From HOUGD@mdh-bemidji.health.state.mn.usFri Jan 12 11:28:13 1996 Date: Thu, 11 Jan 1996 21:57:25 -0600 From: Dan Houg To: Multiple recipients of list Subject: Testing Bosch O2 sensors. The following is exerpted from an article that appeared in the June 1995 issue of Motor Service. [question was posed on testing the sensor] Bosch offers a very straight forward procedure that begins with the sensor isolated from the computer. Warm up the engine, disconnect the sensor's pigtail from the harness and attach it directly to your [digital] meter or tester. To check rich response, hold 2,500 rpm and add propane to the intake (convenient hose and valve setups are available for this) until speed drops by 200 rpm. Or, pull and plug the vacuum hose to the fuel pressure regulator, which will increase psi and richen the blend. You should see the reading jump to .9V or more. If reaction is slow, or that voltage is never reached, try running it at 3,000 rpm for a few minutes, then check again. No improvement means you buy a new sensor. Then, test lean response. Introduce a small vacuum leak, say by removing an accessory hose, and watch the reading. If it drops to .2V or lower in less than one second, the sensor's okay. If it falls sluggishly, or you never see it get down to .2V, give it the 3,000 rpm treatment and try again, but it's probably time for replacement. Reconnect the pigtail to put the sensor back in touch with the system [ignition off], then tap your meter into the signal wire, maintain 1,500 rpm, and you should see rapidly changing reading that average somewhere around half a volt as the computer keeps adjusting the blend. Deciding whether or not response is slow enough to justify replacement requires some judgement. a common rule of thumb for minimum activity is eight trips across the rich/lean line in ten seconds, and sometimes you can find specs for cross-counts. From HOUGD@mdh-bemidji.health.state.mn.usFri Jan 12 11:31:33 1996 Date: Thu, 11 Jan 1996 22:07:14 -0600 From: Dan Houg To: Multiple recipients of list Subject: Re: Testing Bosch O2 sensors.addendum re-reading my post i see that article forgot to emphasize an important point: Have the ignition off when disconnecting or connecting the O2 sensor. This is important for 2 reasons: 1- it protects the computer from any transient voltage spikes during the connecting, and 2- the ECU can store mixture information if the sensor is disconnected/connected while the engine is running and throw off your rich/lean tests. -dan