If you unplugged the sensor, of course you will still get the same error code. Unplugging the sensor is intended to eliminate it as a potential source of driveability concerns.
Here's how to troubleshoot the MAP/BP sensor and circuit. It requires some specialized equipment that most people won't have. It would be cheaper to replace the sensor than to buy the frequency counter. The Wells SU216 (89 SHO) sells for $55 special order from AutoZone. Actron makes a Map and MAF (and more)sensor tester that is sold through Sears for about $90.
Test voltage supply at connector first:
- Disconnect the sensor.
- Connect meter to two outside terminals.
- Turn ignition to on. Voltage reading should be between 4 and 6 volts. If not, troubleshoot the VREF and ground circuits.
To test performance of the sensor itself, backprobe the center connector and connect the frequency counter between there and battery ground.
Using a hand vacuum pump, apply vacuum to the vacuum hose connection while monitoring the output of the sensor as indicated by the frequency counter. At 30 in-HG (average sea-level pressure), the output should be around 159 Hz. For each 1.2 in-Hg decrease in pressure at the sensor, the frequency should drop by 3.5-3.6 Hz.
At typical atmospheric pressures seen by most cars at typical altitudes and under extreme weather conditions, pressures encountered would only vary between 27 and 31 in-Hg resulting in a normal operating frequency range of 151 to 162.4 Hz.
If the VREF and MAP/BP both test good, then either the wiring to the PCM or the PCM itself is bad.
That was derived from the Probst manual, pp 296-297.
As for the 87, does the fuel pump run? There is a signal line that runs from pin 5 of the IRCM (Fuel Pump Output Drive) to the inertia switch and also back to the PCM pin 19 (FPM -Fuel Pump Monitor). This allows the PCM to monitor if the IRCM has switched the FP on. My hunch, if the FP is working properly, that this may correspond to the three digit code posted by later models when you stall the engine. Not sure, but I see no way that the PCM can monitor the primary supply circuit to the FP circuit other than that one.
As for your KOER test results, they are invalid. The engine must be at operating temp as a prerequisite to testing. Further, the engine must be run at 1500-2000 RPM for several minutes immediately prior to testing to pre-heat the HEGOs.
Re-run the test after proper setup, then practice your timing for the goose test and other operator inputs.
Steve
<small>[ April 16, 2003, 07:30 AM: Message edited by: projectSHO89 ]</small>
