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Troubleshooting Engine Driveability Problems: Surging or Misfiring

How To Diagnose Surging or Misfiring Engines


Symptom: The engine surges or misfires while moving.
The engine seems to start fine and will normally accelerate fine. As you are driving and maintaining a steady speed, the engine seems to "speed up" slightly or it seems to miss and buck.

Possible causes:

  1. If you have a carburetor (there are still a few out there), the choke may not be set properly, or the choke may not be working correctly.
    The fix: Check the choke plate and make sure it is opening completely.
  2. The engine may be running too hot.
    The fix: Check and repair cooling system.
  3. The fuel pressure regulator may be operating at low pressure.
    The fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
  4. The ignition timing may be set wrong.
    The fix: Adjust ignition timing.
  5. Ignition system problem.
    The fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
  6. There may be a fault in the computerized engine control system: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
  7. The fuel filter may be partially clogged.
    The fix: Replace the fuel filter.
  8. Torque converter (automatic transmission only) may not be locking at the right time, or it may be slipping.
    The fix: Check lock up circuit or replace torque converter. (Not a DIY job)
  9. There may be a vacuum leak.
    The fix: Check and replace vacuum lines as required.
  10. Possible internal engine problems.
    The fix: Check compression to determine engine condition.
  11. EGR valve may be stuck open.
    The fix: Replace EGR valve.
  12. Drive axles may be loose or worn.
    The fix: Check and replace CV/universal joints as required.
  13. The fuel injectors may be dirty.
    The fix: Clean or replace fuel injectors.
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