OBD II Stumbles & Hesitates
OBD II Occurrences of Stumbling & Hesitation
OBD II engines should not suffer from even slight stumbling and hesitation, due to the ongoing varying parameters on-the-go. That is defying the scope of the Powertrain’s Control Module (PCM) in the first place – PCM main function is to vary continuously the engine’s parameters for optimum running.
Engine hesitation, stumbling, misfiring and lack of power under load are normally the result of a lean engine. This can be through the following:
- Lack of fuel
- Excessive air
- Engine misfires
Throttle Position Sensor (TPS):
This is a common problem. The TPS usually wear out on the idle or just above the idle position, thus giving false data to the PCM. The TPS function is to tell the PCM how open the throttle body is at that instance so the fuel/air mixture is adjusted accordingly.
TPS fault codes for a TPS malfunction will show up as P0120 to P0124 and / or P0222 to P0229 on the diagnostic obd2 scanner.
Fuel Injector Blockage:
Partially blocked fuel injectors through fuel gumming will cause lack of fuel mist volume (spray) required by the engine’s need at that instant. The current air volume in the intake will dilute the mixture even more.
Injectors will need to be removed, cleaned up with injector cleaner spray and tested before reinstalling them to the engine. If they still fail to perform they will need cleaning at an injector / fuel pump specialist. These will be dismantled and cleaned through a special ultrasonic machine. The injector’s internal bore and needle are checked ‘ring’ wear. Finally they are tested and calibrated to ensure fuel stability across the injector’s opening range.
Bad injector symptoms is when the injector doesn’t keep a consistent spray flow when testing on the idle position, or injector droplets flow out of the injector instead of fine spray mists. This problem usually is accompanied by stumbling and hesitation and can also cause misfiring occurrences.
Injector fault codes for lean fuel will show up as P0171 or P0174 on the diagnostic obd2 scanner.
Other known problems which cause stumbling on acceleration can be:
- Vacuum leaks
- Low fuel pressure
- Weak spark due to bad coil/s – Might also be a low primary input voltage on the coil (wire resistance)
- Retarded ignition timing
- Contaminated fuel
When any of the faults above are flagged up on the OBD II system the ‘Check Engine’ light should go On. The only way to retrieve these Data Trouble Codes is by doing a scantest with a diagnostic obd2 scanner, or an obd2 reader. The faults should only be reset after the offending faults are examined and fixed. If not they will soon reappear, the bad engine’s performance will not improve just by a reset.
