Please Help - CEL Trouble Code P0304 on 1996 Avalon

Hi all I am new to the YodaNation and have and issue leaving me



My wife has 1996 Avalon that recently had a flex pipe replaced, which I assume the misfiring engine caused the weak flex pipe to go pop. At the time I figured the CEL was on due to O2 sensors not getting the proper readings due to the lack of exhaust. Also figured that the major exhaust leak tha was directly under the engine made it seem like it was idling & driving rough. I learned that after the flex pipe was replaced by the exhaust shop that I was wrong. It was still running rough & the check engine light was still on, but hey at least it is quiet about it now .



The OBD II scanner is only pulling one code: P0304 aka Cylinder #4 Misfire. Even though the spark plugs were changed 10K miles ago. I swapped #4's SP with a new one, but without any improvement. So, I tested the resistance of cylinder #4 ignition coil. All was within spec with the primary coil testing at 0.8 ohms; secondary coil testing at 13K ohms. I decided to swap the coil from cylinder #6, JIC. At first it was running smoothly until 3 minutes into the test drive then back to it went. Clear the code, I was hoping for a cylinder 6 code that way I could blame the coil & be done with it. Instead it was still P0304.



Any ideas or suggestions are greatly appreciated. Thanks in advance.

Reply 1 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

What did the removed plug look like? Check the spark plug wire or maybe a fouled fuel injector. Try some Techron in the fuel and see if it improves.

Reply 2 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Possible bad injector

Reply 3 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

pardon me for being ignorant (my last car had a distributor), but what causes the coil to fire? just guessing, a 12V signal? maybe the 12V wire is bad.

Reply 4 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Here is a the best pic I could get of the spark plug.

Reply 5 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Also, as far as Techron is concerned is there a major difference between that & SeaFoam. The reason I ask is before I changed the replaced the valve cover gasket, spark plug seals, spark plugs, cleaned the throttle body, & changed the oil this last spring. I seafoamed everything... added to crank case, added to fuel tank, & drove around for about a week (60 -80 miles). Then, slowly poured into the vacuum line, turned over, let sit, & finally sat back & watched smoke show. Everything has been smooth operating since then. Also, is there a method to test the injector if so what's the process?

Reply 6 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Thanks to everyone for the suggestions so far. Sorry haven't had a chance to trouble shoot more since I was doing the wheel & spindle bearings on my truck last night. Once I get some time I will check the 12v signal at the coil. If that's good I will pull the #4 & #6 fuel injectors, clean them, and swap them. If that doesn't fix it or last move the misfiring cylinder to #6 so I can at least blame the injector. I don't know where else to look, but I will keep everyone posted on what I find.

Reply 7 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

The plug doesn't look bad. I prefer pure Techron for cleaning the injectors on the car. The Toyota product is repackaged Techron.

Reply 8 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Thanks again to everyone for their input. I found out the problem back in December, but I fell into my own pet peve of not posting the final resolution & closing up the post. The injector was in fact bad, I tested it's resistance & discovered it didn't have any.

Reply 9 : Please Help - CEL Trouble Code P0304 on 1996 Avalon

Great! Thanks for the feedback.