10. Tips, Tricks and Troubleshooting
10.1 General measurement requirements
The LM-1 measures the air-fuel-ratio by measuring the amount of oxygen in the exhaust for lean
conditions or the amount of unburned or partially burned fuel for rich conditions. An exhaust leak
will allow oxygen to enter the exhaust stream and therefore will measure leaner than the engine
is actually running. For correct measurement, air-leaks in the exhaust MUST be prevented under
all circumstances.
Missing ignitions where the air-fuel mixture does not light up also pump unburned oxygen into the
exhaust and cause the LM-1 to measure lean.
The only circumstance where the LM-1 will measure richer than the engine is running is if the
pressure in the exhaust tract is excessive and the engine is running on the rich side.
10.2 Vehicles with ‘smog-pumps’
Older fuel injected vehicles with a ‘smog-pump’ actually inject air in the exhaust stream to aid
their catalytic converter in the burn-up of unburned or partially burned fuels. This additional air will
make the exhaust look leaner than the engine is running. To accurately measure, install the LM-1
sensor up-stream of the outputs of the smog-pump. If this is not possible, temporarily disable the
smog-pump by removing its drive belt.
10.3 Measuring at the tail-pipe
On non-catalytic converter equipped vehicles it is possible to measure the air-fuel-ratio at the tail-
pipe. It is highly recommended to use the optional LM-1 Exhaust Clamp. Without it too much
outside air may enter the exhaust, especially at idle, to prevent correct measurements and
leading to a lean measurement. Sticking the sensor itself into the exhaust pipe can yield
inconsistent results because the sensor will not have outside air available as a reference gas and
its reaction time becomes so slow that the LM-1 will report a sensor timing error. The oxygen
sensor needs to have the back part of the sensor (where the wires enter the sensor) exposed to
outside air.
10.4 Single Cylinder Engines
These kinds of engines are difficult to measure at the tail-pipe. The oscillations of the exhaust
gas are so large that a lot of outside air enters the exhaust and prevents correct measurement.
Sometimes it helps to just wrap a piece of heat resistant cloth around the exhaust clamp to
prevent outside air from entering the exhaust.
10.5 Diesel Engines
Diesel Engines and gas turbines run at wide open throttle at all times. They do not have a throttle
but regulate power by the amount of injected fuel. The LM-1 can still be used, but measurements
at idle will read as lean.
10.5 Reference cell or Pump cell circuit open or shorted errors
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