Code PO300, misfire, check engine light flashing and no power

IDACW

MEMBER
1998 PONTIAC SUNFIRE
2.4L
4 CYL
TURBO
2WD
AUTOMATIC
169,000 MILES

Okay, I have replaced the ignition manifold I have replaced the coil for spark plugs 1 and 4. I have put all new spark plugs and boots on car also have replaced the pulley tensioner. I have cleaned out the EGR valve and gasket I have got a brand new air filter in the car. Now the check engine light is on and flashing the whole time and the repair manual tells me if my check engine light is on and flashing giving me a p0300 code when hooked up to the obd II meaning I have a misfire somewhere that's why I replaced the coil, boots, and spark plugs. I can drive the car but just for me to go over the overpass a very slight incline the car will maybe only go 10 miles per hour and that's with the gas pedal floored all the way to the floor it also hesitates when it is shifting from one gear to the next. So it's taking about a minute and a half or more to switch gears to basically engage at all. I need to know the exact cause of problem to be able to fix it. I don't have the funds to replace things that will nor fix the problem as i'm not made of money. I need my car to run properly as i'm disabled and this is my only form of transportation for myself. Please help me someone give me a real diagnose of the cars issue at hand. Thanks Ida Walster of Lakewood, WA.

Friday, September 17th, 2021 AT 8:36 AM

1 Reply

AL514

MECHANIC
5,043 POSTS

Hello, is this car the GT or SE model? I'm assuming GT because it has a turbo?
Does the car smoke at all?
I will try to help you check some things without having to spend money and hopefully we can resolve this issue for you.
My first thought, because you have replaced pretty much all the ignition system parts. This car having a coil pack with 2 coils, 1 coil per 2 cylinders. p0300 is a random misfire code. So the reason you cant go over 10mph is either the vehicle is in "Limp Mode", this is a mode the ECM goes into to protect the vehicle from further damage by limiting the speed you can go. Or and I think this is your issue, the Catalytic Converter is melted down and clogged up the exhaust. This will cause the engine to not be able to take in any air because it cant let any exhaust out.
If you are able, you can do a couple things to check this.
First you can take out the Oxygen Sensor that is in front of the Converter
Or you can take the exhaust apart at the opening of the converter and see if you can restore power.
Note, these are only tests, the car will be very loud with the Converter unbolted, but if it restores power then you have found the problem,
Same with removing the front Oxygen Sensor. All you are doing is allowing the exhaust a place to escape.
You can try either of these things, they wont cost you anything. If it does not resolve the issue, then you will need to do further diagnostics. Random misfires can be caused by bad injectors, compression issues, etc.
Another test you can do that wont cost anything, take out the Fuel Pump relay and crank the car over. You have to listen very carefully to the sound of the car cranking over. It should be a very smooth consistent sound. You're taking out the Fuel Pump Relay so the car does not start.
If there's any variation in the way its cranking over, there is probably a compression issue. This is called "Cranking Cadence". You can Google/YouTube this to get a better understanding of what it should sound like.
Replacing the fuel filter is cheap as well, it should be done every 15,000-30,000 miles. My guess is that it has probable never been done.
I'm adding some guides to help as well as the Diagnostic Procedure. But I would check the Converter first.

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/engine-hesitates

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/engine-has-low-power-output

https://www.2carpros.com/articles/how-turbo-chargers-work

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