Engine will not start or is hard to start
1 ) Compression too low | |
Valve clearance out of adjustment. | Adjust. |
Worn valve guides or poor seating of valves. | Repair or replace. |
Mistimed valves. | Adjust. |
Excessively worn piston rings. | Replace. |
Worn-down cylinder bores. | Replace. |
Starter motor cranks too slowly. | See electrical section |
Poor seating of spark plugs. | Retighten. |
2) Plug not sparking | |
Fouled spark plugs. | Clean or replace. |
Wet spark plugs. | Clean and dry. |
Defective ignition coils. | Replace. |
Open or short in high-tension cord. | Replace. |
Defective CKP sensor. | Replace. |
Defective ECM. | Replace. |
Open-circuited wiring connections. | Repair or replace. |
3) No fuel reaching the intake manifold | |
Clogged fuel filter or fuel hose. | Clean or replace. |
Defective fuel pump. | Replace. |
Defective fuel pressure regulator. | Replace. |
Defective fuel injector. | Replace. |
Defective fuel pump relay. | Replace. |
Defective ECM. | Replace. |
Open-circuited wiring connections. | Check and repair. |
4) Incorrect fuel/air mixture | |
TP sensor out of adjustment. | Adjust. |
Defective fuel pump. | Replace. |
Defective fuel pressure regulator. | Replace. |
Defective TP sensor. | Replace. |
Defective CKP sensor. | Replace. |
Defective IAP sensor. | Replace. |
Defective ECM. | Replace. |
Defective ECT sensor. | Replace. |
Defective IAT sensor. | Replace. |
Engine idles poorly
Valve clearance out of adjustment. | Adjust. |
Poor seating of valves. | Replace or repair. |
Defective valve guides. | Replace. |
Worn down camshafts. | Replace. |
Too wide spark plug gaps. | Adjust or replace. |
Defective ignition coils. | Replace. |
Defective CKP sensor. | Replace. |
Defective ECM. | Replace. |
Defective TP sensor. | Replace. |
Defective fuel pump. | Replace. |
Imbalanced throttle valve or STV. | Adjust. |
Damaged or cracked vacuum hose. | Replace. |
Engine stalls often
1) Incorrect fuel/air mixture | |
Defective IAP sensor or circuit. | Repair or replace. |
Clogged fuel filter. | Clean or replace. |
Defective fuel pump. | Replace. |
Defective fuel pressure regulator. | Replace. |
Defective ECT sensor. | Replace. |
Defective thermostat. | Replace. |
Defective IAT sensor. | Replace. |
Damaged or cracked vacuum hose. | Replace. |
2) Fuel injector improperly operating | |
Defective fuel injectors. | Replace. |
No injection signal from ECM. | Repair or replace. |
Open or short circuited wiring connection. | Repair or replace. |
Defective battery or low battery voltage. | Replace or recharge |
3) Control circuit or sensor improperly operating | |
Defective ECM. | Replace. |
Defective fuel pressure regulator. | Replace. |
Defective TP sensor. | Replace. |
Defective IAT sensor. | Replace. |
Defective CKP sensor. | Replace. |
Defective ECT sensor. | Replace. |
Defective fuel pump relay. | Replace. |
4) Engine internal parts improperly operating | |
Fouled spark plugs. | Clean. |
Defective CKP sensor or ECM. | Replace. |
Clogged fuel hose. | Clean. |
Valve clearance out of adjustment. | Adjust. |
Noisy engine
1) Excessive valve chatter | |
Too large valve clearance. | Adjust. |
Weakened or broken valve springs. | Replace. |
Worn tappet or cam surface. | Replace. |
Worn and burnt camshaft journal. | Replace. |
2) Noise seems to come from piston | |
Worn down pistons or cylinders. | Replace. |
Combustion chambers fouled with carbon. | Clean. |
Worn piston pins or piston pin bore. | Replace. |
Worn piston rings or ring grooves. | Replace. |
3) Noise seems to come from cam chain | |
Stretched chain. | Replace. |
Worn sprockets. | Replace. |
Tension adjuster not working. | Repair or replace. |
4) Noise seems to come from clutch | |
Worn splines of countershaft or hub. | Replace. |
Worn teeth of clutch plates. | Replace. |
Distorted clutch plates, driven and drive. | Replace. |
Worn clutch release bearing. | Replace. |
Weakened clutch dampers. | Replace the primary driven gear. |
5) Noise seems to come from crankshaft | |
Rattling bearings due to wear. | Replace. |
Worn and burnt big-end bearings. | Replace. |
Worn and burnt journal bearings. | Replace. |
6) Noise seems to come from transmission | |
Worn or rubbing gears. | Replace. |
Worn splines. | Replace. |
Worn or rubbing primary gears. | Replace. |
Worn bearings. | Replace. |
7) Noise seems to come from water pump | |
Too much play on pump shaft bearing. | Replace. |
Worn or damaged impeller shaft. | Replace. |
Worn or damaged mechanical seal. | Replace. |
Contact between pump case and impeller. | Replace. |
Engine runs poorly in high speed range
1) Defective engine internal/electrical parts | |
Weakened valve springs. | Replace. |
Worn camshafts. | Replace. |
Valve timing out of adjustment. | Adjust. |
Too narrow spark plug gaps. | Adjust. |
Ignition not advanced sufficiently due to poorly | Replace ECM. |
working timing advance circuit. | |
Defective ignition coils. | Replace. |
Defective CKP sensor. | Replace. |
Defective ECM. | Replace. |
Clogged fuel hose, resulting in inadequate fuel | Clean and prime. |
supply to injector. | |
Defective fuel pump. | Replace. |
Defective TP sensor. | Replace. |
Defective STP sensor or STVA. | Replace. |
Clogged air cleaner element. | Clean or replace. |
2) Defective air flow system | |
Clogged air cleaner element. | Clean or replace. |
Defective throttle valve. | Adjust or replace. |
Defective secondary throttle valve. | Adjust or replace. |
Sucking air from throttle body joint. | Repair or replace |
Defective ECM. | Replace. |
Imbalanced throttle valve synchronization. | Adjust. |
3) Defective control circuit or sensor | |
Low fuel pressure. | Repair or replace |
Defective TP sensor. | Replace. |
Defective IAT sensor. | Replace. |
Defective CKP sensor. | Replace. |
Defective GP switch. | Replace. |
Defective IAP sensor. | Replace. |
Defective ECM. | Replace. |
TP sensor out of adjustment. | Adjust. |
Defective STP sensor and/or STVA. | Replace. |
Engine lacks power
1) Defective engine internal/electrical parts | |
Loss of valve clearance. | Adjust. |
Weakened valve springs. | Replace. |
Valve timing out of adjustment. | Adjust. |
Worn piston rings or cylinders. | Replace. |
Poor seating of valves. | Repair. |
Fouled spark plugs. | Clean or replace. |
Incorrect spark plugs. | Adjust or replace. |
Clogged injectors. | Clean or replace. |
TP sensor out of adjustment. | Adjust. |
Clogged air cleaner element. | Clean or replace. |
Imbalanced throttle valve synchronization. | Adjust. |
Sucking air from throttle valve or vacuum hose. | Retighten or replace |
Too much engine oil. | Drain out excess oil. |
Defective fuel pump or ECM. | Replace. |
Defective CKP sensor and ignition coils. | Replace. |
2) Defective control circuit or sensor | |
Low fuel pressure. | Repair or replace. |
Defective TP sensor. | Replace. |
Defective IAT sensor. | Replace. |
Defective CKP sensor. | Replace. |
Defective GP switch. | Replace. |
Defective IAP sensor. | Replace. |
Defective ECM. | Replace. |
Imbalanced throttle valve synchronization. | Adjust. |
TP sensor out of adjustment. | Adjust. |
Defective STP sensor and/or STVA. | Replace. |
Engine overheats
1) Defective engine internal parts | |
Heavy carbon deposit on piston crowns. | Clean. |
Not enough oil in the engine. | Add oil. |
Defective oil pump or clogged oil circuit. | Replace or clean. |
Sucking air from intake pipes. | Retighten or replace. |
Use incorrect engine oil. | Change. |
Defective cooling system. | See radiator section. |
2) Lean fuel/air mixture | |
Short-circuited IAP sensor/lead wire. | Repair or replace. |
Short-circuited IAT sensor/lead wire. | Repair or replace. |
Sucking air from intake pipe joint. | Repair or replace. |
Defective fuel injectors. | Replace. |
Defective ECT sensor. | Replace. |
3) The other factors | |
Ignition timing too advanced due to defective timing advance system (ECT sensor, GP switch, CKP sensor and ECM.) | Replace. |
Drive chain is too tight. | Adjust. |
Dirty or heavy exhaust smoke
Too much engine oil in the engine. | Check with inspection window. Drain excess oil |
Worn piston rings or cylinders. | Replace. |
Worn valve guides. | Replace. |
Scored or scuffed cylinder walls. | Replace. |
Worn valves stems. | Replace. |
Defective stem seal. | Replace. |
Worn oil ring side rails. | Replace. |