P0303 Back

[blacknsilver05]

So i had this problem probably about 6 months ago and I never figured out what it was, but it went away on its on eventually. I though it was gone for good until today. when 303 popped up again. It occurs while cruising at 2500 to 3000+ rpm. Its been in both fourth and fifth gear. I haven't tried to make it happen in 1st, 2nd or Third considering I don't really cruise in those gears. I have had the misfire code for 1, 3, 4, 5 but 3 has been very consistent. 1, 4, 5 happened maybe once or twice through the months that this was occurring. My sparks are not old, all coils work, injectors are clean and ive got a new battery. What else could it be that i'm missing? Thank you for your help.

 

[BruceH]

What kind of spark plugs and coils do you have?

 

[blacknsilver05]

I used champion 1 piece when i replaced the plugs, and my coils are all pretty much stock except for two that are oem replacements.

 

[BruceH]

I used champion 1 piece when i replaced the plugs, and my coils are all pretty much stock except for two that are oem replacements.

The only HT plugs that are known to be reliable are Autolite. I'd start with a new set of plugs. Either Autolite or Motorcraft.

That's why I asked. Almost always this problem is due to not using stock plugs. Brisk and to a lesser degree Champion are usually involved with spark issues. Aftermarket coils are to but since you have oem it probably isn't the case. You could swap coils and see if the problem swaps cylinders too.

 

[blacknsilver05]

Ok but if the problem is the plugs, why would the misfire only occur at a certain rpm range? If the plugs were bad wouldnt this happen randomly throughout the range?

 

[blacknsilver05]

And this problem did start before i changed the plugs. My original ones were bad so i thought they were the problem.

 

[BruceH]

Ok but if the problem is the plugs, why would the misfire only occur at a certain rpm range? If the plugs were bad wouldnt this happen randomly throughout the range?

I don't know. Vibrations? There is no guarantee it's the plugs, it's nothing more than an internet best guess based on others experiences.

What do we have to choose from? Plug, coil, wiring. You could still swap coils.

 

[BruceH]

And this problem did start before i changed the plugs. My original ones were bad so i thought they were the problem.

Started then went away when you changed plugs, correct? Then it came back. Sure does sound like bad plugs to me. Maybe one just loosened up? Have you checked connections and the plug itself?

 

[blacknsilver05]

Ive swapped coils around to see if it follows but that was a while ago. I was going to attempt that tomorrow again. What wiring?

 

[blacknsilver05]

Maybe one did loosen up I could check that also. I have not check connections or the plugs since changing them. I was just assuming they werent the problem since they were changed. Maybe ive been overlooking the problem though.

 

[BruceH]

Ive swapped coils around to see if it follows but that was a while ago. I was going to attempt that tomorrow again. What wiring?

Wiring to the coil and the connector itself which is doubtful. The boots have a spring in them that transmits the spark from the coil to the plug. Once again doubtful.

You have to start somewhere.

 

[blacknsilver05]

Ok ill report back tomorrow after I check the sparks. Thank you for the info for now.