Electrical or tune related?

94tang

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Aug 24, 2003
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I've had my microsquirt for over a year now on the car (94 mustang). For the most part, i think the tune is pretty good (except idle but thats another topic). for the past several months Ive been having an issue i cant figure out. The rpms will drop to zero briefly, like for a split second. It doesnt show up on the data log, but i can see it on the factory tach. It only happens under part throttle cruise and usually when the car is warmed up. would someone please look over my tune and see if im missing/forgot something?

thanks
 

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94tang

Member
Aug 24, 2003
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well this is the current tune ......i couldnt get todays data log to upload, cause for some reason its showing it as an .mlg file instead .msl like all the rest
 

a91what

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Mod Dude
Apr 6, 2011
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The datalog and tune file are either not from the same car or some kind of ign table changes have been made. I can see in the datalog the ign values are different. I see no issue with the RPM signal into the MS from the log file. IF the car does not feel like it is dying when this event happens, then i would suspect something in the tach circuit... does the ecu feed the tach in your installation?
 

94tang

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Aug 24, 2003
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Idk Steve...its a plug n play if that helps

when the "incident" happens , the car stutters for just a split second


I did make some ign changes earlier and after the data log
 

94tang

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Aug 24, 2003
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As i stated earlier, the drop in rpms doesnt show on the data log for whatever reason. But i personaly witnessed the tach drop dramatically....maybe down to 200 or 300 rpms
 

a91what

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Mod Dude
Apr 6, 2011
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It appears the tach is fed from the negative side of the coil just like on a fox. Can you feel the RPM drop in the engine or is it just a phenomena with the tach? If its just the tach then i would assume that the issue is either the tach itself or the wiring
 

94tang

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Yes, the car "stutters" for a split second. I think in the data log you see the iac valve pulse suddenly to a higher value
 

a91what

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Mod Dude
Apr 6, 2011
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I am seeing normal behavior from the idle valve based on the provided tune. The pip signal looks clean on the input side and i do not see any sync loss errors in the log file.
What i do see are lean spots in the tune as you transition into new gears and come off idle, that will make the car stutter. I do not see anything rpm related on the datalog that coincides with the RPM signal dropping out however
 

94tang

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Aug 24, 2003
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I guess the search continues.....thanks for help Steve


Fwiw i installed a new pickup in the dizzy hoping this was the problem but apparently not
 

94tang

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What i still find odd, is the rpm drop not picking up in the data log. It clearly and absolutely happens. Maybe its happening too fast....?
 

a91what

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Mod Dude
Apr 6, 2011
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Hillsborough county
nope, the ecu is seeing the pip signal from the distributor.... you are experiencing missfires from what i gather. I would check the TFI and the coil along with all associated wiring
 
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94tang

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Aug 24, 2003
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East TN
FWIW, i found the issue. I have an inverter in the car to keep my laptop charged. Its a 400/800 watt model wired directly to the battery with a 50a fuse. When i have the inverter on while the laptop is on/hooked up to the microsquirt, thats when i have the aforementioned issues. With the inverter off/not charging=no issues......go figure
 
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