Gasoline Engine - Mechanical Trouble Shooting
NOTE:
This is GENERAL
information. This article is not intended to be specific to any unique situation or individual vehicle configuration. The purpose of this Trouble Shooting information is to provide a list of common causes to problem symptoms. For model-specific Trouble Shooting, refer to SUBJECT, DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing.
BASIC GASOLINE ENGINE - MECHANICAL TROUBLE SHOOTING CHART
| CONDITION & POSSIBLE CAUSE | CORRECTION | |
|---|---|---|
| Engine Lopes At Idle | ||
| Intake manifold-to-head leaks | Replace manifold gasket, See ENGINES | |
| Blown head gasket | Replace head gasket, See ENGINES | |
| Worn timing gears, chain or sprocket | Replace gears, chain or sprocket | |
| Worn camshaft lobes | Replace camshaft, See ENGINES | |
| Overheated engine | Check cooling system, See COOLING | |
| Blocked crankcase vent valve | Remove restriction | |
| Leaking EGR valve | Repair leak and/or replace valve | |
| Faulty fuel pump | Replace fuel pump | |
| Engine Has Low Power | ||
| Leaking fuel pump | Repair leak and/or replace fuel pump | |
| Excessive piston-to-bore clearance | Install larger pistons, See ENGINES | |
| Sticking valves or weak valve springs | Check valve train components, See ENGINES | |
| Incorrect valve timing | Reset valve timing, See ENGINES | |
| Worn camshaft lobes | Replace camshaft, See ENGINES | |
| Blown head gasket | Replace head gasket. See ENGINES. | |
| Clutch slipping | Adjust pedal and/or replace components, See ENGINES | |
| Engine overheating | Check cooling system, See COOLING | |
| Auto. Trans. pressure regulator valve faulty | Replace pressure regulator valve | |
| Auto. Trans. fluid level too low | Add fluid as necessary | |
| Improper vacuum diverter valve operation | Replace vacuum diverter valve | |
| Vacuum leaks | Inspect vacuum system and repair as required | |
| Leaking piston rings | Replace piston rings, See ENGINES | |
| Faulty High Speed Operation | ||
| Low fuel pump volume | Replace fuel pump | |
| Leaking valves or worn | Replace valves and/or springs, See ENGINES | |
| Incorrect valve timing | Reset valve timing,See ENGINES | |
| Intake manifold restricted | Remove restriction | |
| Worn distributor shaft | Replace distributor | |
| Faulty Acceleration | ||
| Improper fuel pump stroke | Remove pump and reset pump stroke | |
| Incorrect ignition timing | Reset ignition timing, See TUNE-UP | |
| Leaking valves | Replace valves, See ENGINES | |
| Worn fuel pump diaphragm or piston | Replace diaphragm or piston | |
| Intake Backfire | ||
| Improper ignition timing | Reset ignition timing, See TUNE-UP | |
| Faulty accelerator pump discharge | Replace accelerator pump | |
| Improper choke operation | Check choke and adjust as required | |
| Defective EGR valve | Replace EGR valve | |
| Fuel mixture too lean | Reset air/fuel mixture, See TUNE-UP | |
| Choke valve initial clearance too large | Reset choke valve initial clearance | |
| Exhaust Backfire | ||
| Vacuum leak | Inspect and repair vacuum system | |
| Faulty vacuum diverter valve | Replace vacuum diverter valve | |
| Faulty choke operation | Check choke and adjust as required | |
| Exhaust system leak | repair exhaust system leak | |
| Engine Detonation | ||
| Ignition timing too far advanced | Reset ignition timing, See TUNE-UP | |
| Faulty ignition system | Check ignition timing, See TUNE-UP | |
| Spark plugs loose or faulty | Retighten or replace plugs | |
| Fuel delivery system clogged | Inspect lines, pump and filter for clog | |
| EGR valve inoperative | Replace EGR valve | |
| PCV system inoperative | Inspect and/or replace hoses or valve | |
| Vacuum leaks | Check vacuum system and repair leaks | |
| Excessive combustion chamber deposits | Remove built-up deposits | |
| Leaking, sticking or broken valves | Inspect and/or replace valves | |
| External Oil Leakage | ||
| Fuel pump improperly seated or worn gasket | Remove pump, replace gasket and seat properly | |
| Oil pan gasket broken or pan bent | Straighten pan and replace gasket | |
| Timing chain cover gasket broken | Replace timing chain cover gasket | |
| Rear main oil seal worn | Replace rear main oil seal | |
| Oil pan drain plug not seated properly | Remove and reinstall drain plug | |
| Camshaft bearing drain hole blocked | Remove restriction | |
| Oil pressure sending switch leaking | Remove and reinstall sending switch | |
| Excessive Oil Consumption | ||
| Worn valve stems or guides | Replace stems or guides, See ENGINES | |
| Valve "O" ring seals damaged | Replace "O" ring seals, See ENGINES | |
| Plugged oil drain back holes | Remove restrictions | |
| Improper PCV valve operation | Replace PCV valve | |
| Engine oil level too high | Remove excess oil | |
| Engine oil too thin | Replace thicker oil | |
| Valve stem oil deflectors damaged | Replace oil deflectors | |
| Incorrect piston rings | Replace piston rings, See ENGINES | |
| Piston ring gaps not staggered | Reinstall piston rings, See ENGINES | |
| Insufficient piston ring tension | Replace rings, See ENGINES | |
| Piston ring grooves or oil return | slots clogged Replace piston rings, See ENGINES | |
| Piston rings sticking in grooves | Replace piston rings, See ENGINES | |
| Piston ring grooves excessively worn | Replace piston and rings, See ENGINES | |
| Compression rings installed upside down | Replace compression rings correctly, See ENGINES | |
| Worn or scored cylinder walls | Rebore cylinders or replace block | |
| Mismatched oil ring expander and rail | Replace oil ring expander and rail, See ENGINES | |
| Intake gasket dowels too long | Replace intake gasket dowels | |
| Excessive main or connecting rod bearing clearance | Replace main or connecting rod bearings, See ENGINES | |
| No Oil Pressure | ||
| Low oil level | Add oil to proper level | |
| Oil pressure sender or gauge broken | Replace sender or gauge | |
| Oil pump malfunction | Remove and overhaul oil pump, See ENGINES | |
| Oil pressure relief valve sticking | Remove and reinstall valve | |
| Oil pump passages blocked | Overhaul oil pump, See ENGINES | |
| Oil pickup screen or tube blocked | Remove restriction | |
| Loose oil inlet tube | Tighten oil inlet tube | |
| Loose camshaft bearings | Replace camshaft bearings, See ENGINES | |
| Internal leakage at oil passages | Replace block or cylinder head | |
| Low Oil Pressure | ||
| Low engine oil level | Add oil to proper level | |
| Engine oil too thin | Remove and replace with thicker oil | |
| Excessive oil pump clearance | Reduce oil pump clearance, See ENGINES | |
| Oil pickup tube or screen blocked | Remove restrictions | |
| Main, rod or cam bearing clearance excessive | Replace bearing to reduce clearance, See ENGINES | |
| High Oil Pressure | ||
| Improper grade of oil | Replace with proper oil | |
| Oil pressure relief valve stuck closed | Eliminate binding | |
| Oil pressure sender or gauge faulty | Replace sender or gauge | |
| Noisy Main Bearings | ||
| Inadequate oil supply | Check oil delivery to main bearings | |
| Excessive main bearing clearance | Replace main bearings, See ENGINES | |
| Excessive crankshaft end play | Replace crankshaft, See ENGINES | |
| Loose flywheel or torque converter | Tighten attaching bolts | |
| Loose or damaged vibration damper | Tighten or replace vibration damper | |
| Crankshaft journals out-of-round | Re-grind crankshaft journals | |
| Excessive belt tension | Loosen belt tension | |
| Noisy Connecting Rods | ||
| Excessive bearing clearance or missing bearing | Replace bearing, See ENGINES | |
| Crankshaft rod journal out-of-round | Re-grind crankshaft journal | |
| Misaligned connecting rod or cap | Remove rod or cap and realign | |
| Incorrectly tightened rod bolts | Remove and re-tighten rod bolts | |
| Noisy Pistons and Rings | ||
| Excessive piston-to-bore clearance | Install larger pistons, See ENGINES | |
| Bore tapered or out-of-round | Rebore block | |
| Piston ring broken | Replace piston rings, See ENGINES | |
| Piston pin loose or seized | Replace piston pin, See ENGINES | |
| Connecting rods misaligned | Realign connecting rods | |
| Ring side clearance too loose or tight | Replace with larger or smaller rings | |
| Carbon build-up on piston | Remove carbon | |
| Noisy Valve Train | ||
| Worn or bent push rods | Replace push rods, See ENGINES | |
| Worn rocker arms or bridged pivots | Replace push rods, See ENGINES | |
| Dirt or chips in valve lifters | Remove lifters and remove dirt/chips | |
| Excessive valve lifter leak-down | Replace valve lifters, See ENGINES | |
| Valve lifter face worn | Replace valve lifters, See ENGINES | |
| Broken or cocked valve springs | Replace or reposition springs | |
| Too much valve stem-to-guide clearance | Replace valve guides, See ENGINES | |
| Valve bent | Replace valve, See ENGINES | |
| Loose rocker arms | Retighten rocker arms, See ENGINES | |
| Excessive valve seat run-out | Reface valve seats, See ENGINES | |
| Missing valve lock | Install new valve lock | |
| Excessively worn camshaft lobes | Replace camshaft, See ENGINES | |
| Plugged valve lifter oil holes | Eliminate restriction or replace lifter | |
| Faulty valve lifter check ball | Replace lifter check ball, See ENGINES | |
| Rocker arm nut installed upside down | Remove and reinstall correctly | |
| Valve lifter incorrect for engine | Remove and replace valve lifters | |
| Faulty push rod seat or lifter plunger | Replace plunger or push rod | |
| Noisy Valves | ||
| Improper valve lash | Re-adjust valve lash, See ENGINES | |
| Worn or dirty valve lifters | Clean and/or replace lifters | |
| Worn valve guides | Replace valve guides, See ENGINES | |
| Excessive valve seat or face run-out | Reface seats or valve face | |
| Worn camshaft lobes | Replace camshaft, See ENGINES | |
| Loose rocker arm studs | Re-tighten rocker arm studs, See ENGINES | |
| Bent push rods | Replace push rods, See ENGINES | |
| Broken valve springs | Replace valve springs, See ENGINES | |
| Burned,Sticking or Broken Valves | ||
| Weak valve springs or warped valves | Replace valves and/or springs, See ENGINES | |
| Improper lifter clearance | Re-adjust clearance or replace lifters | |
| Worn guides or improper guide clearance | Replace valve guides, See ENGINES | |
| Out-of-round valve seats or improper seat width | Re-grind valve seats | |
| Gum deposits on valve stems, seats or guide | Remove deposits | |
| Improper spark timing | Re-adjust spark timing | |
| Broken Pistons/Rings | ||
| Undersize pistons | Replace with larger pistons, See ENGINES | |
| Wrong piston rings | Replace with correct rings, See ENGINES | |
| Out-of-round cylinder bore | Re-bore cylinder bore | |
| Improper connecting rod alignment | Remove and realign connecting rods | |
| Excessively worn ring grooves | Replace pistons, See ENGINES | |
| Improperly assembled piston pins | Re-assemble pin-to-piston, See ENGINES | |
| Insufficient ring gap clearance | Install new rings, See ENGINES | |
| Engine overheating | Check cooling system | |
| Incorrect ignition timing | Re-adjust ignition timing, See TUNE-UP | |
| Excessive Exhaust Noise | ||
| Leaks at manifold to head, or to pipe | Replace manifold or pipe gasket | |
| Exhaust manifold cracked or broken | Replace exhaust manifold, See ENGINES | |