Q: How do I know if I have a bad coil or a bad fuel injector?

asked by on

I had a tune up done and it still runs really rough and bad on gas, the check engine light will blink while misfiring. P0303 cylinder three misfire is the code.

My car has 145000 miles.
My car has an automatic transmission.

The easiest way to test for spark is to pull the spark plug boot off of the number 3 cylinder spark plug and install a spark tester. Most auto parts stores have them for a few bucks. The spark plug boot plugs into the top of the tester, and the other end of the tester has a boot that gets installed onto the spark plug. When the engine is started, there is a section of the tester that actually will light up, or spark, if there is an ignition pulse going to it. As far as the injector goes, you can also purchase what is called a "noid light", that will check to see if the injector in question is getting the electrical signal necessary to fire the injector. You would simply unplug the injector, plug the noid light into the harness for the injector, and when the engine is started, will show a light when the pulse to the injector is present. If this is something that you feel you could use a hand to diagnose and/or repair, contact a certified mechanic, like the mobile mechanics available at YourMechanic.com.

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. How do I know if I have a bad coil or a bad fuel injector?

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: Traction system

It sounds like you may have a faulty wheel speed sensor. The ABS system uses information from your wheel speed sensors to detect if each wheel is rotating at the same speed. If you have different sized tires, a bad...

Q: Hello...I have a 2004 infinity m45. Everytime I started my car it jerked so I took it to a mechanic and I was told my camshaft sensor harness was bad.

Hi there. Anytime the battery is not disconnected and a wiring harness is removed, there is spikes of power that is sent directly to the ECM (computer). Either there is a plug that is not plugged in on your engine...

Q: 08 impala has engine power reduced light on. Car starts

Hello, Unfortunately, this is a common issue in many Impalas. This can happen when the catalytic converter is clogged or has also been known to happen when the traction control system has encountered an error. This light comes on as...

Related articles

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...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.