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Check Engine light - P0301 code

655 Views 13 Replies 6 Participants Last post by  RT27
I was on the interstate today and my check engine light came on. I was driving about 70mph/3000rpm and my speed started dropping steadily. The rpm stayed the same. I pulled off the interstate to a complete stop. It was idling very rough when I stopped. I was able to accelerate for a bit back on the interstate then the problem repeated. Luckily I didn't have far to go. I found several possible causes for this like bad spark plug, bad plug wire, bad coil pack, and bad/dirty fuel injector. Can anyone help me more specifically target the problem based on the problems I'm experiencing?
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· Administrator
マズダスピード3
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Double check the gap on the electrode armature to make sure it’s in spec.

A test you can perform is to pull the plug and attach it to the coil pack and lay it on the valve cover. Crank the engine over to see what color the spark is.

There’s a spring in the coil pack that stretches over time. Try swapping coil pack and plug to verify its moving to another cylinder.
 

· just a nobody
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Swapping the parts around is mainly to determine what may be causing the code!
If the code went with the part to the cylinder where it went to, then your issue is with the part and not the cylinder itself.
In your case, it looks like it is the cylinder since you are getting the same code! Would start with a compression test!
What is the mileage of the vehicle and condition?
 

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Discussion Starter · #9 ·
Update: after watching a few other videos, I went back and unhooked the coils while the engine was running. The 1st coil was bad and didn't make an obvious difference in the engine idle while the other 3 did. I replaced the coil and it's back to normal. Thanks everyone for the help! This was a big learning experience.
 

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This issue has happened to me before. The time it happened, I got a P0304, but swapped with cylinder 1. Cleared the code and got both P0301 and 304.

At first when I removed the plug from cylinder 4, I hadn’t noticed that the electrode left the chat. Tried swapping the coil packs too and got same results. Found oil buildup in the spark plug tube seals. Replaced the seals and valve cover gasket, along with new set of plugs and coils.
 

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Double check the gap on the electrode armature to make sure it’s in spec.

A test you can perform is to pull the plug and attach it to the coil pack and lay it on the valve cover. Crank the engine over to see what color the spark is.

There’s a spring in the coil pack that stretches over time. Try swapping coil pack and plug to verify its moving to another cylinder.
Check engine codes first, use it to track issue mine did similar with knock sensor gone bad
 
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