because of the tach phenomenon.
Can you see anything on a datalog? If the CAS is dropping out due to those two butt connectors in there giving out then we might be able to see it there...

Is it rare, or somewhat consistent?
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Old 05-29-2007, 07:05 PM   #3
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It started as occasional, but seems to be getting more frequent. I see these little spikes of 0 injector activity in my datalog. I assume it's related.

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Old 05-29-2007, 07:12 PM   #4
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My money is on bad earths
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Old 05-29-2007, 07:35 PM   #5
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It's the factory harness so that normally shouldn't be a problem... though I think the grounds were vampire tapped for the wideband which can damage them.

Ben-- email me your full datalogs so I can take a closer look.
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Old 05-29-2007, 07:53 PM   #6
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I second that, either a poor ground or poor power
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Old 05-29-2007, 08:01 PM   #7
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datalog for anyone else interested.
Attached Files
File Type: zip mondaymay28tuningsession.zip (571.6 KB, 43 views)
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Old 06-03-2007, 12:46 AM   #8
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problem seems to be cured by swapping in a different ignitor.
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Old 06-03-2007, 01:13 AM   #9
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i had my money on ignitor as well it sends out RPM signal maybe your dwell time is cooking it slowly and then it starts to miss. just a theory
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Old 06-03-2007, 03:19 PM   #10
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Quote:
Originally Posted by Ben View Post
problem seems to be cured by swapping in a different ignitor.
Thinking about it I have the same issue, and I assumed it was bad leads (a different set solved it for a time).

Think I'll try swopping the coils for a spare set I have and see what happens.
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