EXPERTEC TSB (01-95-36)

Publication date: 1995-01-01
Reference number: 01-95-36

EXPERTEC TSB

TECHNICAL SERVICE BULLETIN

Reference Number(s): 01-95-36, Date of Issue: 01/01/95

SPARK PLUG DIAGNOSIS - OLDSMOBILE MODELS - (ENGINE MECHANICAL)

Model(s): All Oldsmobile Models

Bulletin No.: Oldsmobile 01-95-36

Date: 01/01/1995

SERVICE INFORMATION

Engine control technology has changed tremendously over the last decade. With the advent of fuel injection and computer controlled ignition systems, it has been much easier to control engine performance and emission.

Despite the improvements to engine controls, engine basic principles remain the same and so have some of the problems associated with them. We still use spark plugs, engine lubrication and fuel delivery systems that, if not working properly, can create undesirable spark plug deposits, ignition firing problems and even engine failure.

WHAT DEPOSITS LOOK LIKE

The following chart gives an idea of what deposits look like and the causes of spark plug failure.

NORMAL OPERATION

Brown to grayish-tan deposits and slight electrode wear indicates correct spark plug heat range. A small amount of red-brown, yellow, and white powdery material may also be present on the insulator tip around the electrode. These deposits are normal combustion by-products of fuels and lubricating oils with additives.

CARBON FOULED (SOOTED)

Dry, fluffy black carbon (soot) deposits due to overrich carburetion, sticky EFE (Early Fuel Evaporation) valve, a faulty automatic choke, a sticking manifold heat valve, leaking fuel injectors, or excessive fuel pressure in fuel injection system. A clogged air cleaner can restrict air flow to the carburetor causing rich mixtures. Poor ignition output caused by weak coil(s) or worn ignition wires can reduce output voltage and cause misfiring.

Excessive idling or slow speeds under light loads can keep spark plug temperatures so low that normal combustion deposits may not burn off.

OIL FOULED

Wet, Oily Deposits with minor electrode wear may be caused by oil pumping past worn rings. "Break-in" of a new or recently overhauled engine before rings are fully seated may also result in this condition.

DEPOSIT FOULING "A"

Red, brown, yellow and white colored coatings on the insulator tip. These coatings are by-products of combustion and come from the fuel and lubricating oil, both of which may contain additives. Most powdery deposits have no adverse effect on spark plug operation; however, they may cause intermittent missing under severe operating conditions, especially at high speeds and under heavy loads.

DEPOSIT FOULING "B"

Deposits are similar to those identified as Deposit Fouling "A". These coatings are by-products of combustion and come from the fuel and lubricating oil. Excessive valve stem clearance and/or defective intake valve seals will allow excessive lube oil to enter the combustion chamber with the fuel. The deposits will accumulate on the portion of the spark plug projecting into the chamber and will be heaviest on the side facing the intake valve. Defective seals should be suspected when the condition is found in only one or two cylinders.

DEPOSIT FOULING "C"

Most powdery deposits, as shown in "A", have no adverse effect on the operation of the spark plug as long as they remain in the powdery state. However, under certain conditions, these deposits melt and form a shiny glaze on the insulator which, when hot, acts as a good electrical conductor. This allows the current to follow the deposit instead of jumping the gap, thus shorting out the spark plug.

DETONATION

Overadvanced ignition timing, or the use of low octane fuel, will result in detonation, commonly referred to as engine knock or "ping." This causes severe shock inside the combustion chamber, resulting in damage to the adjacent parts, which include the spark plugs. A common result of prolonged detonation is to have the side wire of the spark plug torn off.

PRE-IGNITION

Causes burned or blistered insulator tips and badly eroded electrodes. Excessive overheating is indicated. Cooling system restrictions, sticking valves, or over-lean-air-fuel mixtures are common causes of preignition. Incorrect spark plugs (too high a heat range), or improper installation are also possible causes. Sustained highspeeds or a heavy load can produce high temperatures which cause preignition.

HEAT SHOCK FAILURE

This is a common cause of broken and cracked insulator tips. Over-advanced ignition timing and low grade fuel are usually responsible for heat shock failure. Rapid increase in tip temperature under severe operating conditions causes heat shock and fracture results. Another common cause of chipped or broken insulator tips is carelessness in regapping by either bending the center wire to adjust the gap, or allowing the gapping tool to exert pressure against the tip of the center electrode or insulator when bending the side electrode to adjust the gap.

INSUFFICIENT INSTALLATION TORQUE

Poor contact between the spark plug and the engine seat will cause the condition shown in the picture. The lack of proper heat transfer, resulting from poor seat contact, causes excessive overheating of the spark plug and, in many cases, severe damage as shown. Dirty threads in an engine head can also result in the plug seizing before it is seated.

THREAD SEIZURE

Scale and deposit-filled threads will not allow proper compression for seating.

CAUTION: Recommended installation torque may be attained without compressing the engine seat gasket for applications requiring a gasket seat spark plug. For taper seat spark plug applications, recommended installation torque may be attained without taper-seat engagement in the cylinder head. Operation of an engine with this type of installation can result in plug overheating and destruction of the engine or spark plug, or both.

Always ensure that cylinder head and spark plug threads are free of deposits, burrs and scale. When necessary, "chase" the engine threads with a thread cleaning tool.