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: Car intermittently won't start

Hi there. An intermittent no start condition, can be difficult to diagnose. Replacing the fuel filter would not hurt anything, especially if it hasn't been replaced in the last 30,000 miles. Diagnostic procedures should be performed, at the time of...

Q: Check engine light comes on and engine stalls but starts right back up. Upon restart the check engine light is off with no problems.

Hi there. It seems that there could be a loose wire or loose ground to the transmission sensors. First you will need to get a scanner and scan for any codes that are pending or stored in the ECM (computer)....

Q: Black smoke on my bumper from exhaust 03 cavalier?

Black smoke coming from the exhaust is usually an indication of a rich fuel condition. When this happens, this can be the result of many things such as faulty fuel injectors, a failing mass air flow sensor or a faulty...

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...
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...