Skip the auto shop - Our mechanics make house calls

Q: Misfire on cylinder 8

asked by on

I use premium gas. When I start my vehicle, it is fine, but after about 5 minutes of driving it is just not running right, it goes from smooth to rough. The misfire diagnostic came from a code reader a friend of mine owns. I had a complete oil change, a full service done only a couple of days ago, so all is good on that front. Puzzled.

My car has 144000 miles.
My car has an automatic transmission.

Misfires are caused by lack of fuel or the ignition system isn’t providing the needed spark. At least these are the most common single cylinder failures. It is possible, all be it remotely, that you have a compression problem, but this would reveal itself when cold as well. Compression problems don’t come and go.

The good news is you know which cylinder the problem is at. My first question to you is, how many miles ago were your spark plugs replaced? Most cars don’t go beyond 60,000 miles. Some do, but this only means you will experience a failure with a spark plug instead of replacing them before they fail. Without knowing what was done with your full service, this very’s quite a bit based on many factors, I cannot say for certain what to do next. If your ignition system was serviced along with your full service, I would take the car back to who did the work. This will likely fall under a warranty issue with them.

Injectors can fail and clog. If you have an injector problem in cylinder number eight, it can be cleaned with the appropriate injection cleaning machine. The machines work much better than dumping something into the fuel tank. The injector is an electric component that under goes much stress. It may have electrically failed.

A thorough diagnostic test should be performed by a qualified technician. I recommend the following service from YourMechanic; engine is misfiring inspection which can be performed by an expert at your home or office.

Good luck!

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: Flames coming from the tailpipe and rough idle

Hello there, many common faults will cause your 1984 Dodge D250 to have a rough engine idle and have flames coming from the exhaust. When flames are seen coming form the exhaust it is most often due to unburnt fuel...

Q: I got a2002 jag stype how do i put tranny fluid in

The fill plug is on the side of the tail shaft. You need to pull out the center plug on the drain plug and fill through the fill hole until the fluid comes out of center of drain plug. ...

Q: Misfiring car won't start 2002 Honda Accord

Hi! When a vehicle's engine will crank over at normal speed but won't start, it is lacking fuel or ignition spark. The test that is performed to check for correct fuel pressure involves attaching a gauge to the fuel rail...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.