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Practical Standalone Tuning: Arming Threshold

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Arming Threshold


00:00 Arming a threshold is a setting in the ECU that is specific to reluctor sensors.
00:05 It's important to understand what it does and how it works as occasionally we may need to adjust this table.
00:12 A reluctor pickup inherently has quite a lot of background noise, but that doesn't present a big problem because the background noise is quite low relative to the size of the signal.
00:22 Both the signal amplitude and that of the noise will increase with engine RPM though so the ECU needs a way of ignoring the noise and only concentrating on the signal.
00:31 This is done with the arming threshold table which is a 2D table of arming voltage versus RPM.
00:38 Basically, the ECU waits until it sees the voltage on the trigger input rise above the arming threshold.
00:44 At this point the trigger input is armed and ready.
00:47 When the voltage drops back through zero volts this is the point where the ECU triggers.
00:53 Now if the arming threshold is set too high, the trigger input may never reach it hence the ECU will ignore all trigger inputs.
01:01 This is especially an issue at low RPM when the trigger amplitude might be quite low.
01:06 On the other hand, if the arming threshold is set too low, background noise may be enough to make the ECU arm resulting in an erratic RPM signal.
01:15 The rule is to set the arming threshold at 1/3 of the peak signal voltage at each RPM point in the arming table.
01:23 This is pretty difficult without the aid of an oscilloscope so you can actually measure the signal though.
01:28 Generally, the default arming threshold will be fine for most stock engines, but occasionally you may need to adjust the table.
01:35 Without a scope you're not going to know if the table needs to be increased or decreased.
01:39 So you're going to need to try both options, and see which works to remove your triggering issue.
01:45 Generally, if the arming threshold is too low, the ECU will receive too many trigger events, and this produces an erratic RPM trace.
01:54 You can often see this in datalogs where the RPM is reaching unrealistic peaks of say 20,000 RPM in an instant.
02:01 If the arming threshold is too high, the ECU won't see any RPM at all.
02:06 The tip here is to start with an arming threshold of around 0.3 to 0.5 volts at 0 RPM, and increase this smoothly to around 4 volts at 7,000 RPM.