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Old 06-17-2017, 09:46 PM   #1
Xeroni
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Default MS1 noise in CLT and IAT when in boost

I noticed this starting to happen when I was on the way home from Davis this year. Didn't have the laptop hooked up to datalog so this is the first time I've recorded it since I had to swap the trans. Whenever I start to build boost the coolant and iat sensor readings osculate like crazy and cause the fueling to lean out. The ms tries to fix this by putting more fuel but it just maxes out the ego correction and if I have autotune on it maxes the cells out at 255.

I have an old log where it spiked up to 400* At first I suspected a ground issue. I redid them so they all ground to the head and from there it goes back to the firewall. Didn't do anything. I noticed that the voltage reading is lower than what the battery says, about a whole volt lower on ms.

Needs more grounds? Should I adjust the voltage correction settings in ms itself?
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Old 06-17-2017, 09:50 PM   #2
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What do you have for block to chassis grounds?
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Old 06-17-2017, 09:53 PM   #3
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The stock ground from the accessory bracket to the battery is the only one I know of.
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Old 06-17-2017, 10:27 PM   #4
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A sufficient block to chassis ground would be a good start.
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Old 06-18-2017, 01:27 AM   #5
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Well the ground wire at the bracket was loose. I've tightened that up, the battery voltage reads closer to what it should be. I was going through my settings and I noticed that the squirts per cycle was at 1. I remember that being at 2 when I was tuning the car, don't know if I accidentally changed it or what. I don't know if that would make a difference but my injector dead time settings aren't perfectly right so it might? I'll try it out tomorrow.
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Old 06-18-2017, 12:58 PM   #6
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Coolant temperature readings will not affect the fuel equation once you are off WUE and ASE unless you are using the coolant based IAT compensation in MSExtra. IAT errors will affect fueling with high IAT readings resulting in shorter pulse widths. The IAT measurements should not be directly affected by ground loop currents if you brought an isolated IAT ground back to the ground terminals on the MS1 box. Grounding the IAT at the measurement device or any point on the engine block or any place other than at the MS DB connector is bad practise. If your IAT is a single terminal RTD replace it with a two terminal RTD and run the two wires back to the MS DB connector. Using twisted pair is nice; but, should not be necessary if you stay away from the ignition wiring. All sensors attached to the MS should have isolated grounds connected back to the MS to avoid measurement errors caused by ground loop currents.



A bad connection between the MS box and ground can be a problem. If the injector drivers are in the MS box the bad ground connection can result in lower voltage applied to the injectors. Lower operating voltage increases injector offset (opening time). If injector offset voltage sensitivity is not correctly configured in MS the reduced injector voltages could result in lower than expected pulse width duration.
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Old 06-19-2017, 12:14 AM   #7
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The IAT spikes are now only 1 degree up/down which seems to be fine. CLT still jumps from around 194 to 210 though.

IAT is grounded to body up front, CLT is the head. All in all it seems more stable.

I've attached a log of today's run. Above 150kpa still needs work, I'll work on that before I try again.
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