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2.3L ('02-'11) PO300 code diagnosis


DaveH

Active Member
Law Enforcement
Joined
Jan 21, 2023
Messages
150
Reaction score
84
Points
28
Location
sherwood Oregon
Vehicle Year
2005
Make / Model
Ranger XL
Engine Type
2.3 (4 Cylinder)
Engine Size
2.3
Transmission
Automatic
2.5 engine block 2.3 head with OEM ECU for the 2.3. I built this engine about 3 months ago and have about 3K on it. When first built it ran with multiple misfire codes and replaced plugs, wires and OEM coil. It cleared the code problem for about 2500 miles. The PO300 code is back this morning. There is no noticeable change in engine and runs smooth. So after a few pages of reading I am thinking, 1 fuel injector problem 2 Catalytic converter 3 O2 sensors, vacuum leak? Ideas on diagnosing this misfire issue before I throw more parts at it??
 


franklin2

Well-Known Member
Joined
Dec 24, 2019
Messages
3,586
Reaction score
1,844
Points
113
Location
Virginia
Vehicle Year
1984
Make / Model
Bronco II
Transmission
Manual
Check the pieces you replaced to repair it the last time. The parts you buy now are terrible as far as quality. I would ohm out the sparkplug wires you installed while wiggling them around. Don't get too rough with them, they seem to break too easily inside. If you have the old coil you could try putting it back in place.
 

DaveH

Active Member
Law Enforcement
Joined
Jan 21, 2023
Messages
150
Reaction score
84
Points
28
Location
sherwood Oregon
Vehicle Year
2005
Make / Model
Ranger XL
Engine Type
2.3 (4 Cylinder)
Engine Size
2.3
Transmission
Automatic
2.5 engine block 2.3 head with OEM ECU for the 2.3. I built this engine about 3 months ago and have about 3K on it. When first built it ran with multiple misfire codes and replaced plugs, wires and OEM coil. It cleared the code problem for about 2500 miles. The PO300 code is back this morning. There is no noticeable change in engine and runs smooth. So after a few pages of reading I am thinking, 1 fuel injector problem 2 Catalytic converter 3 O2 sensors, vacuum leak? Ideas on diagnosing this misfire issue before I throw more parts at it??
I pulled all plugs , looked perfect. Checked fuel pressure, 65 psi. Held fine after shut down. Did see the coil screws were not tight. Cleared the code and runs smooth as before. Will run to see if the code pops again.
 

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