Q: The vehicle is jerking and not firing and the plug number 4 is soaked with oil.

asked by on January 16, 2017

I started my car last weekend and drove it. After, about 5 minutes, it started jerking very badly and it wasn't firing. There was no fault indication on the screen. I have run a diagnostic test and it didn't reveal anything. My mechanic checked the plugs and discovered that the plug number 4 is soaked in oil. The vehicle is still jerking and that plug is still oil soaked. Even when we replaced the plug, it still had the same problem.

My car has 19000 miles.
My car has an automatic transmission.

Hi there. When a spark plug has excessive oil on the plug, then there is excessive oil getting into the cylinder. This will foul out the spark plug and cause a misfire. The misfire is causing the engine to be jerky. There are three areas that cause excessive oil in the cylinder.

  • The oil scraper rings on the piston is worn and causing the oil to not crape down off the cylinder wall.
  • The Positive Crankcase Ventilation Valve (PCV) is plugged up causing the crankcase to over pressurize forcing the oil into the cylinder.
  • The valve guide seal on the intake valve is split or damaged causing oil to puddle up on the intake valve and being sucked in on the intake stroke.

Check the above areas and one of them will be the cause and repair to your symptom. If you need further assistance with your engine having excessive oil on the spark plugs, then seek out a professional, such as one from Your Mechanic, to help you.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Input turbine speed sensor B has stopped working

Hello and thank you for your question. It sounds like the input turbine speed sensor B has failed or lost connection to the engine control module (ECM). You will first need to check the wiring to the sensor and see...

Engine ran out of oil

Depending on the severity of the damage done to the engine as a result of not having oil, you may not have many other options. When an engine is run out of oil, there are many different things that can...

Wrong antifreeze and fuel additive used and the car is noisy and runs roughly

This vehicle should not be run any at all until it can be diagnosed and repaired. In cases where coolant has been put into the engine, this can damage various engine components such as the bearings, pistons and crankshaft....

Related articles

How Often Do Spark Plug Wires Need to Be Changed?
Spark plugs provide the electricity necessary for combustion to happen by igniting atomized fuel in an engine's cylinders. However, they need a...
How to Get Mercedes-Benz Dealership Certified
Mercedes Benz dealerships offer automotive technician jobs to those certified through Mercedes-Benz's Automotive Systems Technical & ELITE programs.
A Buyer’s Guide to the 2012 Mercedes-Benz G-Class
Combining Combining rugged performance with an iconic boxy exterior style, the 2012 Mercedes-Benz G-Class is a hallmark of the SUV segment. It manages to combine true off-road capabilities with luxurious comfort and outstanding on-road performance in a way that most...