VR Conditioners

Getting the best crank and cam signals for your installation

Why do VR sensors need conditioning?

Output is not a clean square wave Signal intensity gets higher as RPM

increases There is no one size fits all VR conditioner

Why isn't there a one size fits all? An aftermarket EMS has to work with a

wide variety of VR sensors Different minimum and maximum peak

voltages Different signal to noise ratios Different wheel patterns

Virtually any aftermarket EMS may need some help when dealing with a sensor that is a bit away from “average”

Diagnostic / High Speed Loggers

Available in MS3, MS2/Extra, MS1/Extra (no composite logger in MS1/Extra)

Tooth logger displays time between crankshaft teeth

Composite logger displays oscilloscope-like graph of crank and cam signals

Trigger logger is post wheel decoder

Tooth logger

Height of bars represents time between teeth

Works best for wheel patterns where there are equally spaced base teeth with gaps 1-3 teeth long

Suggested for generic wheel decoder with missing teeth, 36-2-2-2, 36-2+2, 420A, Rennix, Rover, and similar patterns

Sample tooth log

60-2 wheel while cranking

Composite logger

Displays crank and cam signals Best for spark modes that rely on cam

sensor, or wheels with large gaps between teeth

Preferred for dual wheel without missing teeth, Subaru 6/7, 4G63, '99-'05 Miata, GM 7X, and others

Composite logger rows

Top (green) row – cam sensor Middle (blue) row – crank sensor Lower (red) row – sync flag Pulses where the decoder lost sync are

flagged by vertical lines on lower row

Sample composite log

36-1 wheel with cam shown

Trigger log

Shows ignition event triggers after wheel decoding, in same style as tooth logger

Only shows raw input pulses on modes with no decoding (fuel only, EDIS, etc)

For modes with wheel decoding, only useful to diagnose wheel decoder configuration mistakes (usually in MS1/Extra)

Common problems: Noise

Random stray pulses

Common problems: Phantom Tooth

Consisten issue caused by small noise pulse in missing tooth range

Two main VR conditioner families in the MegaSquirt line

Bowling & Grippo design

Used on V3.0, V3.57 main board, older MicroSquirt

MAX9926 Used on MS3-Pro,

MicroSquirt V3.0

Adjusting the B&G conditioner

Conditioner works on current, not voltage R56 adjusts threshold level that triggers the

conditioner R52 adjusts hysteresis level Can also be adjusted by placing a resistor inline with VR sensor

Common adjustments

Loss of signal at high RPM: Increase threshold voltage (R56) Install 10K resistor in line with VR sensor

(usually done with 36-1 or 60-2 trigger wheels with phantom tooth issue)

MAX9926 conditioner

Works on voltage, not current Double ended: compares voltage on + and

– terminals Ordinarily, negative terminal biased to 2.5

volts Signal clipped at 0 to 5 volts Adaptive based on peak voltages

Adjusting the MAX9926 circuit

To deal with noise at high RPM, put a 5K to 10K resistor across the terminals of the sensor

Triggering threshold can be increased by running a resistor from negative terminal to signal ground

Smaller resistor values increase offset, so a larger resistor is a less drastic change