New from North Dakota: P0303 code and cylinder 3 misfire

Ian

Ian

Member
Joined
Apr 13, 2017
Messages
49
Location
North Dakota, United States
I have a 2005 TJ 4.0 and I joined for some help. I have a P0303 code which is cylinder 3 misfire. Things I have done so far include all new spark plugs, new coil rail, new o2 sensors, swapped the first fuel injector with the third fuel injector, and a new crank position sensor. Only thing I can think of left before I take the head off is a cam position sensor. It's not making ticking noises like a lifter tick would. It's doggy and that's about all. Any help is greatly appreciated. Thanks in advance.
 
  • Like
Reactions: 94c2500
Welcome to the forum! What brand of O2 sensors and crankshaft position sensor did you use as replacements?
 
I'd replace the CPS with a Mopar OE sensor. Our Jeeps are well known not to like aftermarket sensors.

Which plugs did you use? I know these things are also very sensitive to the type of plug used.
 
Use this method to test your coil packs as well:


That will tell you for sure if they are all actually firing.
 
  • Like
Reactions: Ian
Ian said:
Champion plugs. Had autolights before that.
Click to expand...
Exactly which Champion plugs? Hopefully not the 3034 which will cause problems.

But your #3 misfire is more than likely caused by the issue mentioned by TJDave above. The #3 fuel injector can vaporize its fuel inside from engine heat and cause a misfire. The TSB he provided information on is basically wrapping that insulator sleeve around the #3 fuel injector to prevent that from happening. I also had a #3 misfire that was cured by that insulator.
 
  • Like
Reactions: Ian
For those who like pictures... ;)
IMG_00035B15D.jpg
 
  • Like
Reactions: Infernicus, Ian, Chris and 1 other person
Ian said:
What spark plugs do you suggest?
Click to expand...

What are the best spark plugs for my Jeep Wrangler TJ 4.0?

@Jerry Bransford wrote that thread, it's very informative. It's honestly worth a read.

However, here's the except from it that tells you what plugs you want:

I always recommend dual-tipped Platinum or Iridium spark plugs which will perform well for at least 100K miles. Iridium tipped plugs will last significantly longer than even the 100K miles dual-tipped platinum plugs will.

Good dual-tipped platinum plugs include the Autolite APP985 and Champion 7034. The NGK 7866 laser iridium spark plug is also a good choice as well.

A good iridium tipped plug for the 4.0 engine would be the Autolite XP985. A technical trainer at I know at Autolite checked his iridium plugs at 165K miles and they showed no visible wear.

Such plugs last so long that it's a good idea to smear a dab of copper-based antiseize onto their threads before screwing them into the head. Make sure no antiseize gets onto the electrodes (tip).

So while conventional plugs are what the factory installs and they are the cheapest, that doesn't mean they are the best choice for replacement spark plugs.​
 
  • Like
Reactions: Ian
Ian said:
I have a 2005 TJ 4.0 and I joined for some help. I have a P0303 code which is cylinder 3 misfire. Things I have done so far include all new spark plugs, new coil rail, new o2 sensors, swapped the first fuel injector with the third fuel injector, and a new crank position sensor. Only thing I can think of left before I take the head off is a cam position sensor. It's not making ticking noises like a lifter tick would. It's doggy and that's about all. Any help is greatly appreciated. Thanks in advance.
Click to expand...


In addition to the injector wrap that was mentioned, I'd be sure to check the foil insulation blanket that sits on top of the Intake manifold. It may look ok, but deteriorate and lose effectiveness. Mine looked outwardly just fine, but when I moved it around, it just came apart in pieces. I actually stacked two new blankets together.
IMG_20170331_150314.jpg


71skIXlfqYL._SL1500_.jpg
71skIXlfqYL._SL1500_.jpg
IMG_20170331_150314.jpg
 
  • Like
Reactions: Chris and Ian
Chris said:
@Jerry Bransford knows for sure, but I believe it goes around the injector:

Here's Jerry's thread on it:
TSB: 18-031-03 (4.0L Rough Engine Idle After Restart Following A Hot Soak)
Click to expand...

Just realized this article is for 2000-2004 and I have a 2005. And I have reset the code and started my jeep cold and the code popped back up in less than 30 seconds. This makes me think it has nothing to do with heat but I am still going to put the heat shields on it because it won't hurt. Also didn't get a chance to test my coil pack and I won't be home until tuesday.
 
Last edited:
  • Like
Reactions: Chris and 94c2500
Top Bottom
Back