Symptoms of Bad or Failing Glow Plugs

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Glow plugs are an engine management component that is found on vehicles equipped with diesel engines. Their purpose is to preheat, and help warm up the engine’s cylinders so that diesel combustion can occur more easily. They play an especially important part in warming the vehicle’s cylinders during cold starts, where starting the engine is most difficult. Glow plugs use an electrode which will warm up and glow orange when current is applied. When the glow plugs have an issue, they can usually cause problems with the driveability of the vehicle. Usually bad or failing glow plugs will produce a few symptoms that can alert the driver of a potential issue.

1. Engine misfires or decrease in power and acceleration

Engine misfires are one of the first symptoms of an issue with the vehicle’s glow plugs. If the glow plugs malfunction they will not provide the additional heat that aids in diesel combustion, which may cause the engine to experience misfires. The misfires may cause a loss in power, acceleration, and even fuel efficiency.

2. Hard starting

Another symptom of an issue with the vehicle’s glow plugs is hard starting. Unlike gasoline engines, which use a spark to ignite the fuel mixture, diesel engines rely solely on cylinder pressures to ignite the diesel fuel mixture. If the glow plugs fail, the engine will have to overcome additional pressure in order to ignite the mixture, which may result in hard starting.

3. Black smoke from the exhaust

Another symptom of an issue with the glow plugs is black smoke from the exhaust. Faulty glow plugs may disturb the sensitive diesel combustion process, which may cause the engine to produce black smoke from the tailpipe. Black smoke can also be caused by a wide variety of other issues, so having the engine properly diagnosed is highly recommended.

Glow plugs are found on virtually all diesel engines, and play an important role in starting and operating the engine. If your vehicle is displaying any of the symptoms above, or you suspect that your glow plugs may be having an issue, have the vehicle inspected by a professional technician, such as one from yourMechanic, to determine if the glow plugs need to be replaced.


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Number of Reviews

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Travis

12 years of experience
344 reviews
Travis
12 years of experience
Oldsmobile Alero - Engine is misfiring - Saint Paul, Minnesota
Travis allowed me to watch the trouble-shooting and resolve of my Alero. He was totally honest, forthright, and completed the repair within two hours. Travis was my second estimate and, comparatively speaking, wins the medal of honor! Thank you, Travis!
Ford E-350 Super Duty - Engine is misfiring Inspection - Saint Paul, Minnesota
Travis was a great diagnostician and also wise enough to know when not to do something he wasn't equipped for. I feel better talking to my regular mechanic now that I know what the problem is and how much I can expect it to cost. Will call Travis again when the need arises!

Duane

24 years of experience
387 reviews
Duane
24 years of experience
Cadillac SRX - Engine is misfiring - Poway, California
I thought my caddy was gonna be a big expensive problem for me. And then came DUANE. Not only was it a small problem but it was also not expensive. DUANE took care of the problem in his usual professional way. Words can't explain how happy i am.
Jaguar XF - Engine is misfiring - Fallbrook, California
Duane provided me with excellent service! He is clearly an experienced professional! His knowledge, experience, and pride in his work are clearly reflected in the quality of his work. He will be the only mechanic I request going forward. I am greatly satisfied with the service he provided me with and

Joe

14 years of experience
365 reviews
Joe
14 years of experience
Mercury Mariner - Engine is misfiring - Franklin, Tennessee
He was very thorough and informative. Joe takes the time to show me what’s going on with my cars and what to look for down the road. I’ve used Joe several times and he is great!
Toyota Avalon - Engine is misfiring - Nashville, Tennessee
Joe is very professional! Explained all my options to me in a way that I could understand them to my satisfaction! Joe even went above and beyond to give me exceptional customer service that meet my personal needs by explaining the different areas in the engine that might need further attention if the sensor did not do the job! Fortunately the sensor has been perfect , no more check engine light!

Walter

45 years of experience
85 reviews
Walter
45 years of experience
Nissan Sentra - Engine is misfiring - Tulsa, Oklahoma
Very helpful and knowledgeable. Appreciate the friendliness on top of it, would definitely recommend.

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