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Looking for any help with the dreaded misfire issue

jimvski

New Member
Joined
Jun 22, 2021
Messages
18
Location
Philadelphia
Hello all,

We really need some help. My son has a 04 Rubi 4.0L 5-speed with about 142K on it. We've owned it since new. He suddenly started getting a misfire on cylinder 1. It initially threw the P0301 code. 95% of the time, it runs fine when it's cold, then starts to misfire when it's about half warmed up. Because it happens warmed up, I thought it was a bad sensor but so far no luck. Sometimes it's consistent, sometimes it's not. When I say not consistent, I mean sometimes it sounds like there's a couple misfires from different cylinders but no code to verify that. We've replaced almost every sensor with factory (or forum recommended) ones. We've tried 2 different brand plugs (also recommended here/APP985). Right now, it's a consistent miss on 1. I'm 99% sure it's cylinder 1 because we've pulled the fuel injector connector while it's missing and it made no change while pulling the others have caused a change in idle. Below is the list of what we've done. ANY ideas on where to go with this next? We did take it to a mechanic with no luck (what he did is listed below also). Thank anyone in advance for ANY suggestions. It's driving me nuts.

The ONE thing we've done that seems to give us a hint is that we pulled the coil rail, and grounded all the plugs directly to the battery and cranked the engine. The spark was yellow/weak and inconsistent. We've kept a battery charger hooked up to the battery to make sure it has plenty of power. We also tried jumping another battery to it.

1. Changed the 2 upstream O2 sensors
2. New Cam sensor
3. new crank sensor
4. tested injectors, #1 was reading low so it was replaced.
5. new coil rail
6. New MAP sensor
7. new coolant temp sensor
8. checked compression - was OK.
9. Ran a can of seafoam through
10. New plugs (2 different kinds, also tried adjusting the gap)
11. Getting full power (12+V) at the injector (checked #1)
12. looked for vacuum leaks and haven't found any
13. We recently had the valve cover off and the oil pan off - engine internals looked impeccable.

Mechanic:
1. Checked compression
2. scoped engine
3. checked fuel system
 
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jimvski

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Joined
Jun 22, 2021
Messages
18
Location
Philadelphia
Did you install store brand or Mopar sensors, coil rail, etc. ?
My son purchased them but I know he went with the info from this forum. I’m going to triple check with him again tomorrow but i know he said the o2s were ngk/ntk. Most of it was mail order but I know nothing came from places like autozone/pep boys, etc.
 

CodaMan

California Escapee
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Mar 9, 2017
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4,594
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Dover, Arkansas
Is the PCM pulsing the injector like it should be? A NOID will test that.

I also did a write-up on troubleshooting that problem.

 
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rasband

Balls Deep
Supporting Member
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Sep 11, 2018
Messages
7,291
Location
Highlands Ranch, CO
We really need some help. My son has a 04 Rubi 4.0L 5-speed with about 142K on it. We've owned it since new. He suddenly started getting a misfire on cylinder 1.
Just to check, was any service performed on the Jeep between the time it was running fine and when there was a misfire?

If not:

I'd check for a short to ground, it's fairly common at the back of the valve cover where the bolt sticks up into the loom against the fire wall. It is also somewhat likely between the bell housing and the fire wall pinch seam. If it's not that, I would start to think the PCM may be faulty, but Mark (@Wranglerfix) can confirm if these are issues he sees in the 04 year.
 
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Wranglerfix

TJ Enthusiast
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May 2, 2019
Messages
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Location
Hollywood, Fl
@jimvski The 0301 code lead back to:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

I can test your ecm on a simulator if you would like to send it in to me. I don’t charge anything to test them and 125 for repairsif necessary.
 
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jimvski

New Member
Joined
Jun 22, 2021
Messages
18
Location
Philadelphia
My son purchased them but I know he went with the info from this forum. I’m going to triple check with him again tomorrow but i know he said the o2s were ngk/ntk. Most of it was mail order but I know nothing came from places like autozone/pep boys, etc.
First of all - thank you everyone for the replies so far.

Here's what my son says he bought:

MAP Sensor - Mopar
Fuel Injector 1 - Mopar
Coolant Temperature Sensor - Mopar
Coil Pack - Mopar
Spark Plugs - Standard coppers / Autolite APP985
Crankshaft Position Sensor - Mopar
Camshaft Position Sensor - NGK OPDA -
Crown Automotive Ignition Capacitor -
Crown Automotive Upstream O2 Sensors - NTK

as far as service on the Jeep prior to the misfire - we're always tinkering on it but nothing was done immediately before. I've disconnected the battery overnight to make sure the ECM is completely reset so we'll see if that does anything. My thoughts are that it's something electrical so we'll take a look at the loom back near the firewall. I'll post any results.
 

Rob L.

TJ Enthusiast
Joined
May 7, 2021
Messages
155
Location
Tennessee
Try a leak down test.

I had a misfire on the same cylinder and it was a bad/leaking intake valve. Couldn't tell that from compression test in my case
 
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jimvski

New Member
Joined
Jun 22, 2021
Messages
18
Location
Philadelphia
First of all - thank you everyone for the replies so far.

Here's what my son says he bought:

MAP Sensor - Mopar
Fuel Injector 1 - Mopar
Coolant Temperature Sensor - Mopar
Coil Pack - Mopar
Spark Plugs - Standard coppers / Autolite APP985
Crankshaft Position Sensor - Mopar
Camshaft Position Sensor - NGK OPDA -
Crown Automotive Ignition Capacitor -
Crown Automotive Upstream O2 Sensors - NTK

as far as service on the Jeep prior to the misfire - we're always tinkering on it but nothing was done immediately before. I've disconnected the battery overnight to make sure the ECM is completely reset so we'll see if that does anything. My thoughts are that it's something electrical so we'll take a look at the loom back near the firewall. I'll post any results.
OK - interesting new twist. PCM reset didn't do anything. But while we were messing around we were unplugging injector1. When we unplugged it, nothing changed but when we'd plug it back in, the misfire would go away for 1 rotation. So, my thinking is there may be a clog restricting the flow to injector 1. My theory is when we unplug it, the pressure builds up, then when we plug it in, it injects the fuel and the cylinder fires. Crazy theory but all the logical conclusions have been tried. We're going to pull the fuel rail, thoroughly clean it and see what happens.
 
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Rob L.

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May 7, 2021
Messages
155
Location
Tennessee
OK - interesting new twist. PCM reset didn't do anything. But while we were messing around we were unplugging injector1. When we unplugged it, nothing changed but when we'd plug it back in, the misfire would go away for 1 rotation. So, my thinking is there may be a clog restricting the flow to injector 1. My theory is when we unplug it, the pressure builds up, then when we plug it in, it injects the fuel and the cylinder fires. Crazy theory but all the logical conclusions have been tried. We're going to pull the fuel rail, thoroughly clean it and see what happens.
I'd go ahead and swap that injector with another and see if it follows it since you're taking the rail off.
 
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jimvski

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Jun 22, 2021
Messages
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Location
Philadelphia
I'd go ahead and swap that injector with another and see if it follows it since you're taking the rail off.
Thanks. We tested that injector when this all started and the resistance was low so we replaced it. Probably should have cleaned the rail then!! We’ll clean it, swap them, and play around to see what happens.
 
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jimvski

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Jun 22, 2021
Messages
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Location
Philadelphia
@jimvski The 0301 code lead back to:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

I can test your ecm on a simulator if you would like to send it in to me. I don’t charge anything to test them and 125 for repairsif necessary.
@Wranglerfix - We have a Jamboree coming up in a few weeks and we're running out of ideas so I think we'd like to take you up on your offer to test it. How/where do I send it?
 
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Wranglerfix

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Hollywood, Fl
@Wranglerfix - We have a Jamboree coming up in a few weeks and we're running out of ideas so I think we'd like to take you up on your offer to test it. How/where do I send it?
Wranglerfix, LLC
2350 N University Drive
#849085
Pembroke Pines, Fl 33084

Please put all of your contact information inside as well as any codes or symptoms that you were having.

Thanks,

Mark
 

Thedogsbollocks

TJ Enthusiast
Joined
Jan 4, 2020
Messages
183
Location
Florida
So , I’ve had and posted about a similar issue and questioned if the fuel pump check valve issue caused this as a consequence.
In the end...by accident I found a tiny split in the hose from the valve cover to the air filter box. I replaced the hose and the issue with the #1 mis fire has gone. I’m amazed this was the cause but in my case it was. Just a thought.
Ps my issues was a ‘lumpy’ idle when at lights for example not exactly your issue but hey...worth a check
 
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jimvski

New Member
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Jun 22, 2021
Messages
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Location
Philadelphia
Wranglerfix, LLC
2350 N University Drive
#849085
Pembroke Pines, Fl 33084

Please put all of your contact information inside as well as any codes or symptoms that you were having.

Thanks,

Mark
Mark,

Thanks. What's your turnaround time? We're supposed to go on a Jamboree 7/8 and trying to decide whether to send it now or keep working on it and send it after if we can't get it figured out.
 
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jimvski

New Member
Joined
Jun 22, 2021
Messages
18
Location
Philadelphia
So , I’ve had and posted about a similar issue and questioned if the fuel pump check valve issue caused this as a consequence.
In the end...by accident I found a tiny split in the hose from the valve cover to the air filter box. I replaced the hose and the issue with the #1 mis fire has gone. I’m amazed this was the cause but in my case it was. Just a thought.
Ps my issues was a ‘lumpy’ idle when at lights for example not exactly your issue but hey...worth a check
Thanks for the info. we're working on it right now trying to find what ever might be the cause - we'll give that a look.
 
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jimvski

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Jun 22, 2021
Messages
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Location
Philadelphia
First of all - thanks to everyone who replied. We spent some good time on Sunday testing - fuel, electrical, etc. It looks like Rob might be the winner with the leak down test. I didn't have leak down tester so we put cylinder 1 at TDC, put in 60PSI of air and could actually feel the air coming out of the tailpipe so definitely seems to be an exhaust valve issue. Tried it with cylinder 5 just to compare and no air. We're pulling the head tonight to get a look inside. I'll post what we find. The mechanic and I both had good compression tests so I didn't think this was the issue but we'll see soon.
 
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rlinares40

Member
Joined
May 19, 2020
Messages
53
Location
Mckinney, Texas
I had been chasing down a P301 and a P300 for a while changed absolutely everything. All new mopar sensors, new cylinder head and the problem would persist. Finally did a leak down test and the shop noticed that I was losing about 20% in cylinder 1 from what they said. Finally decided to pull the engine and do a rebuild and this is what I found:
1.jpg


So although you're getting a P301 misfire it could be another cylinder because the above picture was my #2 piston.
 

Jeffseven777

Man Bear Pig
Supporting Member
Joined
May 25, 2021
Messages
614
Location
Ohio
ewww. i had 2 cracked pistons. in my 4 banger had to rebuild whole engine.

Well hopefully ur bad valvue is just burnt and nothing to crazy