Skip the auto shop - Our mechanics make house calls

Q: After installing new spark plugs they soot up after 70 miles

asked by on

Car starts missing and stalls after driving and plugs foul

My car has 400000 miles.
My car has an automatic transmission.

High mileage engines leak oil into the combustion chamber through worn out valve stem oil seals, worn valve guides and ill fitting piston rings. If a substantial amount of oil is entering the combustion chamber the plugs will quickly foul. You might also have leaking fuel injectors and/or the air fuel ratio is off allowing excess raw gas into the combustion chamber. That overly rich running condition will foul the plugs as well. These are the more common causes.

There are other possibilities but a mechanic should do a thorough check of the engine to see if perhaps changing the valve stem seals and correcting any operating condition (e.g., too rich) might make the engine usable for a while longer. If the 400,000 miles is on the present engine, it might be necessary to rebuild it to fully resolve the plug fouling issue.

If you plan on getting this repaired, consider YourMechanic as one of our mobile technicians can come to your home to diagnose the misfiring firsthand and help you make the necessary repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
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

Q: Idling high - 1993 Saab 9000

The Idle Air Control valve and turbo-bypass valve in your model are common suspects for vehicle stalling as you describe. A professional mechanic, like Your Mechanic, can diagnose and repair this problem including replacing the valves.

Q: How do I put a USB device in shuffle mode?

When playing a USB device through the sound system, you can shuffle in two ways: Folder random (shuffles within the chosen folder), or all folders random (shuffles all of the available tracks). To set the device in shuffle mode, press...

Q: Idle Problem & Exhaust sputtering noises

With the information that you have provided, I would surmise that you are describing the signs of an engine misfire. Pulling the diagnostic codes with a code reader will probably show codes that relate to a misfire, and could help...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...