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Dreaded P0301 code


bradne

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Sierra Vista, Arizona
Vehicle Year
2002
Make / Model
Ford
Transmission
Automatic
I recently came into possession a 2002 Ranger with a 3.0 V6 with 136xxx miles on the odometer. When I got it, it had a rough idle and the Check Engine Light was on. My OBD showed it as a P0301 code. I put in new plugs and wires (I am pretty sure they were original) and the engine now runs very smooth. I have never owned a Ranger before but it seems to run fairly strong. The problem is that the P0301 code keeps coming back. I can clear it, but it will come back after a day or so. I did a compression test and all the cylinders were between 125 to 150. #1 specifically had 150 on the compression test.

With that compression numbers should I even bother with a leakdown test? Where do I go from here to figure out this gremlin?
 


Bgunner

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Western Mass.
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Ford/Ranger XLT
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3.0 V6
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Manual
2WD / 4WD
2WD
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225/70/R15
My credo
If it's not broken Don't Fix It!
My understanding of the P0301 code is a misfire on a cylinder. Being an 2002 you should have DIS (Distributorless Ignition System) meaning coil packs to fire the spark. Try these suggestions to narrow it down:

1. At night, or dark garage, look to see if there is any spark running down the coil packs, down the out side of a plug or jumping from the wire to a ground. A very light mist of water from a spray bottle will sometimes help show the spark. Don't use to much as this can make the spark jump to the nearest ground when under normal conditions this wont happen.

2. Swap the plug wires on the coil pack that is giving you the code. The DIS uses waste spark and fire 2 plugs at the same time. If the code changes saying a different cylinder is misfiring then either the wire is bad or the Coil pack is bad.

While there are other reasons for misfires these are the most common.
 

bradne

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Thank You, swapping wires was actually my next thought since I read that the coil pack fires two cylinders at a time. I believe I should be able to swap the #1 wire with the #5 wire, is that correct?

I never thought about looking at the coil in the dark. I will try that too.
 

Bgunner

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113
Location
Western Mass.
Vehicle Year
1994
Make / Model
Ford/Ranger XLT
Engine Type
3.0 V6
Transmission
Manual
2WD / 4WD
2WD
Tire Size
225/70/R15
My credo
If it's not broken Don't Fix It!
Thank You, swapping wires was actually my next thought since I read that the coil pack fires two cylinders at a time. I believe I should be able to swap the #1 wire with the #5 wire, is that correct?
I believe it is #1 and #4, but I could be mistaken, that fire at the same time but here is the easy way to do it: if the computer is saying #1 misfire then trace #1 wire to the coil pack. Because it is a 6 cylinder there are 3 coil packs, once traced just swap the 2 on just that one coil pack. IF you want to know for sure that it is 1 and 4 firing trace the other wire to the cylinder. #1 is the right bank front and #4 is the left bank middle.
 

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