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78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
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---
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title: Missing Tooth
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description: Information about the missing tooth decoder pattern
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published: true
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date: 2020-01-06T00:30:19.884Z
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tags:
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---
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# Missing Tooth Pattern
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## Overview
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A missing tooth crank trigger is used as standard equipment by a number
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of OEMs, most notably Ford, but is also very popular as an aftermarket
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fitment.
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It is comprised of crank wheel with a given number of evenly spaced
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teeth, and one or more 'missing' teeth. Common values are typically
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60-2, 36-1, 24-1, 12-1 and 4-1 where the first number represents the
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total number of teeth the wheel would have if there were none missing.
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The second number after a dash "-" indicates the number of teeth
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missing.
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*Note: If there is a third number (e.g., 36-1-1), the missing teeth are
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not sequential, and this decoder does not apply. Do not confuse counts
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with slashes "/", as numbers following slashes represent cam teeth—not
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missing teeth. Wheels with "+" indicate added teeth rather than missing,
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and again this decoder does not apply.*
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## Applications
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Missing tooth crank wheels can be used on virtually any engine and is
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one of the more popular aftermarket options. It provides very good
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resolution in the higher tooth count versions (Eg 36-1 and 60-2) without
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being CPU intensive to decode.
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## Tuner Studio Configuration
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<center>
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<img src="https://raw.githubusercontent.com/speeduino/wiki/master/decoders/missingtooth_triggerconfig.png" />
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</center>
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Fields:
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- Primary base teeth: This is the number of teeth the wheel would have
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if there were none missing. Eg a 36-1 wheel has only 35 actual
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teeth, but you would enter 36 into this field.
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- Missing Teeth: The size of the 'gap' in the number of teeth. These
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missing teeth must be situated in a single block (ie there's only a
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single gap in the teeth
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- Trigger Angle: This is the angle in crank degrees **AFTER** TDC
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(ATDC) of the first tooth following the gap
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### Timing Setting
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The trigger angle can be found by placing the engine at TDC, then
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calculating how far it must be rotated until the first tooth after the
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gap reaches the sensor.
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### Sequential operation
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The missing tooth decoder supports sequential operation if an additional
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cam input is present. If Sequential mode is selected for either the fuel
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timing or spark timing, the system will expect to see a cam signal and
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will not sync correctly without this. Note that this is ONLY the case if
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sequential is selected for one or both of fuel and spark timing.
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This cam signal should take the form of a single pulse every complete
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cycle. This can be a short tooth or a half moon type arrangement,
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provided that electrically there is only a single rising (or falling)
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pulse per cycle.
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## Trigger Pattern
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<img src="https://raw.githubusercontent.com/speeduino/wiki/master/decoders/missingtooth_trace1.png" width="100%" />
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