Skip the auto shop - Our mechanics make house calls

Q: My car has a misfire, poor acceleration, and poor fuel burn (all the coils are good)

asked by on

Bad missfire bad excelaration ruff idle and bad fuel economy. All the coils are good but have a code flashing then stop and start flashing again

My car has 217000 miles.
My car has an automatic transmission.

Hello and thanks for your question. Check the condition of the spark plugs to see if they are fouled out. If the spark plugs are in good shape, then unplug one injector at a time from the harness while the engine is running. Listen for the engine to run more rough than it already does. If there is no change when unplugging an injector harness to an injector, then that injector is not working.

If all of the injectors are working correctly, then you would need to perform a compression test to see if any of the rings are sealed inside the engine. The first puff on the gauge to the compression tester should be at least 1/2 of the max pressure produced. If the pressure is less than 1/2, then the rings are not sealing. If the pressure is 1/2 the max pressure on the first puff, then the rings are in good shape. Then you would need to perform a leak down test to determine if the valve train on the engine is not burned.

If you cannot determine the source of the misfire, then seek out a professional, preferably a YourMechanic certified technician who can assist you with your vehicle at your home or office.

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!
  • Home
  • Questions
  • My car has a misfire, poor acceleration, and poor fuel burn (all the coils are good)

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: How do I check the fuel economy on my car?

There are several ways to determine the actual fuel economy you’re getting from your Accord, but Honda actually states that the best option is “direct calculation”. That means you’re going to have to use math. Don’t worry, though. It’s really...

Q: Car loses power and stalls - 2014 Cadillac ATS

Hi! You may have to leave your vehicle with the dealership in order for them to be able to duplicate the concern. While it is not necessary for there to be diagnostic trouble codes present in the vehicle's computer in...

Q: Cylinder 3 misfires.

Hi there. From the description you have provided, a lot has been done to overcome your vehicle's engine misfire issue. Due to the many possibilities, that can cause a cylinder misfire (ie; spark plug, ignition coil, fuel injector, vacuum leak,...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...
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...