I have a 2001 mazda 626 and when im driving it skips sometimes
Description
Engine stops unexpectedly at beginning of acceleration or during acceleration
Engine stops unexpectedly while cruising
Engine speed fluctuates during acceleration or while cruising
Engine misses during acceleration or cruising
Vehicle bucks or jerks during acceleration, while cruising, or upon deceleration
Momentary pause at the beginning of acceleration or during acceleration
Momentary minor irregularity in engine output
Possible Causes
Air leakage from intake-air system parts
Improper operation of idle air control valve
Crankshaft sensor circuit malfunction
Camshaft sensor circuit malfunction
Spark leakage from ignition coil
PCV valve malfunction
Restriction in exhaust system
Open or short circuit in fuel pump and related harness
Improper fuel pressure
Fuel leakage from injector
Improper A/C system operation
Purge solenoid valve malfunction
EGR valve malfunction
EGR solenoid malfunction
Low engine compression
Vacuum leakage
Fuel pump control relay and resistor
Poor fuel quality
Air filter restriction
Electrical connector disconnection
No battery power supply to ECU or poor ground
Fuel pump mechanical malfunction
Clogged injector
Diagnostic Procedure
1. Verify vacuum hose connections, check the air filter, check for leakage or restriction of the intake-air system, ensure proper sealing of intake manifold and components attached (e.g. EGR, IAC), examine ignition components, fuel quality, and electrical connections. Are all items okay?
Yes - Go to next step
No - Service as required.
2. Check for stored OBD-II error codes. Are there any stored codes?
Yes - Go to appropriate DTC test
No - Go to next step
3. Is engine overheating?
Yes - Go to Symptom #10 for "engine overheats"
No - Go to next step
4. Connect an OBD-II scan tool capable of logging sensor output and drive the vehicle. Are engine speed (RPM), mass-airflow (MAF), throttle position (TP), and vehicle speed (VSS) PIDs within specifications?
Yes - Go to next step
No - Inspect crankshaft position sensor (RPM) circuit, mass airflow sensor (MAF) circuit, throttle position sensor (TP) circuit, and vehicle speed sensor (VSS) circuit.
5. Visually inspect the crankshaft position sensor and the teeth on the crankshaft pulley. Are these components okay?
Yes - Go to next step
No - Service as required
6. Measure the gap between the crankshaft position sensor and the teeth of the crankshaft pulley (specification: 0.5-1.5mm). Is the gap within specification?
Yes - Go to next step
No - Adjust crankshaft position sensor
7. Check spark plug condition. Are spark plugs wet, grayish white, or covered with carbon soot?
Yes - If wet or sooty, check for leaky fuel injector
No - Install spark plugs on original cylinders then go to next step
8. Remove PCV valve and shake PCV valve. Does the valve rattle?
Yes - Go to next step
No - Replace PCV valve
9. Verify that the throttle lever is resting on the throttle valve stop screw and/or throttle valve orifice plug. Are there any faults present?
Yes - adjust as necessary
No - Go to next step
10. Is there an exhaust restriction?
Yes - Inspect exhaust system
No - Go to next step
11. Check fuel pressure between fuel filter and fuel rail. Connect a jumper wire between the F/P terminal at the engine bay DLC connector and ground. Is the fuel line pressure within specification (280-330kPa or 41-48psi) with the ignition switch on?
Yes - Go to next step
No - If there is no or low pressure, check the fuel pump circuit, control relay and resistor, fuel pump relief valve as well as for fuel leakage inside the fuel pressure regulator and for a restricted main fuel line. If the fuel pressure is too high, check the fuel pressure regulator, the fuel pump control relay and resistor, and for a clogged fuel return line
12. Does fuel pressure increase when the accelerator is depressed?
Yes - Go to next step
No - Examine the fuel pressure regulator control (PRC) solenoid
13. Skip to the next step if the symptom occurs with or without the A/C running. If symptom occurs only with A/C operation, connect a pressure gauge to the A/C line and measure both low and high side pressures. Are the pressures within specifications?
Yes - Go to next step
No - Check the refrigerant charging amount, A/C pressure switch operation, condenser fan operation, and the A/C relay
14. Skip to the next step if the symptom occurs with or without cruise control operation. If symptom occurs only during cruise control operation, inspect the cruise control system. Is cruise control system operating properly?
Yes - Go to next step
No - Repair cruise control system
15. Is the evaporative emissions purge control system okay?
Yes - Go to next step
No - Check if purge control solenoid sticks open mechanically. Inspect the evaporative emissions control system.
16. Visually inspect the camshaft pulley, is the camshaft pulley okay?
Yes - Go to next step
No - Replace camshaft pulley
17. With the engine idling, disconnect the vacuum hose from the EGR valve and plug it. Is the engine condition improved?
Yes - Check for a stuck EGR solenoid vacuum valve, vent valve, and solenoid valve connector terminals
No - Check if the EGR valve moves smoothly. If yes, go to next step. If no, replace the EGR valve
18. Is the air-bypass valve actuator okay?
Yes - Go to next step
No - Replace air-bypass valve actuator
19. Check engine compression with a cylinder compression test tool. Is the engine compression within specifications?
Yes - Verify valve timing and transmission operation
No - Check for cause
20. Verify test results
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