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When the car was idling in the garage this morning (hooked up to HP Tuners), I saw a spike on the "Spark" graph at the same time as the car stumbled. "Control Module Voltage" also went from > 14 down to 13.69. Not a massive difference, but I don't know what the operating range for the computer is, so I can't tell if that's a real problem. It's weird that voltage would drop, though.

RPM also dropped from 850 down to about 740, then came back up.

Here's the chart:enter image description here

It did this twice more over the course of about 10 minutes.

Pᴀᴜʟsᴛᴇʀ2
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3Dave
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3 Answers3

2

That is a lot of spark advance. It looks like its sitting at 5-7ish degrees, then pulls up to almost 30 suddenly. Thats way higher than any normal adjustment I've seen.

his data with a line added I added my own line onto your graph, and it looks like the voltage drop coincides with the start of the spark advance. Based on this, the fact that the MAP is suddenly blown, and the stalking I did on some of your previous questions where you mention sticky valves... It sounds like it could be a misfire that went back into the intake instead of out the exhuast. That could/would blow your MAP and maybe set off the knock sensor (which would violently pull timing, as we see here).

But those are pretty rare from my understanding. Maybe it was just a Gremlin.

Community
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Zshoulders
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To get this off the unanswered question list:

There was an intermittent break in the wiring harness near the MAP sensor. I removed the damaged section and lineman-spliced it, and this particular problem disappeared.

3Dave
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Doesn't this car have two MAP sensors? See this discussion forum for more information. Seems like one of them involves temperature, so you may have replace them as a pair.

Carguy
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