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If an engine does not run well, there are often several possible causes, depending upon the symptom. The more information you can gather about the vehicle, the symptom and its occurrence, the easier your troubleshooting procedures will be. Try to determine the following;

What type of problem is it?

  • misfire
  • hesitation
  • surging
  • lack of power
  • other

When does it happen?

  • during acceleration
  • during deceleration
  • during steady throttle
  • when stopped
  • under a heavy load
  • all of the time

Under what conditions does it occur?

  • when the engine is cold
  • when the engine is hot
  • at all engine temperatures
  • in neutral
  • only in one gear
  • at what rpm
  • sporadically
  • only in the rain or wet conditions

How did the problem develop?

  • all at once
  • it got progressively worse over time
  • it started after an accessory was installed (air filter, exhaust, etc.)
  • it started after work was performed on the engine

Has anyone else worked on the vehicle?

  • are they a qualified technician
  • were they doing regular maintenance
  • were they making repairs unrelated to the problem
  • were they trying to diagnose the problem

Use the following chart to help narrow down the possible causes of the problem. The cause could be Electrical (E), Fuel related (F) or Mechanical (M), or a combination of possibilities.


Condition Misfire Hesitation Surging Lack of power
Acceleration E or F E or F E or F E, F or M
Deceleration F N/A N/A N/A
Steady throttle E or F N/A F E, F or M
Stopped E or F N/A F or M N/A
Under a heavy load E or F E, F or M F F or M



Cylinder Head / Valves

  • Poor cylinder head operation can be diagnosed by a compression test or by tracing engine top-end noises.

Poor performance at idle speed

  • Compression too low

Compression too low

  • Incorrect valve clearance adjustment
  • Burned or bent valves
  • Incorrect valve timing
  • Broken valve spring
  • Poor valve and seat contact
  • Leaking cylinder head gasket
  • Warped or cracked cylinder head
  • Poorly installed spark plug

Compression too high

  • Excessive carbon build-up in combustion chamber

White smoke from exhaust muffler

  • Worn valve stem or valve guide
  • Damaged valve stem seal

Abnormal noise

  • Incorrect valve clearance adjustment
  • Sticking valve or broken valve spring
  • Damaged or worn camshaft
  • Worn cam chain guide
  • Worn camshaft and rocker arm

Cylinder and Piston

  • When hard starting or poor performance at low speed occurs, check the crankcase breather for white smoke. If white smoke is found, it means that the piston rings are worn, stuck or broken.

Compression too low or uneven compression

  • Worn, stuck or broken piston rings
  • Worn or damaged piston rings

Compression too high

  • Excessive carbon build-up in combustion chamber or performance modifications like a high compression piston etc.

Excessive smoke from exhaust muffler

  • Worn or damaged cylinder and piston
  • Worn or damaged piston rings

Abnormal noisy piston

  • Worn cylinder, piston and piston rings
  • Worn piston pin hole and piston pin

Crankshaft, Transmission/Final Drive Gears

Abnormal engine noise

  • Excessive crank journal bearing play
  • Excessive crankpin bearing play
  • Excessive transmission bearing play

Engine starts but Vehicle won‘t move

  • Damaged transmission
  • Seized or burnt transmission

Oil leaks

  • Oil too thin
  • Worn or damaged oil seal o-ring or gasket

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