Skip the auto shop - Our mechanics make house calls

Q: Random misfires

asked by on

About a month ago, I started getting misfires at random times. Since then, it has gotten worse. When the car starts up like normal, every three seconds, it will misfire, and the catalytic converter gets hot - hot enough to turn red. The code reader just gives me "P0300" - random misfire. I have checked the coils, and they were fine. We switched them out anyway, and that didn't help. We tried using three ignition control modules, but there was no change. A new ignition coil went in yesterday, because the old one had a slight burn mark and was arcing. When I changed it, the car ran fine for a second, then went back to misfiring. There is a lot of clear condensation coming from the exhaust, but I don't think it is anything bad like coolant or oil. What could be causing these misfires?

Hello. There are several possibilities that could explain why you are having this problem.

  • One possibility is that you could have one or more faulty fuel injectors, or the fuel injector wiring is damaged.

  • Another possibility is that one or more spark plugs have fouled out.

  • It is also possible that there are bad internal engine parts.

I would suggest that you have a certified technician, like one from YourMechanic, come out and diagnose your car to find out why your engine is misfiring.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Arcing from distributor to valve cover

The coil is the only thing that is putting out high voltage. The ignition spark will always look for the quickest path to ground. This is the way electricity works. If you are getting spark jumping to the ground before...

Q: Found out 1st cylinder in car has no compression....what are my options?

The first thing you have to do is confirm such a diagnosis by getting a second opinion. It is unusual for three cylinders to be perfectly normal and one to have "no" compression. Nevertheless, it is possible. A cylinder...

Q: A/C blows only warm air on driver's side; passenger side is cold

Some A/C systems have problems disconnecting or losing communication between the A/C control head and the temperature blend door actuators. This may require the A/C control head to be reprogrammed by a factory level scanner capable of the reprogramming of...

Related articles

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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
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...