Q: Still getting code P0300 after parts change

asked by on

I am getting error code P0300, Random Multiple Misfires. I have replaced various parts in the engine, including the ICM, three coils, six fuel injectors, and both the upper and lower O-rings. I also replaced the lower intake manifold gasket, the entire upper manifold, all six spark plugs and wires, and the fuel pressure regulator. I am still getting an error code P0300. I ran a fuel pressure test and the leak down shows pressure loss.

It sounds as though you have done an almost complete tune-up of the vehicle. However, there may be a few components left to check.

A clogged fuel filter can restrict fuel volume causing a lean condition, and set random multiple misfires as all cylinders are lean. I believe your year model does come with a serviceable fuel filter; your vehicle lies on the border of model change where serviceable fuel filters were replaced with a filter in the fuel pump assembly. Handling volatile liquids can be very dangerous, so I would suggest having a trained mechanic, like the ones at YourMechanic, assist with a fuel filter replacement.

Also, a certified mechanic will be able to verify fuel pressure loss or a low fuel pressure situation with a comprehensive engine misfire inspection, and lead your diagnosis from there.

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. Still getting code P0300 after parts change

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: My husbands gas guage has been messing up?

Hello, thank you for writing in. The fuel pump is part of a unit called the fuel module. The module also houses a float that raises and lowers with the level of the fuel. That movement is then translated into...

Q: I need to replace the harmonic balancer on my 94 buick. Is it ok to drive to go pick up the parts?

If the harmonic balancer is known to be defective, the only prudent course is to not operate the engine until the balancer is replaced. There are at least two risks: 1) the balancer could completely separate causing further damage; and...

Q: Service Engine Soon Light came on yesterday.

While the oxygen sensor may be the cause of the service engine soon light coming on, it's best to have a certified technician correctly diagnose why the service engine light is on. When the service engine soon - or check...

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...
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...
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...