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Clayso, Master Automobile Technician
Category: Chevy
Satisfied Customers: 880
Experience:  ASE Master Certified Automobile Technician. 30 Years Experience.
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Just replaced plugs and wires. Running worse, Why, 2005

Customer Question

Just replaced plugs and wires. Running worse
JA: Have you checked all the fuses? Do you have a wiring diagram?
Customer: Why
JA: What is the model/year of your Chevy?
Customer: 2005 equinox 3.4
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes
JA: Anything else you think the mechanic should know?
Customer: Flashing po300
Submitted: 10 months ago.
Category: Chevy
Expert:  Clayso replied 10 months ago.

This is Clay, I'm a certified master automobile technician with 30 years of automotive repair and diagnostic experience.

From your description sounds like you have a defective plug wire(s) or a cracked spark plug(s). P0300 is a random cylinder misfire. See if the misfire can be duplicated by spraying down the wire and plug with a light mist of salty water. If need be have someone hold the brake with the vehicle in gear. Again wet down the plug wires one at a time with salty water and see if the misfire can be duplicated or changed in any way to isolate the problem cylinder(s).

You can check the ignition coils by disconnecting the plug wires. 6&3, 5&2, 4&1. The wires that are beside one another and with the engine running spark should jump from one tower to the other. This can be done with the 2 wires from one coil at a time. Kind of a back yard trick, but the spark should jump from one tower to the other clean and crisp.

Let me know if any of the old plugs removed looked really clean, this could be an indication of a cylinder head gasket leak.

I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.
Let me know

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