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Old 10-16-2012, 02:07 PM   #1
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Default Misfire during idle at at light throttle

Hi everyone, so I've been experiencing a miss at idle at very light throttle for quite a while now. I took the car the bell engineering and did a compression test and leakdown and my 4th cylinder was missing for some reason. We determined it was the rings in said cylinder so I ended up building my bottom end but I still have the same miss. Performed another compression test and my results were: 140, 140, 148, 140. With three cranks for each cylinder using a crappy gauge. Just tried switching the cam and crank sensors which didn't make any change. Thoughts are it wouldn't be the coil because I would have 2 cylinders missing. I've changed the order of my injectors and spark plugs and miss is still in the same cylinder. Help!
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Old 10-16-2012, 02:38 PM   #2
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log the events.
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Old 10-21-2012, 12:15 PM   #3
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I'm just curious, how do you know it's cylinder 4? Does Megasquirt have a misfire counter? I haven't quite gotten that far in my megasquirt research.
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Old 10-21-2012, 12:57 PM   #4
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Serial cord is at my parent's house a couple hours away so i'll get that soon. And when I take off the plug wire off the 4th cylinder, the car runs the same.
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Old 10-25-2012, 11:36 AM   #5
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...
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Misfire during idle at at light throttle-coilpack_test.jpg  

Last edited by cowboys647; 10-25-2012 at 11:56 AM. Reason: I'm an idiot
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Old 10-26-2012, 05:31 PM   #6
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I had a problem similar to this I would get a mid at throttle tip in, ended up being a bad connection between the spark plug wire and coil tower.
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Old 11-16-2012, 04:31 PM   #7
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Plug wires to the tower are all clean and connected well. Here's a log of the miss at idle.
Attached Files
File Type: msl miss idle.msl (225.4 KB, 76 views)
File Type: msq CurrentTune.msq (78.9 KB, 74 views)
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Old 11-16-2012, 06:26 PM   #8
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check your grounds
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Old 11-16-2012, 06:48 PM   #9
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Quote:
Originally Posted by Clos561 View Post
check your grounds
I checked and cleaned the grounds and then rechecked and re-cleaned them. I can't see it being a ground..
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Old 11-18-2012, 01:01 PM   #10
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Bump. Anyone?
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Old 11-21-2012, 01:57 PM   #11
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Maybe something came loose in my ecu? I'm pretty much out of ideas here
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Old 04-09-2013, 06:33 PM   #12
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So I have an update on my issue. I've got the car driving again and got to do some logs and try to tune some. From looking at the logs, it seems my battery voltage is erratic in the same way that my afr is. Here is a couple screenshots and the log. What would make my voltage all erratic like that?
Attached Thumbnails
Misfire during idle at at light throttle-voltage-idle-miss.jpg   Misfire during idle at at light throttle-voltage-causing-miss.jpg  
Attached Files
File Type: msq CurrentTune.msq (89.0 KB, 57 views)
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Old 04-09-2013, 06:34 PM   #13
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Different log taken today because for some reason I can't load the other one..

Edit: Also I had trouble when I first installed my ms with my nb alternator so I swapped in an internally regulated na alternator and wired it accordingly. Not sure if maybe that has something to do with it
Attached Files
File Type: msl Showing miss at idle and light throttle.msl (1.20 MB, 66 views)

Last edited by cowboys647; 04-09-2013 at 06:55 PM.
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Old 11-18-2013, 12:12 PM   #14
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Did you ever come to a conclusion to this? I'm having a similar problem with light load misfire and my tach, water temp, and oil pressure gauges go crazy under load over 50mph. I was told it was a grounding issue but I'm still trying to figure it out.
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Old 11-24-2013, 11:38 PM   #15
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Quote:
Originally Posted by cowboys647 View Post
Hi everyone, so I've been experiencing a miss at idle at very light throttle for quite a while now.
My MSM does that too -- only when the engine is ice cold. If I let it warm up properly and then drive, it's fine. If I turn it on, pull out of the driveway, and just start going (even staying in vacuum), then sometimes I get a misfire CEL.
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