Running Rough with P0304 Code SOLVED, New Member

This site and those like it have me helped me alot over the years. Time for me to join and contribute.
On my way to the dump over the weekend my 2000 Tundra w 4.7L suddenly started running rough, idling rough and had a flashing check engine light (CEL).
Stopped at Autozone to have them read codes, found a P0304 for Misfire on Cylinder Number 4. I figured it had to be either a spark plug, coil pack or injector. Purchased a set of plugs, coil pack and a scan tool.
For diagnosis, I figured it was easiest to shut to truck off, clear codes and then swap coil pack on cylinder #4 with another cylinder and then test drive to see if code followed coil pack or stayed with cylinder #4. I didn't open the new coil pack so that I could return it if it wasn't the problem. I swapped coil packs with cylinder #6 and test drove. Truck was still running rough but took a few miles for the CEL to start flashing again. I shut down and immediately read the code and was now getting a P0306, meaning the problem had followed the coil pack.
I replaced the coil pack and no more rough running or CEL. While I was in there I did pull a plug and found the gap to be over .040". Spec is .031"-.035" so a put a set of NGK platinums in it based on recommendations from this forum.
Thanks for all the help and I hope this will help someone else.

 

Good job. I would have used the same diagnostic process working on a customer’s car.

 

Hiya and welcome from SoCalif!!!

 

Welcome from East Tennessee.Great job on how you diagnosed the problem. Sometimes you have to just stand back and think the problem and solution through!

 

Good job in the diagnosis and write up. Had the same situation last year happen and replaced just coil pack #3.

Since then, I replaced all coil packs with new OEM Densos along with OEM Denso Plugs per manual.


I am selling some of those used OEM coils with 158k miles for a fair price to be used as back ups to keep on your truck for emergencies, as a swap confirmation, and replacement for ?miles?. While being a used product, they may last a lot longer than the cheap China made coils online from the reviews read. If you can do it I highly recommend spending the extra on OEM new Denso.

Selling (one) box of 2 and (one) box of 3. All in working order. Check out descriptions in for sale link below.

https://www.tundras.com/threads/first-gen-oem-denso-ignition-coils-used.35152/

 

WwlcWel from Texas

 

Welcome to the party!!

 

Welcome from Ohio!