|
| LinkExchange Member | Free Home Pages at GeoCities |
|
| LinkExchange Member | Free Home Pages at GeoCities |
FIRST A LITTLE INFORMATION ABOUT 02 SENSORS:
The O2 sensor helps keep the air/fuel mixture at a optimum 14.7:1 (stochiemetric) levels. In today's electronic fuel injected and three way catalytic convertors, the O2 sensor became a major control sensor. a proper operating O2 sensor will aid the catalytic operation and will control the air/fuel mixture. The O2 sensor is designed to measure the difference in oxygen between inside exhaust and outside air and generate a proportional electrical signal.
OPEN VS. CLOSED LOOP? Open and closed loop is a subject which has been misunderstood over the years! Open loop is when the O2 sensor signal is being ignored as a fuel control. Fuel mixture is controlled by pre-set or designed parameters described by the manufacture.
They are:
Coolant temperature
RPM
Engine load
Time and system overall condition must be considered!
A single wire O2 sensor starts operation at 600 degrees and a heated sensor starts
At 250 degrees. The operating range of the O2 sensor is 600 - 1550 degrees.
Control Testing
You can use O2 control testing for:
A. Diagnose engine combustion events with a single wire hook-up.
B. Determine engine fuel control and condition subsequent to any service.
C. Decrease driveability comebacks.
TESTING THE O2 SENSOR Since I do not know which kind of scope you will be using. First: you should make sure that you understand the operation of your Lab Scope And the proper way to use it. Some DSO use a 10:1 probe with a low pass filter. Hook the ground lead to a good ground near the O2 Sensor. Next back probe the O2 wire or use a BOB. Run the engine at fast idle until warm (2000 - 2200 RPM). The voltage will be low on the lab scope, less than 0.45 VDC, When the computer goes in close loop the reading will begin to cross count. 0.45 VDC is the cross over line. a reading under 0.45 is lean and any reading above 0.45 VDC is rich. With the engine running at about 2000 RPM, the 02 sensor voltage should rapidly change between 100 - 900 millivolts as the ECM hunts for the stochiemetric air/fuel ratio. You can use an open intake vacuum (brake booster or pcv hose) to force it lean and propane gas to force it rich. The maximum O2 sensor voltage with the system forced rich should be above 800 mV. The minimum O2 sensor voltage forced lean should be less than 150 mV. The maximum response time from rich-to-lean should be less than 100 ms.
On the 1 second\division scale, the transition trace should make a nearly vertical drop from maximum to minimum sensor voltage. The O2 sensor should respond to lean-to-rich transitions even faster than rich-to-lean transitions A good sensor should make the lean-to-rich transition in 50 ms or less.
Note: After replacing the O2 sensor, take a long test drive to relearn the Computer (ECM/PCM) because of the bad information of the old sensor.
Carlis Wilson
� 1997 [email protected]
