Intermittent misfire and lack of power

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Fyrboy55

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Joined
Jun 3, 2020
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15
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Middle TN
Ok all I have a 2005 Wrangler 4.0 RHD (if it matters) and it has an intermittent miss on multiple cylinders. I have checked / replaced the coil rail, New spark plugs (Autolite DBL platinums), looked under the cap of the oil pump drive assm, Did a compression check cold/hot Cold 160-180 / Hot 150-180, Checked fuel pressure 60 psi and still have the issue. It stutters upon takeoff like its only hitting on 3-4 cylinders and will eventually pick up and go. At highway speeds it acts kinda like the GM active fuel management and drops a few cylinders and eventually picks them back up. This is all random like I have a gremlin under the hood flipping a switch on / off as he pleases. I am now bald from pulling my hair out so any help would be great!

Also have checked for vacuum leaks and have fixed any I have found.

Thanks in Advance!
Jeremy
 
if youve done your coil pack, plugs. i'm at a loss. what supplies power to the rail? maybe try tinkering with that.

someone with more knowledge will chime in i'm sure.
 
Check and clean the throttle body including the iac. The problem could be the computer is getting bad info for the fuel side. Throttle position or mass air flow sensor.
But first (this is always first) check and clean all ground cables and battery cables. Confirm you have good voltage at the alternator and battery.
 
Goatman said:
Check and clean the throttle body including the iac. The problem could be the computer is getting bad info for the fuel side. Throttle position or mass air flow sensor.
But first (this is always first) check and clean all ground cables and battery cables. Confirm you have good voltage at the alternator and battery.
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Did a throttle body service with a full tune up and voltage looks good. Grounds checked and appeared clean I brushed them anyway with no change.
 
What code/codes are being set? Why did you replace the coil rail? What brand was the coil rail that you purchased? What is the Autolite part number of the plugs you installed?
 
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Daryl said:
What code/codes are being set? Why did you replace the coil rail? What brand was the coil rail that you purchased? What is the Autolite part number of the plugs you installed?
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P0300 is what shows and as far as I know the coil rail is original with cracked boots so I figured that was it. It was a BWD coil and the plugs are APP985.
 
Fyrboy55 said:
Will do. What’s the difference other than they are iridium. I went with the dbl plats cause that’s what I was reading everywhere. Just curious. Thanks
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The coil rail TJ’s are very temperamental with spark plugs and misfires. Just trying to rule out the simple things first. Please post back with your results. Also, save the old plugs and keep track of what cylinder they come out of in case we need to “read” the condition of them.
 
Daryl said:
The coil rail TJ’s are very temperamental with spark plugs and misfires. Just trying to rule out the simple things first. Please post back with your results. Also, save the old plugs and keep track of what cylinder they come out of in case we need to “read” the condition of them.
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I just had the app plugs out and they all look great but keep in mind they have around 100 miles on them now the original plugs were trashed. I could understand a misfire with the original plugs lol
 
Fyrboy55 said:
I just had the app plugs out and they all look great but keep in mind they have around 100 miles on them now the original plugs were trashed. I could understand a misfire with the original plugs lol
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The P0300 multiple cylinder misfires is a difficult one to diagnose as so many things can cause that. Always start with the plugs. Do you have the original coil rail?
 
Update: I had the battery unhooked overnight while I was working on other things and the next day it ran perfect and still is. Guessing it was something to do with the pcm?
 
Fyrboy55 said:
Update: I had the battery unhooked overnight while I was working on other things and the next day it ran perfect and still is. Guessing it was something to do with the pcm?
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Maybe the action of removing & reinstalling the battery cables improved the connections at the battery. Maybe the PCM just needed a reboot. Thanks for coming back and posting the solution.
 
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