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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. 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: Is it mechanically safe to coast in neutral?

Technically, least cost operation is attained if engine idling (at stops) does not exceed 60 seconds and, indeed, some studies put the threshold as low as 10 seconds. Certainly 60 seconds is a conservative estimate. This is why "start-stop" features...

Q: Car keeps popping out of first gear.

Hi and thanks for contacting YourMechanic. What is wrong with your vehicle is the transmission shifter detent springs are worn and making the gear shifter not stay locked in. The detent springs are located in the top of the transmission...

Q: Random misfire on cylinder one - 2000 Chevrolet Corvette

Hello. Random misfires can be caused by a few different things. If the coil packs are all good then it may be possible that the issue is not related to the ignition system. A few other things that can cause...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...