How to Remove and Replace Your Diesel Engine's Glow Plug

February 27, 2012

If you're having trouble cold starting your diesel engine, the glow plug might need replacement. Learn how to replace the glow plug yourself.

Diesel Engine Maintenance

Diesel engines use a glow plug to pre-warm the air fuel mixture and aid in starting a cold engine. Adding just a little heat to the mixture as it is compressed provides enough impetus in a diesel engine to cause the air fuel mixture to combust. When a glow plug fails, it can distort. When you pull on it, the tip usually breaks off. Here is the easiest method of removing a distorted glow plug without having to remove the cylinder heads from the engine block.

Tools and Materials

  • A compressed air cylinder
  • A shop vac with good suction
  • Wrenches to remove the stuck glow plug
  • Wrenches to remove fuel injectors
  • A socket and wrench to fit the crankshaft bolt
  • A firing order diagram

Bring Engine to Top Dead Center
Find the timing pointer on the engine and rotate the crank with a wrench and socket until the mark on the harmonic dampener and the timing indicator line up. This is top dead center, or TDC, for cylinder number one. Cylinders are paired, so if your engine has a firing order of 12734568, the pairing is one and four, two and five, seven and six and three and eight. Each quarter turn of the crankshaft will bring another cylinder pair to TDC. So, if the glow plug in cylinder number seven is distorted, you'll need to turn the engine 1/2 revolution from the TDC mark on the dampener.

Remove Injector and Loosen Glow Plug
Once you have the affected cylinder at TDC, carefully remove the fuel injector and loosen the glow plug. Apply pressure to remove the glow plug. If you're lucky, it will come out in one piece. Usually the tip will break off. Not to worry. Move ahead to step three.

Apply Air Pressure and Suction
Fashion a small diameter tube to fit over the end of your shop vac hose. Insert this into the fuel injector opening and turn the vacuum on. Have a helper hold the crankshaft so that the air pressure you will apply doesn't end up moving the cylinder down the bore. Squirt some pressurized air into the glow plug opening. This will cause a vortex in the pre-chamber, which will get the broken glow plug tip moving. The suction from the vacuum will draw it out the fuel injector opening.

Carefully replace the fuel injector you removed and make sure the seal is tight. Carefully install a new glow plug and properly tighten it. Reattach the wires to the new glow plug and you're done, unless you have more stuck glow plugs.

This is the easiest and quickest way to remove a stuck glow plug without having to remove the engine cylinder heads.