Q: Have a 2004 Trailblazer with the 4.2L. Idles rough and throws a "P0300" "Engine Misfire" DTC... Suggestions?

asked by on

Car died on the wife a couple days ago, lost power, dash light came on to "stop engine" as well as "low oil pressure". Suggestion was that the fuel pump or filter were bad because of the power loss. Changed the filter, car started eventually and runs now. It's throwing a P0300 engine code and running rough. Trying to figure out where to look. I have had to replace a coil once, the code it threw then was cylinder specific.. Now it seems more generic...

My car has 149000 miles.
My car has an automatic transmission.

It sounds like you could be having an issue with your fuel system. It is possible that the replacement of the fuel filter helped the issue but did not resolve it completely. I would recommend having your fuel pressure tested by a qualified professional and have it compared to the manufacturer’s specification. If the fuel pressure is low, it is possible that the fuel pump or fuel pressure regulator could be causing this issue. If these parts turn out to be working properly, I would then check the injectors for proper function.

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. Have a 2004 Trailblazer with the 4.2L. Idles rough and throws a "P0300" "Engine Misfire" DTC... Suggestions?

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: Truck won't shift out of first gear - 1979 Chevrolet C10

Hello. There are several possibilities here: the vacuum modulator valve, the governor in the transmission, or possibly incorrect fluid level in the transmission. If you would like to have this checked, a qualified professional from YourMechanic can come to your...

Q: I cleaned the ECM/PCM and now my car won't stay on

Whenever the ECM is disconnected the idle control settings the ECM has stored in memory will be cleared. The ECM will revert to the factory-new settings and since the engine now has high mileage and the need for adjustments to...

Q: My car alarm keeps randomly going off at night or during a storm. I know one of my door sensors is messed up and it thinks it's op

The alarm system cannot be bypassed to disable the alarm. you will need to locate and repair the defective door latch in order to fix the issue. I know this is not what you wanted to hear but the manufacturer...

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...
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...