Engine Controls - Diagnostic Methods (Except Diesel & Hybrid): Other Mercury Montego III

Vehicle Check/Preparation

Before using the diagnostic tool to carry out any test, refer to IMPORTANT SAFETY NOTICE and the necessary visual checks listed below.

Visual Checks

1. Inspect the air cleaner and inlet duct.
2. Check all engine vacuum hoses for damage, leaks, cracks, kinks, and proper routing
3. Check the electronic engine control (EEC) system wiring harness for proper connections, bent or broken pins, corrosion, loose wires, and proper routing.
4. Check the powertrain control module (PCM), sensors, and actuators for physical damage
5. Check the engine coolant for proper level and mixture.
6. Check the transmission fluid level and quality.
7. Make all necessary repairs before continuing with the Quick Test.

Vehicle Preparation

1. Carry out all safety steps required to start and run vehicle tests. Apply the parking brake, place the gear selector lever firmly into the PARK position on automatic transmission vehicles or NEUTRAL on manual transmission vehicles, and block the drive wheels.
2. Turn off all electrical loads such as radios, lamps, A/C, blower, and fans.
3. Start the engine and bring it up to the normal operating temperature before running the Quick Test.

Generic OBD PID List

GENERIC OBD PID LIST

Ford PID List

FORD PID LIST

Making Changes to the VID Block

A PCM which is programmed may require changes to be made to certain VID information to accommodate the vehicle hardware. Refer to PCM/Module Reprogramming on the diagnostic tool.

Drive Cycle Recommendations

1. Most OBD monitors complete more readily using a steady foot driving style during cruise or acceleration modes. Operating the throttle in a smooth fashion minimizes the time required for monitor completion.
2. The fuel tank level should be between 1/2 and 3/4 full with 3/4 full being the most desirable.
3. The evaporative monitor can only operate during the first 30 minutes of engine operation. When executing the procedure for this monitor, stay in part throttle mode and drive in a smooth fashion to minimize fuel slosh.
4. When bypassing the EVAP engine soak times, the PCM must remain powered (key ON) after clearing the continuous diagnostic trouble codes (DTCs) and relearning emission diagnostic information.

For best results, follow each of the following steps as accurately as possible

DRIVE CYCLE RECOMMENDATIONS

Recreating the Fault

Recreating the fault is the first step in isolating the cause of the intermittent symptom. A thorough investigation should start with the customer information worksheet located in the Introduction. If freeze frame data is available, it may help in recreating the conditions at the time of a malfunction indicator lamp diagnostic trouble code (MIL DTC). Listed below are some of the conditions for recreating the fault

RECREATE FAULT - CONDITIONS

Accumulating PCM Data

PCM data can be accumulated in a number of ways. This includes circuit measurements with a digital multimeter (DMM) or diagnostic tool PID data. Acquisition of PCM PID data using a diagnostic tool is one of the easiest ways to gather information. Gather as much data as possible when the fault is occurring to prevent improper diagnosis. Data should be accumulated during different operating conditions and based on the customer description of the intermittent fault. Compare this data with the known good data values located in in the TYPICAL DIAGNOSTIC REFERENCE VALUES . This will require recording data in four conditions for comparison: 1) KOEO, 2) Hot Idle, 3) 48 km/h (30 mph), and 4) 89 km/h (55 mph).

Analyzing Data from Playback of Stored PIDs

Look for abnormal events or values that are clearly incorrect. Inspect the signals for abrupt or unexpected changes. For example, during a steady cruise most of the sensor values should be relatively stable. Sensors such as throttle position (TP), mass air flow (MAF), and RPM that change abruptly when the vehicle is traveling at a constant speed are clues to a possible fault area.

Look for an agreement in related signals. For example, if TP is changed during acceleration, a corresponding change should occur in idle air control (IAC), RPM, and SPARK ADV PID.

Make sure the signals act in proper sequence. An increase in RPM after the TP is increased is expected. However, if the RPM increases without a TP change, a fault may exist.

Table Format (Scheme 1): Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the values. (Refer to the following TP example). Notice the major jump in the TP voltage while scrolling through the information. This example would require a smooth and progressive accelerator pedal travel during a key on and engine off mode.

Graph Format (Scheme 2): Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the linear lines showing the transformation of values to the line graph. This example would require smooth progressive accelerator pedal pressure with the key on and the engine off.

Scheme 1

Scheme 2

Peripheral Inputs

Some signals may require certain peripherals or auxiliary tools for diagnosis. In some cases, these devices can be inserted into the measurement jacks of the diagnostic tool or multimeter. For example, connecting an electronic fuel pressure gauge to monitor and record the fuel pressure voltage reading and capturing the data would help find the fault.

Comparing PCM Data

After the PCM values are acquired, it is necessary to determine the fault area. This typically requires the comparison of the actual values from the vehicle to the typical values from the TYPICAL DIAGNOSTIC REFERENCE VALUES . The charts apply to different vehicle applications (engine, model, transmission).

Obtain Freeze Frame Data

Freeze frame data is helpful in duplicating and diagnosing adaptive fuel concerns. The data (a snapshot of certain PID values recorded at the time the DTC is stored in Continuous Memory) is helpful to determine how the vehicle was being driven when the fault occurred, and is especially useful on intermittent concerns. Freeze frame data, in many cases, will help to isolate possible areas of concern as well as rule out others. Refer to FREEZE FRAME DATA for a more detailed description of this data.

Using the LONGFT1 and LONGFT2 (Dual Bank Engines) PIDs

The LONGFT1/2 PIDs are useful for diagnosing fuel trim concerns. A negative PID value indicates that fuel is being reduced to compensate for a rich condition. A positive PID value indicates that fuel is being increased to compensate for a lean condition. It is important to know that there is a separate LONGFT value that is used for each RPM/load point of engine operation. When viewing the LONGFT1/2 PIDs, the values may change a great deal as the engine is operating at different RPM and load points. This is because the fuel system may have learned corrections for fuel delivery concerns that can change as a function of engine RPM and load. The LONGFT1/2 PIDs will display the fuel trim currently being used at that RPM and load point. Observing the changes in LONGFT1/2 can help when diagnosing fuel system concerns. For example

1. A contaminated MAF sensor will result in matching LONGFT1/2 correction values that are negative at idle (reducing fuel), but positive (adding fuel) at higher RPM and loads.
2. LONGFT1 values that differ greatly from LONGFT2 values will rule out concerns that are common for both banks (for example, fuel pressure concerns, MAF sensor, etc. can be ruled out).
3. Vacuum leaks will result in large rich corrections (positive LONGFT1/2 value) at idle, but little or no correction at higher RPM and loads.
4. A plugged fuel filter will result in no correction at idle, but large rich corrections (positive LONGFT1/2 value) at high RPM and load.

Air Measurement System

With this condition, the engine will run rich or lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. One possibility is that the mass of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. For example, with a contaminated MAF sensor, the engine will run lean at higher RPM because the PCM will deliver fuel for less air than is actually entering the engine.

Examples: MAF sensor measurement is inaccurate due to a corroded connector, contamination or dirty connector. A contaminated MAF sensor will typically result in a rich system at low airflows (PCM will reduce fuel) and a lean system at high airflows (PCM will increase fuel).

Vacuum Leaks/Unmetered Air

With this condition, the engine will run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is caused by unmetered air entering the engine, or due to a MAF malfunction. In this situation, the volume of air entering the engine is actually greater than what the MAF sensor is indicating to the PCM. Vacuum leaks will normally be most apparent when high manifold vacuum is present (for example, during idle or light throttle). If freeze frame data indicates that the fault occurred at idle, a check for vacuum leaks/unmetered air is the best starting point.

Examples: Loose, leaking, or disconnected vacuum lines, intake manifold gaskets, or O-rings, throttle body gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve, unseated engine oil dipstick.

Insufficient Fueling

With this condition, the engine will run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine. This condition will normally be apparent as the engine is under a heavy load and at high RPM, when a higher volume of fuel is required. If the freeze frame data indicates that the fault occurs under a heavy load and at higher RPM, a check of the fuel delivery system (checking fuel pressure with engine under a load) is the best starting point.

Examples: low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel supply lines), fuel injector concerns.

Exhaust System Leaks

In this type of condition, the engine will run rich of stoichiometry (14.7:1 air/fuel ratio) because the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. This condition is caused by oxygen (air) entering the exhaust system from an external source. The HO2S will react to this exhaust leak by increasing fuel delivery. This condition will cause the exhaust gas mixture from the cylinder to be rich.

Examples: Exhaust system leaks upstream or near the HO2S, poorly welded/leaking HO2S boss, malfunctioning secondary air injection system.

With this condition, the engine will run rich or lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. One possibility is that the mass of air entering the engine is actually less than what the MAF sensor is indicating to the PCM. For example, a contaminated MAF sensor, the engine will run rich at idle because the PCM will deliver fuel for more air than is actually entering the engine.

Examples: MAF sensor measurement inaccurate due to a corroded connector, contamination/dirt. A contaminated MAF sensor typically results in a rich system at low airflows (PCM will reduce fuel) and a lean system at high airflows (PCM will increase fuel).

Fuel System

With this condition, the engine runs rich of stoichiometry (14.7:1 air/fuel ratio), if the PCM is not able to compensate enough to correct for the condition. This situation causes a fuel delivery system that is delivering excessive fuel to the engine.

Examples

1. Fuel pressure regulator causes excessive fuel pressure (system rich at all airflows) fuel pressure is intermittent, going to pump deadhead pressure, then returning to normal after the engine is turned off and restarted.
2. Fuel pressure regulator vacuum hose off (causes excessive fuel pressure at idle, system rich at idle airflows).
3. Fuel pressure regulator diaphragm ruptured (fuel leaking into the intake manifold, system rich at lower airflows).
4. Fuel return line crimped/damaged (fuel pressure high, system rich at lower airflows).
5. Fuel injector leaks (injector delivers extra fuel).
6. EVAP canister purge valve leak (if the canister is full of vapors, introduces extra fuel).
7. Fuel rail pressure sensor (electronic returnless fuel systems) concern causes the sensor to indicate a lower pressure than actual. The PCM commands a higher duty cycle to the fuel pump driver module (FPDM), causing high fuel pressure (system rich at all airflows).

Air Inlet System

A restriction within any of the following components may be significant enough to be beyond the ability of the PCM to control stoichiometry resulting in a rich condition.

1. Air inlet tube
2. Air cleaner element
3. Air cleaner assembly
4. Resonators
5. Clean air tube

Base Engine

Engine oil contaminated with fuel can contribute to a rich running engine.

Open Circuit (Continuity)

Disconnect the PCM. Measure the harness resistance between the suspect circuit at the harness connector and the appropriate PCM harness connector pin or PCM breakout box (if available). The resistance must be less than 5 ohms.

Shorts to Ground

Measure the harness resistance between the suspect circuit at the harness connector and a reliable ground (B-, chassis gnd, or PWR GND at the PCM breakout box, if available). The resistance must be greater than 10,000 ohms.

Shorts to Power

Key on to power up the circuit. Measure the voltage between the suspect circuit at the harness connector and a reliable ground. The voltage must be less than 1.0 volt.