ICP--Injection Control Pressure--IPR--Injection Pressure Regulator--and MFDES--Mass Fuel Desired: ICP should rise as IPR duty cyle increases; MFDES and IPR should rise at the same rate as load and/or demand increases (actual readings may not match); ie. ICP=500psi, IPR=12%, MFDES=10MG @500 RPM; ICP=900psi, IPR=22%, MFDES=20MG @1800RPM/cruise; ICP=1800psi, IPR=50%, MFDES=40MG @3000RPM/hard accel.
ICP--Injection Control Pressure--and RPM--CaMshaft Position Sensor: After 3 minutes at 3300 RPM, ICP pressure should be below 1400psi for Federal, 1250psi for California Emmisions, and 1500psi for 99.5. At idle, ICP should be 550-700psi for Federal, 400-600 for California and stable.
V PWR--Battery Voltage--RPM--CaMshaft Position sensor--ICP--Injection Control Pressure--FuelPW--Fuel Pulse Width: When starting V PWR should be above 10volts, ICP should be at least 500psi, at least 100RPM, and FuelPW 1mS-6mS. Once the PCM recognizes CMP speed and cylinder ID, FuelPW should default to 0.42mS, 0.60mS for 99 up, until ICP reaches starting pressure.
EOT--Engine Oil--and IAT--Intake Air Temperatures: After a cold soak, before starting EOT and IAT should be within 10 degrees of each other, Key On Engine Off.
BARO--Barometric--MAP--Manifold Absolute--and EBP--Exhaust BackPressures: All three should indicate atmospheric pressure (14.7psi at sea level) and read within 0.5 psi of each other, Key On Engine Off.
ICP--Injection Control Pressure--and ICP V--ICP Voltage: ICP should read 0psi, ICP V should read 0.20-0.25 volts, Key On Engine Off.
EBP--Exhaust BackPressure--MGP--Manifold Gauge Pressure--and RPM--CaMshaft Position Sensor: At full throttle in neutral, EBP should be below 28psi; At full throttle in fourth (manual) or third (auto) gear, MGP should be 15psi.
The PCM reads only voltage signals from the sensors. All readings which are not displayed in volts are what the PCM calculates those sensor inputs equal. In some cases, the PCM uses one voltage input to calculate a base line for other sensor readings. For example, BARO is used to calculate MAP/MGP base line. At sea level, calculates BARO at 14.7 PSI, so a MAP reading of 14.7 equals 0 PSI MGP. At an elevation of 5000 feet, BARO and MAP would be 12.1 PSI, so the MGP base line would be recaluclated to reflect 0 and not -2.6 PSI.
All ouputs are functions that the PCM is attempting to perform based on the inputs it is receiving. If there is an output device malfunction, the results may not be what the PCM is trying to achieve, but the output signal may still show normal. Some outputs may not match actual measurements. For example, the displayed duty cycle of the IPR may not match the actual duty cycle as viewed on a scope, or the displayed transmission control pressure output may not match the actual pressure on a test gauge.
Strategic displays like MFDES will change as the PCM detects changes in sensor inputs which may indictae changes in environment, such as altitude, or wear in the engine. This is part of the PCM's adaptive strategy, or "learning" capability.