Q: Cylinder #4 misfire, PO304

asked by on

Hello, My vehicle is mainly repaired by me. I take pride in the repairing and maintenance of my vehicles. But the repair is a bit out of my league this time. My truck is on idle stuttering and almost shutting off. The exhaust is spitting out light smoke and gas. It smells like its burning rich. I have replaced the spark plug and the wire on that cylinder and checked the coil and its all good. The only thing remaining is the injector on that cylinder. I figure its stuck and dripping constant fuel into the cylinder? The vehicle is parked at home now. I cannot drive it this way. My question is, from my description, would it be the injector #4?

My car has 180000 miles.
My car has an automatic transmission.

In order to know for sure that your problem is with the injector for the number 4 cylinder, is to do a fuel pressure leak down. If the fuel pressure does not leak down after you turn on the key and the pressure rises, then let it sit. The fuel pressure should stay up and not bleed down more than one PSI per 15 minutes max. If you see the pressure go down pretty fast then your injector may be the reason why. You would have to block off the return line on the fuel rail if it has one, to make sure that it’s not the fuel pressure regulator doing the leaking.

If the injector is the suspect, replacing it will be the answer. If you do not have any pressure loss, you will need to do an injector driver test for the cylinder by hooking up a noid tester light to the injector connector and see if the light blinks while the engine is running. If the light stays on, then the engine control module has a shorted injector driver. If the light blinks then you know the injector circuit is okay. Afterwards, a compression test on the cylinder is necessary. You will most likely find out that the injector is leaking and flooding the cylinder out. Make sure to check the oil to make sure that it’s not getting over filled by fuel leaking into the cylinder. If you feel you need help diagnosing the problem then contact a qualified mechanic to assess your misfire and make the necessary repairs to get your car going again.

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. Cylinder #4 misfire, PO304

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 use the flash-to-pass feature in a 2012 Ford Explorer?

The flash-to-pass feature flashes your high beams headlights briefly. To use this feature, pull the Turn Signal lever towards you slightly, and quickly release. Tip This feature can be used even when the headlights are not on.

Q: My turn signals don't work, can a local auto zone fix it?

The customer service professionals employed at most big chain auto parts retailers are not mechanics, but sale associates. Some locations will install wiper blades and replace batteries within reason, but these individuals are not necessarily trained in the repair of...

Q: Car struggles to go up hills and only goes 40-60 mph depending how steep the hill is. What's wrong with my car?

Hi there: Anytime a check engine light is illuminated it's because a sensor has detected a mechanical or electrical fault that impacts the vehicle's performance. If the mechanic you go to hasn't completed a check engine light inspection; which means...

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...
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...
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.