Cylinder 6 misfire?
08-04-2010 | 12:51 PM
#46
CF Veteran
Joined: Jul 2009
Posts: 1,640
Likes: 0
From: Keesler AFB, MS
Year: 1998 XJ
Model: Cherokee
Engine: 4.0L
Update on my Misfire
First off i wouldnt buy a new injector, just swap number 5 and 6 and see if the problem moves to cylinder 5
Now i removed my head the other day and found out i had atleast two cracks in my head. Cylinder 1, my problem cylinder was the worst. It cracked right in between the two valve seats. cylinder 2 had a crack but wasn't affecting anything yet. I had to buy a new referb'd head and it runs great now. no more idleing like crap
Now i removed my head the other day and found out i had atleast two cracks in my head. Cylinder 1, my problem cylinder was the worst. It cracked right in between the two valve seats. cylinder 2 had a crack but wasn't affecting anything yet. I had to buy a new referb'd head and it runs great now. no more idleing like crap
08-04-2010 | 09:10 PM
#47
Thread Starter
Member
Joined: Apr 2010
Posts: 170
Likes: 0
Model: Cherokee
First off i wouldnt buy a new injector, just swap number 5 and 6 and see if the problem moves to cylinder 5
Now i removed my head the other day and found out i had atleast two cracks in my head. Cylinder 1, my problem cylinder was the worst. It cracked right in between the two valve seats. cylinder 2 had a crack but wasn't affecting anything yet. I had to buy a new referb'd head and it runs great now. no more idleing like crap
Now i removed my head the other day and found out i had atleast two cracks in my head. Cylinder 1, my problem cylinder was the worst. It cracked right in between the two valve seats. cylinder 2 had a crack but wasn't affecting anything yet. I had to buy a new referb'd head and it runs great now. no more idleing like crap
08-05-2010 | 07:51 AM
#48
CF Veteran
Joined: Jul 2009
Posts: 1,640
Likes: 0
From: Keesler AFB, MS
Year: 1998 XJ
Model: Cherokee
Engine: 4.0L
08-07-2010 | 06:39 PM
#49
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Member
Joined: Apr 2010
Posts: 170
Likes: 0
Model: Cherokee
Update
Compression Test showed as follows:
Cylinder #1: 95psi
#2: 115psi
#3: 105psi
#4: 100psi
#5: 105psi
#6: (the misfire one) 105psi
A little low, but still within optimal specs I think. Opinions??
Also had a coolant system pressure checked as there was apparent coolant traces showing on #1 Spark plug which would seem I might have a head gasket crack and would explain why I'm losing coolant(1 gallon about every 5 weeks) but coolant pressure check came up with no leaks.
So, I then took it to the dealership for a block test, and it came up fine as well. I might have a hairline crack in the head I guess, but it doesn't seem to be a huge problem yet since everything else has checked out ok. I bought a stop leak tablet for the radiator(about to put in, when it cools) to see if that will seal up the leak. I'll keep everyone updated. Any thoughts as to why I would get this sporadic cylinder 6 misfire now?
Cylinder #1: 95psi
#2: 115psi
#3: 105psi
#4: 100psi
#5: 105psi
#6: (the misfire one) 105psi
A little low, but still within optimal specs I think. Opinions??
Also had a coolant system pressure checked as there was apparent coolant traces showing on #1 Spark plug which would seem I might have a head gasket crack and would explain why I'm losing coolant(1 gallon about every 5 weeks) but coolant pressure check came up with no leaks.
So, I then took it to the dealership for a block test, and it came up fine as well. I might have a hairline crack in the head I guess, but it doesn't seem to be a huge problem yet since everything else has checked out ok. I bought a stop leak tablet for the radiator(about to put in, when it cools) to see if that will seal up the leak. I'll keep everyone updated. Any thoughts as to why I would get this sporadic cylinder 6 misfire now?
08-08-2010 | 08:21 PM
#50
Newbie
Joined: Aug 2010
Posts: 1
Likes: 0
Model: Cherokee
I have been having this same issue for about a year and half. This is the first thread I have seen with people having the check engine light and rough idle after having high rpms. My magic number is 3000 rpms. I put through Lucas no leak additive, and it has seemed to calm it down a little bit but has not solved the problem yet. My error code is cylinder 1 misfire. Jeep '99 Cherokee Classic 4.0L
08-08-2010 | 10:36 PM
#51
Member
Joined: Jun 2010
Posts: 155
Likes: 1
From: Easthampton, MA
Year: 1999
Model: Cherokee
Engine: 4.0
Full can of Seafoam in every full tank for the last month has done wonders for my idle, also heat taped my whole fuel line and all 6 injectors. YET, even when mine seems to be idling ok, I still get a random cyl 1 misfire. I clear it, and within a few trips it will return, Very friggin annoying. In the next few months I am going to replace the head, and exhaust manifold(crack). I'm just waiting for it to cool off down here, way too hot and miserable to do the job right now.
08-09-2010 | 08:12 PM
#52
Junior Member
Joined: Aug 2009
Posts: 30
Likes: 0
Year: 1998
Model: Cherokee
Engine: 4.0
I get that on my 98. It starts out as mis in 1 the goes to 3 and 6. Only happens on a drive of 20 miles or more on the highway. If you see the TSB it also mentions something about vibrations. By the way I have a new engine, plugs, injectors, wires, rotor, cap. I don't know how I could get enough carbon buildup in 500 miles but who knows. I bought a can of the cleaner from the dealership and it worked for a month before it came back on. But off now. ???????
08-14-2010 | 10:09 PM
#53
Member
Joined: Jun 2010
Posts: 155
Likes: 1
From: Easthampton, MA
Year: 1999
Model: Cherokee
Engine: 4.0
Update to my misfire issue.
On my 4th can of seafoam at fill up. I have eliminated about 80% of my misfire and rough idle. It is way better than when I first got my xj a couple months back. I also switched to mid grade gas and it has helped a lot too. I think the carbon is going bye bye on my valves.
On my 4th can of seafoam at fill up. I have eliminated about 80% of my misfire and rough idle. It is way better than when I first got my xj a couple months back. I also switched to mid grade gas and it has helped a lot too. I think the carbon is going bye bye on my valves.
08-23-2010 | 04:17 PM
#55
Member
Joined: Jun 2010
Posts: 155
Likes: 1
From: Easthampton, MA
Year: 1999
Model: Cherokee
Engine: 4.0
Mine are spot on perfectly gapped, I rechecked them after I put the new ones in. It has been doing this idle thing since my mother bought it 2 years ago. I am 99.9% sure it is a bad valve. Sometimes it idles good, more than 50% it idles like crap. It will idle good cold one day, crappy next, good when at normal temp one day, bad the next. Pretty sure there is a bad exhaust valve since it sucks paper into the tailpipe. Sometimes it will idle with a miss that feels like a cylinder is not firing at all. The next day it is fine, it's pretty annoying.
10-27-2010 | 12:14 PM
#56
Junior Member
Joined: Oct 2010
Posts: 31
Likes: 0
From: DFW
Year: 2001
Model: Cherokee
Engine: 4.0
Hi all 
2001 Sport here, <89000 miles with P0306 cylinder 6 misfire code that will not go away -
- 6 new plugs - no effect
- 1 new coil pack - no effect
- 1 new electronic module for spark control - no effect
- 1 new air filter - no effect
- swapped #5 & #6 fuel injectors - no effect;
- noid light in all injector connectors show good firing (but not necessarily good voltage/timing!)
- cleaned throttle body with throttle body/map cleaner - no effect
- made sure injectors were angled to the 2 o'clock position - no effect
- disconnecting the injector connectors one at a time resulted in engine changes, except for when disconnecting injector #6 connector (hence the misfire code?)
+/- Found a vacuum leak on the brake booster - the plastic plug-in on the booster had a crack in it; replaced it and engine became smoother, but P0306 still happens, i.e. no effect.
+ Fuel pressure holds steady at 45 psi - more to follow in #8 below...
+ compression check - leak down and compression are ok
1. Will put in new crankshaft position sensor tonight
if no effect then
2. Use 1 bottle of SeaFoam (2nd bottle on hand too :P )
if no effect then
3. Replace IAC valve
if no effect then
4. Rotate valves on cylinder #6
if no effect then
5. R/R intake/exhaust manifold gasket (possible leak?)
if no effect then
6. Check intake manifold for cracks
if no effect then
7. thermal protection wrap the injectors
if no effect then
8. Disconnect and flush the fuel rail and check results.Why? The injector fuel rail sits at an angle where the #1 is higher than the #6; possible collection of rust/crud at the lower #6 end in the fuel rail causing insufficient fuel flow to #6 injector? Since there is no fuel return line, this could be valid.
if no effect then
9. regap #6 plug to slightly larger than .035
if no effect then
10. ?what now? (replace all injectors? new exhaust? new head? new engine?)
(btw, I'm gonna start a new thread with my issues later tonight)
2001 Sport here, <89000 miles with P0306 cylinder 6 misfire code that will not go away -
- 6 new plugs - no effect
- 1 new coil pack - no effect
- 1 new electronic module for spark control - no effect
- 1 new air filter - no effect
- swapped #5 & #6 fuel injectors - no effect;
- noid light in all injector connectors show good firing (but not necessarily good voltage/timing!)
- cleaned throttle body with throttle body/map cleaner - no effect
- made sure injectors were angled to the 2 o'clock position - no effect
- disconnecting the injector connectors one at a time resulted in engine changes, except for when disconnecting injector #6 connector (hence the misfire code?)
+/- Found a vacuum leak on the brake booster - the plastic plug-in on the booster had a crack in it; replaced it and engine became smoother, but P0306 still happens, i.e. no effect.
+ Fuel pressure holds steady at 45 psi - more to follow in #8 below...
+ compression check - leak down and compression are ok
1. Will put in new crankshaft position sensor tonight
if no effect then
2. Use 1 bottle of SeaFoam (2nd bottle on hand too :P )
if no effect then
3. Replace IAC valve
if no effect then
4. Rotate valves on cylinder #6
if no effect then
5. R/R intake/exhaust manifold gasket (possible leak?)
if no effect then
6. Check intake manifold for cracks
if no effect then
7. thermal protection wrap the injectors
if no effect then
8. Disconnect and flush the fuel rail and check results.Why? The injector fuel rail sits at an angle where the #1 is higher than the #6; possible collection of rust/crud at the lower #6 end in the fuel rail causing insufficient fuel flow to #6 injector? Since there is no fuel return line, this could be valid.
if no effect then
9. regap #6 plug to slightly larger than .035
if no effect then
10. ?what now? (replace all injectors? new exhaust? new head? new engine?)
(btw, I'm gonna start a new thread with my issues later tonight)
10-27-2010 | 12:46 PM
#57
CF Veteran
Joined: Jul 2009
Posts: 1,640
Likes: 0
From: Keesler AFB, MS
Year: 1998 XJ
Model: Cherokee
Engine: 4.0L
Hi all
2001 Sport here, <89000 miles with P0306 cylinder 6 misfire code that will not go away -
- 6 new plugs - no effect
- 1 new coil pack - no effect
- 1 new electronic module for spark control - no effect
- 1 new air filter - no effect
- swapped #5 & #6 fuel injectors - no effect;
- noid light in all injector connectors show good firing (but not necessarily good voltage/timing!)
- cleaned throttle body with throttle body/map cleaner - no effect
- made sure injectors were angled to the 2 o'clock position - no effect
- disconnecting the injector connectors one at a time resulted in engine changes, except for when disconnecting injector #6 connector (hence the misfire code?)
+/- Found a vacuum leak on the brake booster - the plastic plug-in on the booster had a crack in it; replaced it and engine became smoother, but P0306 still happens, i.e. no effect.
+ Fuel pressure holds steady at 45 psi - more to follow in #8 below...
+ compression check - leak down and compression are ok
1. Will put in new crankshaft position sensor tonight
if no effect then
2. Use 1 bottle of SeaFoam (2nd bottle on hand too :P )
if no effect then
3. Replace IAC valve
if no effect then
4. Rotate valves on cylinder #6
if no effect then
5. R/R intake/exhaust manifold gasket (possible leak?)
if no effect then
6. Check intake manifold for cracks
if no effect then
7. thermal protection wrap the injectors
if no effect then
8. Disconnect and flush the fuel rail and check results.Why? The injector fuel rail sits at an angle where the #1 is higher than the #6; possible collection of rust/crud at the lower #6 end in the fuel rail causing insufficient fuel flow to #6 injector? Since there is no fuel return line, this could be valid.
if no effect then
9. regap #6 plug to slightly larger than .035
if no effect then
10. ?what now? (replace all injectors? new exhaust? new head? new engine?)
(btw, I'm gonna start a new thread with my issues later tonight)
2001 Sport here, <89000 miles with P0306 cylinder 6 misfire code that will not go away -
- 6 new plugs - no effect
- 1 new coil pack - no effect
- 1 new electronic module for spark control - no effect
- 1 new air filter - no effect
- swapped #5 & #6 fuel injectors - no effect;
- noid light in all injector connectors show good firing (but not necessarily good voltage/timing!)
- cleaned throttle body with throttle body/map cleaner - no effect
- made sure injectors were angled to the 2 o'clock position - no effect
- disconnecting the injector connectors one at a time resulted in engine changes, except for when disconnecting injector #6 connector (hence the misfire code?)
+/- Found a vacuum leak on the brake booster - the plastic plug-in on the booster had a crack in it; replaced it and engine became smoother, but P0306 still happens, i.e. no effect.
+ Fuel pressure holds steady at 45 psi - more to follow in #8 below...
+ compression check - leak down and compression are ok
1. Will put in new crankshaft position sensor tonight
if no effect then
2. Use 1 bottle of SeaFoam (2nd bottle on hand too :P )
if no effect then
3. Replace IAC valve
if no effect then
4. Rotate valves on cylinder #6
if no effect then
5. R/R intake/exhaust manifold gasket (possible leak?)
if no effect then
6. Check intake manifold for cracks
if no effect then
7. thermal protection wrap the injectors
if no effect then
8. Disconnect and flush the fuel rail and check results.Why? The injector fuel rail sits at an angle where the #1 is higher than the #6; possible collection of rust/crud at the lower #6 end in the fuel rail causing insufficient fuel flow to #6 injector? Since there is no fuel return line, this could be valid.
if no effect then
9. regap #6 plug to slightly larger than .035
if no effect then
10. ?what now? (replace all injectors? new exhaust? new head? new engine?)
(btw, I'm gonna start a new thread with my issues later tonight)
10-27-2010 | 01:41 PM
#58
Junior Member
Joined: Oct 2010
Posts: 31
Likes: 0
From: DFW
Year: 2001
Model: Cherokee
Engine: 4.0
heh, not "looking" for anything. 
Seeing how these misfire conditions seem to plague many owners and seeing many other forums with the same type of threads that say "...will post more when I figure it out..." (and don't give closure) , I thought that my detailed troubleshooting might help those still having similar problems.
I'm not looking for any specific help *yet* as I still have troubleshooting steps left to perform. When I run out of ideas, I may ask for help then.
I have read many, many, many... etc threads on these problems (yes, using the search functions and goooooogle)... just trying to help the community.
Seeing how these misfire conditions seem to plague many owners and seeing many other forums with the same type of threads that say "...will post more when I figure it out..." (and don't give closure) , I thought that my detailed troubleshooting might help those still having similar problems.
I'm not looking for any specific help *yet* as I still have troubleshooting steps left to perform. When I run out of ideas, I may ask for help then.
I have read many, many, many... etc threads on these problems (yes, using the search functions and goooooogle)... just trying to help the community.
10-27-2010 | 02:40 PM
#59
CF Veteran
Joined: Jul 2009
Posts: 1,640
Likes: 0
From: Keesler AFB, MS
Year: 1998 XJ
Model: Cherokee
Engine: 4.0L
heh, not "looking" for anything.
Seeing how these misfire conditions seem to plague many owners and seeing many other forums with the same type of threads that say "...will post more when I figure it out..." (and don't give closure) , I thought that my detailed troubleshooting might help those still having similar problems.
I'm not looking for any specific help *yet* as I still have troubleshooting steps left to perform. When I run out of ideas, I may ask for help then.
I have read many, many, many... etc threads on these problems (yes, using the search functions and goooooogle)... just trying to help the community.
Seeing how these misfire conditions seem to plague many owners and seeing many other forums with the same type of threads that say "...will post more when I figure it out..." (and don't give closure) , I thought that my detailed troubleshooting might help those still having similar problems.
I'm not looking for any specific help *yet* as I still have troubleshooting steps left to perform. When I run out of ideas, I may ask for help then.
I have read many, many, many... etc threads on these problems (yes, using the search functions and goooooogle)... just trying to help the community.
I actually see where you stated you would start a new thread later tonight. I was going off what step 10 said.
10-21-2012 | 07:37 PM
#60
Newbie
Joined: Oct 2012
Posts: 2
Likes: 0
Model: Cherokee
cylinder 1 and 6 misfire??
i also have a simalar problem,1 and 6 is not firing and it all started on a cold morning when i went to crank it,it started up then shut right off so i hit the key again and it started but check engine light was on and was running rough really rough,so i changed coil packs 6 times and still the same problem,i have a code of P0351???? any suggestions as to what this problem might be??
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