OBD II MONITOR OPERATION
| Comprehensive Components Monitor | Major Monitors Non Fuel Control & Non Misfire | Major Monitors Fuel Control & misfire |
|---|---|---|
| (Includes All Engine Hardware Sensor, Switches, Solenoids, etc.) | (Monitors Entire Emission System) | (Monitors Entire System) |
| Most are one trip Faults | Most are Two Trips Faults | Two Trip Faults |
| Usually Turns on The Mill and Sets DTC After One Failure | Turns On The Mil and Sets DTC after Two Consecutive Failure | The Mil and Sets DTC After Two Consecutive Failure |
| Priority 3 | Priority 1 or 3 | Priority 2 or 4 |
| All Checked For Continuity | Done Stop Test = Yes | Fuel Control Monitor |
| Open | Oxygen Sensor Heater | Monitors Fuel Control |
| Short To Ground | Oxygen Sensor Response | System For |
| Short To Voltage | Catalytic Converter | Fuel System Lean |
| Inputs Checked For Rationality | Efficiency Except EWMA | Fuel System Rich |
| Outputs Checked For Functionality | Up to 6 test per trip and a one trip fault (SBEC) and two trip fault on (JTEC) | Requires 3 Consecutive Fuel System Good Trips to Extinguish the MIL |
| EGR System | Misfire Monitor | |
| Evaporative Emission System (purge and leak) | Monitors for Engine Misfire At | |
| Non-LDP | 4 X 1000 RPM Counter (4000 Revs) (Type B) | |
| LDP | **200 X 3 (600) RPM counter (Type A) | |
| Requires 3 Consecutive Global Good Trips to Extinguish the MIL* | Requires 3 Consecutive Global Good Trips to Extinguish the MIL* | Requires 3 Consecutive Global Good Trips to Extinguish the MIL |
| *40 Warm Up Cycles are required to erase DTCs after the MIL has been extinguished | ** Type A misfire is a one trip failure on pre-1999, 2 trip failure on 1999 and later. The MIL will illuminate at the first or second failure, based on MY. |
DESCRIPTION
The ORVR (On-Board Refueling Vapor Recovery) system consists of a unique fuel tank, flow management valve, fluid control valve, one-way check valve and vapor canister.
OPERATION
The ORVR (On-Board Refueling Vapor Recovery) system is used to remove excess fuel tank vapors. This is done while the vehicle is being refueled.
Fuel flowing into the fuel filler tube (approx. 1" I.D.) creates an aspiration effect drawing air into the fuel fill tube. During refueling, the fuel tank is vented to the EVAP canister to capture escaping vapors. With air flowing into the filler tube, there are no fuel vapors escaping to the atmosphere. Once the refueling vapors are captured by the EVAP canister, the vehicle's computer controlled purge system draws vapor out of the canister for the engine to burn. The vapor flow is metered by the purge solenoid so that there is no, or minimal impact on driveability or tailpipe emissions.
As fuel starts to flow through the fuel fill tube, it opens the normally closed check valve and enters the fuel tank. Vapor or air is expelled from the tank through the control valve and on to the vapor canister. Vapor is absorbed in the EVAP canister until vapor flow in the lines stops. This stoppage occurs following fuel shut-off, or by having the fuel level in the tank rise high enough to close the control valve. This control valve contains a float that rises to seal the large diameter vent path to the EVAP canister. At this point in the refueling process, fuel tank pressure increases, the check valve closes (preventing liquid fuel from spitting back at the operator), and fuel then rises up the fuel filler tube to shut off the dispensing nozzle.
Scheme 7
A PCV valve (1) using a rubber sealing O-ring (2) is used.
Scheme 8
The PCV valve is threaded into a metal fitting. The valve (2) is located at the rear of the left cylinder head.
Scheme 9
A typical enclosed crankcase ventilation system is (Scheme 9)
The PCV system operates by engine intake manifold vacuum. Filtered air is routed into the crankcase through the air cleaner hose. The metered air, along with crankcase vapors, are drawn through the PCV valve (4) and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow by gases to the intake system, reducing engine sludge formation.
The PCV valve contains a spring loaded plunger. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.
Scheme 10
When the engine is not operating or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve.
Scheme 11
During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.
Scheme 12
During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve.