So my 06 started throwing the dreaded P0303 code last year and after throwing some money and a lot of time at it I think its resolved.
History: After buying my TJ in early 21 with 112k I decided to do some preventive maintenance which included a set of Autolite APP985s. Everything was good for a year or so and then the dreaded P0303 code appeared. As you all know, that there can be a myriad of reasons for this code. It would only throw the code after the engine heated up. After much research on this forum I figured that since the plugs were relatively new and the correct type it must be caused by heat sinking or failure of the injectors. So I bought new 4 hole injectors and a heat shield kit from K Suspensions. The kit included manifold, fuel rail and injector shielding. The code still persisted. Thinking now that it was the coil pack I tested it to see if there was spark on all the plugs (per Youtube) and checked to make sure the contacts were correctly aligned. All checked OK. Next I did a compression check. Again all within spec. When I pulled the plugs #3 was discolored (see pic below). I turned the engine over and found that fuel was entering the #3 cylinder and again compression was within specs. I painstakingly inspected all the wiring for breaks or chaffing. Again no issues found. I decided to swap the #3 and #4 plugs. I ran it and after the engine warmed up it threw the P0304 code this time. This was my aha moment. I bought a new plug and installed it. Very long story short that $7 purchase seems to have fixed the issue. The plug that failed only had around 100 miles on it.
On the bright side I’ve become adept at pulling the coil pack and have become intimate with the engine.
History: After buying my TJ in early 21 with 112k I decided to do some preventive maintenance which included a set of Autolite APP985s. Everything was good for a year or so and then the dreaded P0303 code appeared. As you all know, that there can be a myriad of reasons for this code. It would only throw the code after the engine heated up. After much research on this forum I figured that since the plugs were relatively new and the correct type it must be caused by heat sinking or failure of the injectors. So I bought new 4 hole injectors and a heat shield kit from K Suspensions. The kit included manifold, fuel rail and injector shielding. The code still persisted. Thinking now that it was the coil pack I tested it to see if there was spark on all the plugs (per Youtube) and checked to make sure the contacts were correctly aligned. All checked OK. Next I did a compression check. Again all within spec. When I pulled the plugs #3 was discolored (see pic below). I turned the engine over and found that fuel was entering the #3 cylinder and again compression was within specs. I painstakingly inspected all the wiring for breaks or chaffing. Again no issues found. I decided to swap the #3 and #4 plugs. I ran it and after the engine warmed up it threw the P0304 code this time. This was my aha moment. I bought a new plug and installed it. Very long story short that $7 purchase seems to have fixed the issue. The plug that failed only had around 100 miles on it.
On the bright side I’ve become adept at pulling the coil pack and have become intimate with the engine.
