Cylinder misfiring and ghost P0303 code

0121whit

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Tifton, Georgia
Cut quick to the point, I’ve got a misfire on cylinder 3. What I’ve done.
Checked for vacuum leaks: none
Heat shielded injectors: all of them
Checked compression: within spec on all 6
Checked fuel pressure :within spec
New fuel pump
O2 sensors: all 4 new
New plugs
New coil
New cam synchronizer and OPDA
New crank sensor
New thermostat and water pump
New fuel injector connectors
New maf sensor
New IAC valve
New throttle position sensor
New intake air temp sensor
New entire evap system
New vacuum lines
Checked all wires running behind valve cover for cuts and grounding problems



I’m at my wits end.
 
Cut quick to the point, I’ve got a misfire on cylinder 3. What I’ve done.
Checked for vacuum leaks: none
Heat shielded injectors: all of them
Checked compression: within spec on all 6
Checked fuel pressure :within spec
New fuel pump
O2 sensors: all 4 new
New plugs
New coil
New cam synchronizer and OPDA
New crank sensor
New thermostat and water pump
New fuel injector connectors
New maf sensor
New IAC valve
New throttle position sensor
New intake air temp sensor
New entire evap system
New vacuum lines
Checked all wires running behind valve cover for cuts and grounding problems



I’m at my wits end.

Or to start with, swap injector 3 with another to see if the misfire moves with it.

I actually have replaced them. I replaced them 2 days ago. I forgot to mention in post
 
I actually have replaced them. I replaced them 2 days ago. I forgot to mention in post

No codes other than cylinder 3 misfire? No other issues? With that being the case, and everything you've already done, I would start to wonder about the coil pack. I've never had to test one, so I'm not sure how to proceed. Maybe someone with more experience with that will chime in.
 
No codes other than cylinder 3 misfire? No other issues? With that being the case, and everything you've already done, I would start to wonder about the coil pack. I've never had to test one, so I'm not sure how to proceed. Maybe someone with more experience with that will chime in.

Checked it with a screwdriver and got the crap shocked out of me. It’s also a brand new one. I’m getting spark for sure. Even tried with an inline tester
 
Did the misfire exist prior to replacing all of the parts you replaced? In other words was it all replaced in an effort to fix the misfire?
 
Well it existed before hand but I replaced the plugs and coil and that solved it, then about a year later it started doing it again and I’ve just been throwing parts at it since because I cannot for the life of me figure it out.

I don't know when in this chain of events you tested things compared to when things were replaced, but just a reminder: Don't assume new parts = good parts. I made that mistake several times. If you haven't tested the coil or checked the plugs since you replaced them, I'd check again. I would assume there's a more scientific way to check the coil than with a screwdriver...something to ensure it has the proper spark, but I'm not positive what it is. I feel like it almost has to be related to a plug, coil, or injector since it's always cylinder 3, and nothing else is impacted.
 
A #3 misfire is common, my 04 developed it, but it is usually easily fixed. It's normally caused from heat from the exhaust header cooking/vaporizing the gasoline inside the #3 fuel injector. The factory released a TSB (technical service bulletin) to fix it which is nothing more than placing insulation around the #3 fuel injector which cured mine.

This is the exact p/n specified by Jeep to wrap around the injector, it's held in place by a small zip tie. The photo below is of mine after installing it 10-12 years ago with no more problems since.

https://www.amazon.com/gp/product/B007O3QHDK/?tag=wranglerorg-20

Yes I realize it says ignition shield but it's exactly what the factory TSB specified and it does a good job fixing the problem.

Fuel Injector Insulation .jpg
 
A #3 misfire is common, my 04 developed it, but it is usually easily fixed. It's normally caused from heat from the exhaust header cooking/vaporizing the gasoline inside the #3 fuel injector. The factory released a TSB (technical service bulletin) to fix it which is nothing more than placing insulation around the #3 fuel injector which cured mine.

This is the exact p/n specified by Jeep to wrap around the injector, it's held in place by a small zip tie. The photo below is of mine after installing it 10-12 years ago with no more problems since.

https://www.amazon.com/gp/product/B007O3QHDK/?tag=wranglerorg-20

Yes I realize it says ignition shield but it's exactly what the factory TSB specified and it does a good job fixing the problem.

View attachment 504736

I almost mentioned that earlier, but he listed in his first post that he had heat shielded all injectors. I just assumed this is what he meant.
 
I saw that but there's insulation and then there's insulation. I dunno what he used or how he did it. That's why I showed how the TSB for that problem is done.

I used the mopar recommended heat shielding. The ignition shields. Also I’ve replaced parts multiple times and checked everything and then double checked and made sure everything is working properly, and still to no avail
 
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I used the mopar recommended heat shielding. The ignition shields. Also I’ve replaced parts multiple times and checked everything and then double checked and made sure everything is working properly, and still to no avail
Good decisions there. Now that we're grasping at straws.... I read where you replaced your spark plugs, EXACTLY what model # and brand of spark plugs did you install? There is a type of spark plug called a single-tipped platinum where the platinum is only on one side of the gap. Like the Autolite AP-985 or Champion 3034, either of those can and do cause misfires in newer TJ 4.0 engines that have the waste-spark ignition design. Conventional copper-core spark plugs, double-tipped platinums like the Autolite APP-985 and Champion 7412, and iridium tipped plugs like the Autolite XP-985 work fine and won't cause misfires. And yes I know you're just having one cylinder misfiring but....
 
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Conventional copper-core spark plugs, double-tipped platinums like the Autolite APP-985 and Champion 7412, and iridium tipped plugs like the Autolite XP-985 work fine and won't cause misfires. And yes I know you're just having one cylinder misfiring but....

I definitely agree with this as well. I've seen a lot of misfires with new plugs fixed by putting in the "right" new plugs. The XP-985 is what I run and always recommend to others.
 
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Good decisions there. Now that we're grasping at straws.... I read where you replaced your spark plugs, EXACTLY what model # and brand of spark plugs did you install? There is a type of spark plug called a single-tipped platinum where the platinum is only on one side of the gap. Like the Autolite AP-985 or Champion 3034, either of those can and do cause misfires in newer TJ 4.0 engines that have the waste-spark ignition design. Conventional copper-core spark plugs, double-tipped platinums like the Autolite APP-985 and Champion 7412, and iridium tipped plugs like the Autolite XP-985 work fine and won't cause misfires. And yes I know you're just having one cylinder misfiring but....

I’m using champion 9034 plugs and also made sure they were gapped to spec before installation
 
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