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Old 01-26-2009, 08:30 PM   #1
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Default RPM dropping intermittently during warmup

I am having an issue with the rpm signal that is intermittent, but seems more frequent lately. The problem is either there or it is not during the extent of my drive, but significantly worse during warmup when it is. Looking at logs, it is being caused by major rpm drops that make it feel like fuel cut launch control (because it is cutting fuel), except much more harsh. The symptoms seem to suddenly turn on after a certain degree of throttle position or engine load is present.

Today when I got in my car to go home from work, I had to drive between 1000 and 2000 rpm at first because after 2k it would completely cut out fuel and fall on its face. By the end of the drive, I was able to rev it a little over 4k, but only with light throttle. At any time, I could have induced the stumble by pressing the gas moderately hard, regardless of RPM.

Help me to figure out why this is happening, my msq and a datalog are attatched.
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RPM dropping intermittently during warmup-graph.jpg  
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File Type: msq Ryan 230cc NA.msq (35.2 KB, 62 views)
File Type: xls datalog_stumble.xls (55.5 KB, 45 views)
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Old 01-26-2009, 08:46 PM   #2
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Dying CAS is my guess. That or the wiring to the CAS is suspect.
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Old 01-26-2009, 08:54 PM   #3
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Quote:
Originally Posted by patsmx5 View Post
Dying CAS is my guess. That or the wiring to the CAS is suspect.
Cas was my thought too, ill have to take a look at the wiring, maybe the plug is loose
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Old 01-26-2009, 09:15 PM   #4
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although, if it was the CAS, why does it seem to turn on and off depending on the load? A dying CAS would be a constant issue right?
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Old 01-26-2009, 09:49 PM   #5
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what firmware? .1uF mod?
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Old 01-26-2009, 10:11 PM   #6
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yes, cap mod is present and I am using 270 ohm resistors for ign pullup.
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Old 01-26-2009, 10:24 PM   #7
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you losing the CAS signal, so it's either the CAS or the wiring.
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Old 01-26-2009, 10:36 PM   #8
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thanks scott, ill have to take a look at the wiring later.
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Old 02-07-2009, 05:12 PM   #9
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Well i didn't have any problems for a few weeks, but this morning the car wouldnt start and i decided to look at the megasquirt. There was some condensation on the case, and I wouldnt be surprised if there was a bit inside as well. Took the board out, cleaned it with some alcohol and a toothbrush, blow dried it and now it's working fine. I think the problems correlate with periods when it has been raining.

Crossing my fingers
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Old 02-07-2009, 05:51 PM   #10
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my old miata used to leak hardcore at the passenger footwell, I'm surprised it never shorted the ECU.
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