NO.11 ENGINE STALLS/QUITS, ENGINE RUNS ROUGH, MISSES, BUCK/JERK, HESITATION/STUMBLE, SURGES [YF (2.0L Zetec)]


11	ENGINE STALLS/QUITS - ACCELERATION/CRUISE ENGINE RUNS ROUGH - ACCELERATION/CRUISE MISSES - ACCELERATION/CRUISE BUCK/JERK - ACCELERATION/CRUISE/DECELERATION HESITATION/STUMBLE - ACCELERATION SURGES - ACCELERATION/CRUISE
DESCRIPTION	• Engine stops unexpectedly at the beginning of acceleration or during acceleration. • Engine stops unexpectedly while cruising. • Engine speed fluctuates during acceleration or cruising. • Engine misses during acceleration or cruising. • Vehicle bucks/jerks during acceleration, cruising, or deceleration. • Momentary pause at beginning of acceleration or during acceleration • Momentary minor irregularity in engine output
POSSIBLE CAUSE	• Improper A/C system operation • Erratic signal or no signal from CMP sensor • Air leakage from intake-air system parts • Purge valve malfunction • IAC valve improper operation • EGR valve malfunction • Erratic signal from CKP sensor • Low engine compression • Vacuum leakage • Poor fuel quality • Main relay intermittent malfunction • Throttle body malfunction • Engine overheating • Erratic signal to ignition coil • Improper air/fuel mixture ratio control operation • Improper variable tumble control operation • Erratic signal to ignition coil • Air cleaner restriction • PCV valve malfunction • Fuel vapor vent valve malfunction • Fuel flow into evaporative purge hose • Improper valve timing due to jumping out timing belt • Restriction in exhaust system • Intermittent open or short circuit in fuel body pump circuit • Inadequate fuel pressure • Inertia fuel shutoff (IFS) switch malfunction • Fuel pump mechanical malfunction • Check valve (two-way) malfunction (integrated with fuel tank) • Fuel leakage from fuel injector • Fuel injector clogging • Fuel line restriction or clogging • Pressure regulator malfunction (built-in fuel pump unit) • TP sensor misadjustment • Intermittent open or short circuit of MAF sensor, TP sensor and VSS • Clutch slippage (MTX) • ATX malfunction (ATX) • Loose attaching bolts or worn engine mounts • ATX related part malfunction (ATX) Warning The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read the following warnings before performing any fuel system-related procedures: • Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always keep sparks and flames away from fuel. • Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or death and damage. Fuel can also irritate skin and eyes. To prevent this, always complete "BEFORE SERVICE PRECAUTION" and "AFTER SERVICE PRECAUTION" described in this manual. (See BEFORE SERVICE PRECAUTION [YF (2.0L Zetec)].) (See AFTER SERVICE PRECAUTION [YF (2.0L Zetec)].) Caution • Disconnecting/connecting quick release connectors without cleaning them may possibly cause damage to the fuel pipe or quick release connector. Always clean the quick release connector joint area before disconnecting/connecting, and make sure that it is free of foreign material.


STEP	INSPECTION	RESULTS	ACTION
1	Verify for the following: • Vacuum connection • Air cleaner element • No air leakage from intake-air system • No restriction of intake-air system • Proper sealing of intake manifold and components attached to intake manifold: such as EGR valve, IAC valve • Ignition wiring • Fuel quality (e.g. proper octane, contamination, winter/summer blend) • Electrical connections • Smooth operation of throttle valve Are all items normal?	Yes	Go to the next step.
1		No	Service if necessary. Repeat Step 1.
2	Connect the WDS or equivalent to the DLC-2. Retrieve any continuous memory, KOEO and KOER DTCs using the WDS or equivalent. If stall, condition exists retrieve continuous memory and KOEO DTCs. Are any DTCs displayed?	Yes	DTC is displayed: Go to the appropriate DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
2		No	No DTC is displayed: Go to the next step.
3	Is the engine overheating?	Yes	Go to symptom troubleshooting "No.17 Cooling system concerns - Overheating".
3	Is the engine overheating?	No	Go to the next step.
4	Connect the WDS or equivalent to the DLC-2. Access the RPM, VPWR, MAF, TP and VSS PIDs. Drive the vehicle with monitoring the PIDs. Are the PIDs within specifications? (See PCM INSPECTION [YF (2.0L Zetec)].)	Yes	Go to the next step.
4		No	RPM PID: Inspect the CKP sensor and related wiring harness for such as vibration, intermittent open/short circuit. VPWR PID: Inspect for open circuit intermittently. MAF PID: Inspect for intermittent open circuit of the MAF sensor and related wire harness. TP PID: Inspect if output signal from the TP sensor changes smoothly. VSS PID: Inspect for intermittent open circuit of the VSS and related wire harness.
5	Visually inspect the CKP sensor and crankshaft pulley teeth. Are the CKP sensor and crankshaft pulley teeth normal?	Yes	Go to the next step.
5		No	Replace the malfunctioning part.
6	Measure the gap between the CKP sensor and crankshaft pulley teeth. Specification 0.5-1.9 mm {0.020-0.75 in} Is the gap within specification?	Yes	Go to the next step.
6		No	Adjust the CKP sensor.
7	Inspect the spark plugs. Are any spark plugs wet, covered with carbon, or grayish white?	Yes	Spark plug is wet or covered with carbon: Inspect for fuel leakage from the fuel injector. Spark plug is grayish white: Inspect the fuel injector for clogging.
7		No	Install the spark plugs on original cylinders. Go to the next step.
8	Remove and shake the PCV valve. Does the PCV valve rattle?	Yes	Go to the next step.
8	Remove and shake the PCV valve. Does the PCV valve rattle?	No	Replace the PCV valve.
9	Verify that the throttle lever rests on throttle valve stop screw and/or throttle valve orifice plug. Is the lever in correct position?	Yes	Go to the next step.
9		No	Adjust if necessary.
10	Visually inspect for deformed exhaust system parts. Is there any deformed exhaust system part?	Yes	Replace the part.
10		No	Go to the next step.
11	Inspect the inertia fuel shutoff (IFS) switch. Is the IFS switch okay?	Yes	Go to the next step.
11		No	Replace the IFS switch.
12	Install a fuel pressure gauge between the fuel pipe and fuel distributor. Connect the WDS or equivalent to the DLC-2. Turn the fuel pump on using the FP PID. Is the fuel line pressure correct? (See FUEL LINE PRESSURE INSPECTION [YF (2.0L Zetec)].)	Yes	Go to the next step.
12		No	Zero or low: Inspect the fuel pump and the fuel pump relay related circuit. Inspect the fuel line for clogging. • If there is no malfunction, replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [YF (2.0L Zetec)].) High: Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [YF (2.0L Zetec)].)
13	Visually inspect for fuel leakage at the fuel injector, O-ring, and fuel line. Service if necessary. Is the fuel line pressure held after the FP PID is turned off? (See FUEL LINE PRESSURE INSPECTION [YF (2.0L Zetec)].)	Yes	Go to the next step.
13		No	Inspect the fuel injector. • If the fuel injector is normal, replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [YF (2.0L Zetec)].)
14	Note • The following test is for engine stall with the A/C on. If other symptom exists, go to the next step. Connect a pressure gauge to the A/C low and high pressure lines. Turn the A/C on and measure the low side and high side pressure. Are the pressures within specifications? (See REFRIGERANT SYSTEM TESTS.)	Yes	Go to the next step.
14		No	If the A/C is always on, go to symptom troubleshooting "No.24 A/C is always on or A/C compressor runs continuously". (See NO.24 A/C IS ALWAYS ON OR A/C COMPRESSOR RUNS CONTINUOUSLY [YF (2.0L Zetec)].) For other symptoms, inspect the following: • Refrigerant charging amount • Condenser fan operation
15	Connect the WDS or equivalent to the DLC-2. Warm up the engine and idle it. Access the O2S11 PID. Is the O2S11 PID normal? • More than 0.45 V when the accelerator pedal is suddenly depressed: rich condition. • Less than 0.45 V during fuel cut: lean condition.	Yes	Go to the next step.
15		No	Inspect and repair or replace the front HO2S, wiring harness, connector or terminal, then go to the next step. (See HEATED OXYGEN SENSOR (HO2S) INSPECTION [YF (2.0L Zetec)].)
16	Inspect the evaporative purge hose between the fuel tank and the purge valve. Dose fuel flow into the evaporative purge hose?	Yes	Inspect the check valve (two-way).
16		No	Go to the next step.
17	Disconnect the vacuum hose between the purge valve and the intake manifold from the purge valve side. Plug the open end of vacuum hose. Drive the vehicle. Does the engine condition improve?	Yes	Go to the next step. Inspect if the purge valve is stuck open mechanically. Inspect the evaporative emission control system.
17		No	Go to the next step.
18	Visually inspect the CMP sensor and camshaft pulley projections. Are the CMP sensor and projections of camshaft pulley projections normal?	Yes	Go to the next step.
18		No	Replace the malfunctioning part.
19	Inspect the variable tumble control operation. Is the variable tumble control normal?	Yes	Go to the next step.
19		No	Replace or replace the malfunctioning part.
20	Inspect the EGR system. (See EGR System Operation Inspection.) Is EGR system normal?	Yes	Go to the next step.
20		No	Replace the malfunctioning part.
21	Is engine compression correct?	Yes	Inspect the following: • Valve timing • Clutch (MTX) • Internal ATX components (ATX) • EGR valve (mechanical stuck) • Engine mounts • Check valve (two-way) • Fuel vapor vent valve • ATX related parts (ATX)
21	Is engine compression correct?	No	Inspect for cause.
22	Verify test results. • If normal, return to the diagnostic index to service any additional symptoms. (See ENGINE SYMPTOM TROUBLESHOOTING [YF (2.0L Zetec)].) • If any malfunction remains, inspect related service information and, repair or diagnosis accordingly. - If the vehicle is repaired, troubleshooting completed. - If the vehicle is not repaired or additional diagnostic information is not available, replace the PCM. (See PCM REMOVAL/INSTALLATION [YF (2.0L Zetec)].)