bmwrepairs: how to inspect spark plugs

Spark Plugs

Inspection

Inspect the spark plug for the following:

Deposit build-up that is closing the gap between the electrodes. Deposits are caused by oil or carbon fouling. Clean the spark plug..
Check for wet, black deposits on the insulator shell bore electrodes, caused by excessive oil entering the combustion chamber through worn rings and pistons, excessive valve-to-guide clearance or worn or loose bearings. Correct the oil leak concern. Install a new spark plug.
Look for black, dry, fluffy carbon deposits on the insulator tips, exposed shell surfaces and electrodes, caused by a spark plug with an incorrect heat range, dirty air cleaner, too rich a fuel mixture or excessive idling. Install new spark plugs.
Normal burning.
Light tan or gray deposits on the firing tip.
Pre-ignition. This identified by melted electrodes and a possibly damaged insulator. Metallic deposits on the insulator indicate engine damage. This may be caused by incorrect ignition timing, wrong type of fuel or the unauthorized installation of a heli-coil insert in place of the spark plug threads. Install a new spark plug.
Overheating. This is identified by a white or light gray spots and with bluish-burnt appearance of electrodes. This is caused by engine overheating, wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel pump pressure or incorrect ignition timing. Install a new spark plug.
Fused deposits. These are identified by melted or spotty deposits resembling bubbles or blisters. These are caused by sudden acceleration. Install a new spark plug.

Inspection & Gapping

Check the plugs for deposits and wear. Look carefully at the center electrode protrudes through the center of the porcelain. If the center electrode is eroded or rounded, replace the spark plugs. If the plugs are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug-cleaning machine, which are sometimes found in service stations. These machines do a good job of cleaning the spark plug, although they tend to remove the protective anti-corrosive coating on the spark plug threads. They also cause the surface of porcelain around the center electrode to become slightly porous, allowing deposits to bond more easily to the porcelain. If a plug cleaner is used to clean the plugs, be sure the plug is thoroughly cleaned. The abrasive material used in the spark plug cleaners is very hard, and if allowed to enter the engine's combustion chamber, could cause internal damage. An acceptable job of cleaning the spark plug can be accomplished by using a stiff wire brush. Once the plugs are cleaned, the spark plug gap must be checked and reset to specification.

WARNING

If the original equipment spark plugs are platinum tip spark plugs, or have more than one electrode, the plug gap must not be adjusted.

Always check the spark plug gap before installation. Using a suitable spark plug gap gauge, check the spark plug gap. Make sure the L-shaped electrode connected to the body of the spark plug is parallel to the center electrode. If necessary, adjust the L-shaped electrode to attain the correct gap and proper alignment. Make sure to use the specified size wire gauge, which must pass between the electrodes with a slight drag; the next larger size should not be able to pass, while the next smaller size should pass freely. When adjusting a spark plug gap, always set the gap to the minimum specification to allow for electrode wear.

Always check the gap on new plugs as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap because the reading may be inaccurate. A round-wire type gapping tool is the best tool for checking the plug gap. The correct gauge should pass through the electrode gap with a slight drag. If in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use this to adjust the side electrode until the proper clearance is obtained. Never attempt to bend the center electrode. Be careful not to bend the side electrode too far or too often as it may weaken and break off inside the engine, requiring removal of the cylinder head to retrieve it.

The recommended plug gap for original equipment spark plugs for spark plugs where gapping is permitted is as follows:

M3 models: 0.024-0.028 inches (0.6-0.7mm)

E30 and E36 models (except M3 and multiple electrode spark plugs): 0.028-0.032 inches (0.7-0.8mm)

Multiple electrode spark plugs: 0.032-0.035 inches (0.9-1.0mm)

NOTE

Multiple electrode spark plugs with three or four electrodes can be checked, but should not be adjusted.

Fig. Inspect the spark plug to determine engine running conditions

Fig. A variety of tools and gauges are needed for spark plug service

Fig. Checking the spark plug gap with a feeler gauge

Fig. Adjusting the spark plug gap

Fig. If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs

Removal & Installation

Before servicing the vehicle, refer to the Precautions section.

Switch off ignition.

Disconnect the negative battery cable.

If equipped, removal engine cover.

Remove ignition coils.

Unscrew spark plugs with special tool 12 1 171.

To install, reverse removal procedure. Tighten spark plugs to 18 ft. lbs. (24 Nm).

Spark Plug Heat Range

The spark plug heat range is the ability of the plug to dissipate heat. The deeper the insulator recedes into the body of the spark plug, the more heat the spark plug will retain and the hotter the plug will operate. If the amount the insulator recedes into the body of the spark plug is decreased, the less the plug will retain heat, and the cooler it will operate. A plug that absorbs little heat and remains too cool will quickly accumulate deposits of oil and carbon since it is not hot enough to burn them off. This causes carbon to build up on the porcelain insulator and the center electrode, creating an alternate path for the high energy electrical spark which eventually leads to spark plug fouling and consequently to misfiring.

A spark plug that absorbs too much heat will burn off deposits, however, due to the increased combustion temperature, the electrodes may also burn away more quickly and the excessive heat may cause pre-ignition or internal engine damage. Pre-ignition, also referred to as detonation, takes place when the combustion chamber gets hot enough to ignite the air/fuel mixture before the actual spark occurs. This early ignition may cause a "pinging", knocking or rattling noise during low speed acceleration or when operated under a heavy load condition, such as climbing a steep hill. Note that detonation can occur without being heard.

On engines equipped with Knock Sensors (KS), the Engine Control Module (ECM) will retard the ignition timing to prevent internal engine damage when detonation is detected. This will allow the engine to operate safely, however performance will be compromised.

Fig. Spark plug heat range

The general rule of thumb for choosing the correct heat range when selecting a spark plug is: consult the vehicle's owner's manual or a spark plug manufacturer's supply catalog for recommendations. If only one heat range of spark plug is listed, use the recommended plug, and note the recommended spark plug gap. If more than one heat range of spark plug is listed, depending on operating conditions, evaluate the type of driving the vehicle is most often subjected to. If the vehicle is used for extended high speed, long distance travel for long periods of time, in warm weather, use the colder plug of the recommend spark plugs. If, however, most of the driving is stop and go, or the vehicle is operated in extremely cold climates, use the hotter of the recommended spark plugs. Usually, original equipment plugs are a good compromise between the 2 styles of driving, and most vehicles rarely need to have their plugs differ from the factory-recommended heat range.

-------------

Also go through this link below for more spark plug details:---

How to test and replace Spark Plug wires on 2005 BMW 325?

http://bmwrepairhelp.blogspot.com/2011/11/how-to-test-and-replace-spark-plug.html

---------

This all will help you to understand your spark plugs working and confirming the spark plug problem.

---------

For more car related problem troubleshooting:---

This are the sections, you can go through and click the link to read its troubleshooting.

---------

The car will not start?

http://schematicsdiagram.blogspot.com/2011/06/car-will-not-start.html

-----------------

Car will not crank?

http://schematicsdiagram.blogspot.com/2011/06/car-will-not-crank.html

-----------

Car has no spark?

http://schematicsdiagram.blogspot.com/2011/06/car-has-no-spark.html

-------------

How to troubleshoot car battery?

http://schematicsdiagram.blogspot.com/2011/06/how-to-troubleshoot-car-battery.html

-----------------

How to test starter solenoid?

http://schematicsdiagram.blogspot.com/2011/06/how-to-test-starter-solenoid.html

--------------------

How to test cars starter?

http://schematicsdiagram.blogspot.com/2011/06/how-to-test-cars-starter.html

How to replace starter in car?

http://schematicsdiagram.blogspot.com/2011/06/how-to-replace-starter-in-car.html

-----------

car will turn over but will not start?

http://technoanswers.blogspot.com/2011/05/car-will-turn-over-but-will-not-start.html

-----------------

Car wont start?

http://howtobyme.blogspot.com/2011/10/car-wont-start.html

----------

Diagnosis & Testing

Prior to diagnosis or testing procedures, visually inspect the components of the ignition and engine control systems. Check for the following:

Blown fuses

Poor spark plug connections

Damaged or corroded ignition wires

Damaged or worn electrical insulation

Discharged battery or low alternator output

Ignition module multi-connector condition

Damaged, corroded, or loose electrical connections

Excessively worn, defective, or damaged spark plugs

Excessively worn or damaged distributor cap or rotor

Check the spark plug wires and boots for signs of poor insulation that could cause shorting or crossfiring. Make sure the battery is fully charged and that all accessories are off during diagnosis and testing. Make sure the idle speed is within specification. Check all of the fuel injector electrical connections.

Secondary Spark Test

WARNING

When testing the ignition system for a high-energy spark, make sure the test equipment is sufficiently grounded. Failure to do so may cause severe and expensive internal component damage. When testing for an ignition, spark make sure the area is free of any flammable materials. Do not hold or place hands or fingers near the test equipment when checking for a high voltage spark.

Fig. This spark tester has an adjustable air-gap for measuring spark strength and testing different voltage ignition systems

Fig. To test for spark at the plug, ground the body to a known good ground such as this ground strap bolt

Checking for a high-energy spark is easily performed using a spark tester (available at most automotive parts stores). Three types of spark testers are commonly available:

The Neon Bulb type: This tool connects to the spark plug wire and flashes with each ignition pulse. This is easy to use as it lights up with each ignition pulse

The Air Gap type: This tester is adjusted according to the spark plug gap specification for the engine. It is very useful because the gap can be adjusted to check the strength of the electrical spark and the color of the spark can be verified

The Spark Plug simulator: This looks like a spark plug, and has a grounding alligator style clip on the side. This checker is easy to use, and the spark color can be monitored

The last two types of testers mentioned allow the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong). To use these testers proceed as follows:

Disconnect a spark plug wire from the spark plug end.

Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.

Crank the engine and check for spark at the tester.

If spark exists at the tester, the ignition system is functioning properly.

If all of the spark tests for all of the spark plug wires indicate irregular or weak spark, perform the following:
1. Refer to the coil test.
2. Carefully inspect the distributor cap and rotor for damage, corrosion or excessive wear.
3. Inspect and test the ignition wires. Check the resistance of each spark plug wire. Refer to Section 1 for checking the resistance of the spark plug wires. If the wires are within specification, it will be necessary to diagnose the individual components of the ignition system.

If one or more, but not all of the tests indicate irregular, or weak spark;
1. Inspect and test the ignition wires. Check the resistance of each spark plug wire. Refer to Section 1 for checking the resistance of the spark plug wires. If the wire is within specification, it will be necessary to diagnose the individual components of the ignition system.
2. Carefully inspect the distributor cap and rotor for an internal short, damage, corrosion or excessive wear.

If spark does not exist, perform the following:

Remove the distributor cap, detach all of the electrical connectors at the distributor, and ensure that the rotor is turning when the engine is cranked.

Carefully inspect the distributor cap and rotor for damage, corrosion or excessive wear.

Inspect and test the ignition wires. Check the resistance of each spark plug wire. Refer to Section 1 for checking the resistance of the spark plug wires. If the wire is within specification, it will be necessary to diagnose the individual components of the ignition system.

-------

For more car related problem troubleshooting:---

This are the sections, you can go through and click the link to read its troubleshooting.

---------