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Repeated Misfire Codes


Obie

New Member
Joined
Feb 9, 2019
Messages
19
Location
North Alabama
Hello everyone, new here.
I'm currently trying out a 2001 TJ. It belongs to a coworker that is as OCD as i am about vehicles.
As i was begining to back out of his shop the engine light came on. He has owned since 2011 and said he'd never seen that light. (I believe him)
My code reader indicates a P0302 & P0305 (very popular I've learned) not sure why these 2?

*Worth noting: I stated the engine and noticed he was having trouble unlocking the rollup door I shut it off so not to fill the shop with exhaust. Within a few seconds the door started up so i restated the engine and that's when the light came on.
I cleared those 2 codes and they reappeared the next time I drove it.
So is the $$chase on or does the 2 and 5 have a common part fix?
 

KCsTJ

TJ student
Supporting Member
Joined
Jan 9, 2018
Messages
2,882
Location
Farmersville, TX, United States
The chase is on my friend.
Since the misfires are on two specific cylinders I would rule out something general like the crankshaft sensor for example, for now.
Lots of different things can cause a misfire which makes it tough to diagnose quickly.
Focus on cylinders 2 & 5 and look closely for anything obvious from the spark plug to the PCM.
Ideally a high end diagnostic machine is the best, quickest way but we jeep heads dont own these expensive things.
See if a hand held reader gives you more info.
 

Jerry Bransford

TJ Guru Moderator
Staff Member
Supporting Member
Joined
Nov 9, 2015
Messages
15,353
Location
Escondido California
The three coil rail coils are paired to two cylinders each.

1 and 6
5 and 2
3 and 4

As you can see, 2 & 5 are fired by the same coil on your coil rail. I'd reseat the connector to the coil rail and reseat the coil rail itself over the spark plugs. If that doesn't fix it I'd be highly suspicious of a bad coil rail.
 
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Obie

New Member
Joined
Feb 9, 2019
Messages
19
Location
North Alabama
The three coil rail coils are paired to two cylinders each.

1 and 6
5 and 2
3 and 4

As you can see, 2 & 5 are fired by the same coil on your coil rail. I'd reseat the connector to the coil rail and reseat the coil rail itself over the spark plugs. If that doesn't fix it I'd be highly suspicious of a bad coil rail.
Thanks, that's what i wanted to confirm. Wasn't absolutely sure the pairing if any. Most search results mention single codes so was hoping 2 at the same instance would lead me to a quicker resolve. Thanks again
 
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Obie

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Joined
Feb 9, 2019
Messages
19
Location
North Alabama
Did I see on this forum, over the weekend, when talking about the misfire codes that champion 7034 plugs were strongly recommended?
 
OP
YooperSkipper

YooperSkipper

Member
Joined
Jan 31, 2018
Messages
54
Location
Michigan, United States
Sorry about being so late in replying to everyone's comments/suggestions but I've been out of town and away from my TJ! Since my return, I've been driving it a little with the same results as before....after about 3-4 miles the CEL starts flashing for about 30 seconds and then stays lit with a miss in the engine as well. I turn off the engine, plug my OD reader, read the code(s)....301 mostly with occasional 302 & 300. I have just been erasing them and when I restart the engine it runs fine....sometimes all day....sometimes not! What baffles me is if something was seriously wrong it should be there all the time....right? Does it hurt to do what I'm doing by erasing the error codes?
 
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OP
YooperSkipper

YooperSkipper

Member
Joined
Jan 31, 2018
Messages
54
Location
Michigan, United States
The three coil rail coils are paired to two cylinders each.

1 and 6
5 and 2
3 and 4

As you can see, 2 & 5 are fired by the same coil on your coil rail. I'd reseat the connector to the coil rail and reseat the coil rail itself over the spark plugs. If that doesn't fix it I'd be highly suspicious of a bad coil rail.
I’m confused......I’ve been told repeatedly that the individual coils were paired on cylinders 1 & 2, 3 & 4, 5 & 6. Which is it?
 

Kawi413p

New Member
Joined
Jan 4, 2020
Messages
11
Location
California
Thanks....I’ll give this to the “mechanic” who told me my misfire codes on cylinders 1 & 2 definitely pointed to a bad coil on the rail that serves those cylinders! New to a wrangler but am learning fast! Thanks again!
Were you ever able to get the misfire solved? I’be been trying to track down mine for awhile now.
 

Jeepn_Texas

TJ Enthusiast
Joined
Jan 13, 2020
Messages
123
Location
Houston, TX
Hello everyone, new here.
I'm currently trying out a 2001 TJ. It belongs to a coworker that is as OCD as i am about vehicles.
As i was begining to back out of his shop the engine light came on. He has owned since 2011 and said he'd never seen that light. (I believe him)
My code reader indicates a P0302 & P0305 (very popular I've learned) not sure why these 2?

*Worth noting: I stated the engine and noticed he was having trouble unlocking the rollup door I shut it off so not to fill the shop with exhaust. Within a few seconds the door started up so i restated the engine and that's when the light came on.
I cleared those 2 codes and they reappeared the next time I drove it.
So is the $$chase on or does the 2 and 5 have a common part fix?
As shown by
Hello everyone, new here.
I'm currently trying out a 2001 TJ. It belongs to a coworker that is as OCD as i am about vehicles.
As i was begining to back out of his shop the engine light came on. He has owned since 2011 and said he'd never seen that light. (I believe him)
My code reader indicates a P0302 & P0305 (very popular I've learned) not sure why these 2?

*Worth noting: I stated the engine and noticed he was having trouble unlocking the rollup door I shut it off so not to fill the shop with exhaust. Within a few seconds the door started up so i restated the engine and that's when the light came on.
I cleared those 2 codes and they reappeared the next time I drove it.
So is the $$chase on or does the 2 and 5 have a common part fix?
Update:
Got the coil pack in and it fixed the problem.

As previously posted by TJ Guru, cylindars 1-6, 2-5 and 3-4 fire together, so a misfire on 2-5 shows the coil that fires 2-5 is failing or arcing out to an easier ground! I have the same problem PLUS a crossover between 2-5 and 1-6. This was caused by original owner never changing the plugs. The TJ now has 110,000 miles. That's a damn long time for ANY spark plug! As that gap increases the high voltage seeks an easier route to ground. I found arc burns around the 3rd coil pack attachment bolt from the front of the engine. I will get a shot of it to show what it looks like.

Hi, I am a new member but not new to jeeps,
I have an oscilloscope, OBD1, OBD2 meter, Vacuum gauge,
compression gauge, Volt ohm meter... etc.

Being an Electronics Engineer for 30 years, I don't throw parts, I verify the parts THEN replace.
I will be changing the timing chain soon as well because anyone who ignores plugs doesn't think about timing chains.

Loose timing chain + slightly warn CAM SENSOR drive assembly = erratic as hell sync timing.
Not healthy for engine or MPG!

I have not done my profile yet so...
2002 TJ 4.0L,
32RH trans,
33" tires,
4" Lift

Waiting for my coil pack to arrive!

back_coil.jpg


Front_closeup.jpg


Front_Coil.jpg
 
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Kawi413p

New Member
Joined
Jan 4, 2020
Messages
11
Location
California
As shown by

Update:
Got the coil pack in and it fixed the problem.

As previously posted by TJ Guru, cylindars 1-6, 2-5 and 3-4 fire together, so a misfire on 2-5 shows the coil that fires 2-5 is failing or arcing out to an easier ground! I have the same problem PLUS a crossover between 2-5 and 1-6. This was caused by original owner never changing the plugs. The TJ now has 110,000 miles. That's a damn long time for ANY spark plug! As that gap increases the high voltage seeks an easier route to ground. I found arc burns around the 3rd coil pack attachment bolt from the front of the engine. I will get a shot of it to show what it looks like.

Hi, I am a new member but not new to jeeps,
I have an oscilloscope, OBD1, OBD2 meter, Vacuum gauge,
compression gauge, Volt ohm meter... etc.

Being an Electronics Engineer for 30 years, I don't throw parts, I verify the parts THEN replace.
I will be changing the timing chain soon as well because anyone who ignores plugs doesn't think about timing chains.

Loose timing chain + slightly warn CAM SENSOR drive assembly = erratic as hell sync timing.
Not healthy for engine or MPG!

I have not done my profile yet so...
2002 TJ 4.0L,
32RH trans,
33" tires,
4" Lift

Waiting for my coil pack to arrive!

View attachment 134375

View attachment 134376

View attachment 134377
Great write up! My Jeep is currently at the stealership. So far they’ve replaced the crank sensor. They were seeing that the rpm signal was being lost supposedly due to the crank sensor (that sensor had been changed 3 times prior. Once with Napa sensor, then junkyard sensor, and then a genuine mopar sensor. They still recommended replacing it and that didn’t solve the issue.

I’m experiencing a 2 and 5 misfire. Originally it was 1 and 6. It changed a couple months ago. The dealership thought the coil boot was allowing it to arc the Napa coil pack had less than 500 miles and less than a year old.I replaced with another Napa coil pack and the dealership is at a standstill.

I bought the Jeep from A shop that bought it from a costumer. Head originally was cracked and shop owner bought it off costumer and did a flip on the vehicle. Put ngk ZFR5plugs Napa coil pack, Napa head and eventually that Napa cranksensor. I’ve had the Jeepsince April 2019 and can’t track down the misfire. I’ve done coolant temperature sensor, cam and crank sensor (mopar parts), another Napa coil pack, cleaned throttle body without with cleaner, vacuum check by blowing cigar smoke into the intake manifold (smoke only came out of where the butterfly valve spring setup is,) compression test
Checked compression (psi)

Dry. Wet

155 205

150 200

145 190

150 208

157 210

155 218

lifters and push rods (a shop I took it to thought an exhaust valve wasn’t fully opening cause the miss.) it had a decent lifter tick.Upon removal of lifter,cylinder 6 lifter was shorter and slightly concave compared to others.

last I heard from the dealership is that even with the new coil pack, their scanner still seems to point towards an issue with it.
 

Kawi413p

New Member
Joined
Jan 4, 2020
Messages
11
Location
California
Great write up! My Jeep is currently at the stealership. So far they’ve replaced the crank sensor. They were seeing that the rpm signal was being lost supposedly due to the crank sensor (that sensor had been changed 3 times prior. Once with Napa sensor, then junkyard sensor, and then a genuine mopar sensor. They still recommended replacing it and that didn’t solve the issue.

I’m experiencing a 2 and 5 misfire. Originally it was 1 and 6. It changed a couple months ago. The dealership thought the coil boot was allowing it to arc the Napa coil pack had less than 500 miles and less than a year old.I replaced with another Napa coil pack and the dealership is at a standstill.

I bought the Jeep from A shop that bought it from a costumer. Head originally was cracked and shop owner bought it off costumer and did a flip on the vehicle. Put ngk ZFR5plugs Napa coil pack, Napa head and eventually that Napa cranksensor. I’ve had the Jeepsince April 2019 and can’t track down the misfire. I’ve done coolant temperature sensor, cam and crank sensor (mopar parts), another Napa coil pack, cleaned throttle body without with cleaner, vacuum check by blowing cigar smoke into the intake manifold (smoke only came out of where the butterfly valve spring setup is,) compression test
Checked compression (psi)

Dry. Wet

155 205

150 200

145 190

150 208

157 210

155 218

lifters and push rods (a shop I took it to thought an exhaust valve wasn’t fully opening cause the miss.) it had a decent lifter tick.Upon removal of lifter,cylinder 6 lifter was shorter and slightly concave compared to others.

last I heard from the dealership is that even with the new coil pack, their scanner still seems to point towards an issue with it.
Jeep has 124k miles
 

Jeepn_Texas

TJ Enthusiast
Joined
Jan 13, 2020
Messages
123
Location
Houston, TX
Great write up! My Jeep is currently at the stealership. So far they’ve replaced the crank sensor. They were seeing that the rpm signal was being lost supposedly due to the crank sensor (that sensor had been changed 3 times prior. Once with Napa sensor, then junkyard sensor, and then a genuine mopar sensor. They still recommended replacing it and that didn’t solve the issue.

I’m experiencing a 2 and 5 misfire. Originally it was 1 and 6. It changed a couple months ago. The dealership thought the coil boot was allowing it to arc the Napa coil pack had less than 500 miles and less than a year old.I replaced with another Napa coil pack and the dealership is at a standstill.

I bought the Jeep from A shop that bought it from a costumer. Head originally was cracked and shop owner bought it off costumer and did a flip on the vehicle. Put ngk ZFR5plugs Napa coil pack, Napa head and eventually that Napa cranksensor. I’ve had the Jeepsince April 2019 and can’t track down the misfire. I’ve done coolant temperature sensor, cam and crank sensor (mopar parts), another Napa coil pack, cleaned throttle body without with cleaner, vacuum check by blowing cigar smoke into the intake manifold (smoke only came out of where the butterfly valve spring setup is,) compression test
Checked compression (psi)

Dry. Wet

155 205

150 200

145 190

150 208

157 210

155 218

lifters and push rods (a shop I took it to thought an exhaust valve wasn’t fully opening cause the miss.) it had a decent lifter tick.Upon removal of lifter,cylinder 6 lifter was shorter and slightly concave compared to others.

last I heard from the dealership is that even with the new coil pack, their scanner still seems to point towards an issue with it.
I would go through the wire harness from the coil pack to the ECU... sounds like you have some chafing that is crossing up the signals and shorting the drivers every now and then. Also, have them check your cam chain... if it has stretched a lot and the Cam Sensor / oil pump drive is warn as well you could have an issue with the cam sensor lagging and causing the ECU to fire wrong plugs. This can explain why higher RPM misfires happen. as RPM increases, the amount of pull on the cam chain increases and Whoop, There it is, Misfire! They should be able to see that on their scope though. I do my own with one of my scopes, here is what I got when checking the timing on my XJ from the Crank sensor to the Cam position sensor... The bottom trace is cam, the upper trace is crank. The cam should always transition in the gap between crank pulses, otherwise, the ECU trigers wrong bank of plugs. Cam should lead at least a little bit as shown here, never the same time or after the crank pulses start.

CAM_CRANK.jpg
 
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Kawi413p

New Member
Joined
Jan 4, 2020
Messages
11
Location
California
I would go through the wire harness from the coil pack to the ECU... sounds like you have some chafing that is crossing up the signals and shorting the drivers every now and then. Also, have them check your cam chain... if it has stretched a lot and the Cam Sensor / oil pump drive is warn as well you could have an issue with the cam sensor lagging and causing the ECU to fire wrong plugs. This can explain why higher RPM misfires happen. as RPM increases, the amount of pull on the cam chain increases and Whoop, There it is, Misfire! They should be able to see that on their scope though. I do my own with one of my scopes, here is what I got when checking the timing on my XJ from the Crank sensor to the Cam position sensor... The bottom trace is cam, the upper trace is crank. The cam should always transition in the gap between crank pulses, otherwise, the ECU trigers wrong bank of plugs. Cam should lead at least a little bit as shown here, never the same time or after the crank pulses start.

View attachment 134406
I really appreciate the time and detail you put in your posts. The pictures and explanations help a lot. I’m expecting a call from them today. I’ll bring it up and also see what else they’ve done in the meantime. I’ll report back later today!
 

ejay

TJ Enthusiast
Joined
Dec 29, 2019
Messages
560
Location
Ventura County, Commiefornia
My God you've had a lot done to track this down with very little success. I'd be pulling my hair out at this point. I'm dealing with a misfire myself. Though mine was originally 1 and 5. Now it's just 1.

In my case I pressure tested the exhaust system, seafoam the vacuum lines and TB, replaced the plugs with iridiums, tested the coils, sound probed the injectors for actuation, used a multimeter on the CPS and injectors, and looked for arcs or wire cuts/breaks to no avail. I'll be replacing the injectors this weekend. If that doesn't solve it, it's on to cylinder compression tests.
 

Jeepn_Texas

TJ Enthusiast
Joined
Jan 13, 2020
Messages
123
Location
Houston, TX
I really appreciate the time and detail you put in your posts. The pictures and explanations help a lot. I’m expecting a call from them today. I’ll bring it up and also see what else they’ve done in the meantime. I’ll report back later today!
My pleasure!
I hope we can get you back on the road quickly!
Jeeplessness sucks!
 

Kawi413p

New Member
Joined
Jan 4, 2020
Messages
11
Location
California
Hey guys. Jeep called this morning. They think it might be warm cam lobes causing the misfire. They had their foreman working on it. They didn’t take anything apart to verify that. He wanted to talk to me first and see if I wanted to spend more money to start diving into it. One of the things they pointed out is that cylinder 5 will miss first then as it gets warmer, it cylinder 2 starts to miss. It might be awhile before I get to this. It sucks becuase I just changed lifters and pushrods this summer. I debated swapping cams but tried to save money. Thanks again for all your help guys. I will follow up however long it takes.