NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > OEM Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs.

Reply
 
Thread Tools Display Modes
  #1  
Old August 31st, 2012, 21:52
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Basic Misfire Question

Ok so i have been having a cylinder 4 misfire here for about 2 months now and just can not figure it out. I have a few threads on here about it but just want to start over by asking ---- How does my 2000 XJ even know that a single cylinder is misfiring, its not like there is a sensor on each cylinder thats saying " hey im misfiring " Could there be something telling my ECU that cyl 4 is misfiring but it really isnt? Also if the engine light comes on for whatever reason how long should it take for it to shut off by its self ( given the problem is fixed )?
Reply With Quote
  #2  
Old August 31st, 2012, 22:08
Ecomike's Avatar
Ecomike Ecomike is offline
NAXJA# 2091
 
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 15,333
Re: Basic Misfire Question

The ECU (PCM) counts the time between teeth passing by on the flex plate or flywheel. If the cylinder fires normally the engine rotates faster than if the cylinder miss fires. The late arrival of the tooth past the CPS is how it detects a miss fire.
__________________
Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
Reply With Quote
  #3  
Old August 31st, 2012, 22:21
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

Quote:
Originally Posted by Ecomike View Post
The ECU (PCM) counts the time between teeth passing by on the flex plate or flywheel. If the cylinder fires normally the engine rotates faster than if the cylinder miss fires. The late arrival of the tooth past the CPS is how it detects a miss fire.
Thanks, good info. Any idea about the other part of my question about how long it takes to rest the engine light? Reason for my question is that I thought it was like after 100 miles or something like that. My engine light is always on for this misfire, Today i ran to the store right over the hill, less then a mile and the light started flashing and then it went to limp mode and ran crappy, I left the store and ran fine and came home, was home for a half hr then left and no light for the 30 min drive. was there for a few hrs then left and it started flashing and then running crappy, quick shut off then restart and then fine again...
Reply With Quote
  #4  
Old August 31st, 2012, 22:23
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

how crazy would it be to have had a bad crank sensor, then replace it with a junk after market one and have the same symptoms as the original bad sensor? You would think that even if the second one was bad there would be different symptoms
Reply With Quote
  #5  
Old September 1st, 2012, 04:03
birchlakeXJ's Avatar
birchlakeXJ birchlakeXJ is offline
NAXJA Forum User
 
Join Date: Jan 2008
Location: Melrose, MN
Posts: 2,779
Re: Basic Misfire Question

Quote:
Originally Posted by Dcoy1283 View Post
how crazy would it be to have had a bad crank sensor, then replace it with a junk after market one and have the same symptoms as the original bad sensor? You would think that even if the second one was bad there would be different symptoms
I'm not a fan of aftermarket crank sensors, but if you have the exact same symptoms with both of them, this is not likely to be your problem.
Reply With Quote
  #6  
Old September 1st, 2012, 12:03
Ecomike's Avatar
Ecomike Ecomike is offline
NAXJA# 2091
 
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 15,333
Re: Basic Misfire Question

A bad crank sensor would not sense a missfire. You have a missfire. Now you need to determine why. When it blinks the CEO light, you have a dangerous missfire, the kind that can damage the engine! When it suddenly runs rough and stops flashing, that means the computer has turned off the fuel injector, until you restart the engine to avoid serious engine damage!!!!

Possible causes:

Bad valve
Bad Valve seal
Bad spark plug (even if it is new)
Bad Plug wire
Bad Cap on that pin, #4
Bad, or dirty, leaking, or sticking fuel injector
cracked head (hairline line crack with no other symptoms than a missfire, YET!)
Loss of compression, bad piston, or piston rings....

Bad wiring or connectors in that fuel injector wire circuit.

Hair line head crack is a real possibility, as is a bad spark plug (even if it is new, or a bad plug wire). Sticking fuel injector, partially plugged....is possible too.

The 2000 heads are notorious for head cracks, the 0331 casting!!!
__________________
Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091

Last edited by Ecomike; September 1st, 2012 at 12:07.
Reply With Quote
  #7  
Old September 1st, 2012, 21:05
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

Quote:
Originally Posted by Ecomike View Post
A bad crank sensor would not sense a missfire. You have a missfire. Now you need to determine why. When it blinks the CEO light, you have a dangerous missfire, the kind that can damage the engine! When it suddenly runs rough and stops flashing, that means the computer has turned off the fuel injector, until you restart the engine to avoid serious engine damage!!!!

Possible causes:

Bad valve
Bad Valve seal
Bad spark plug (even if it is new)
Bad Plug wire
Bad Cap on that pin, #4
Bad, or dirty, leaking, or sticking fuel injector
cracked head (hairline line crack with no other symptoms than a missfire, YET!)
Loss of compression, bad piston, or piston rings....

Bad wiring or connectors in that fuel injector wire circuit.

Hair line head crack is a real possibility, as is a bad spark plug (even if it is new, or a bad plug wire). Sticking fuel injector, partially plugged....is possible too.

The 2000 heads are notorious for head cracks, the 0331 casting!!!

I just have a hard time understanding how it could mechanical it it only happens sometimes. Today I ran around getting some things ready and it did the normal thing and I restarted it then went home.... 1/2 hr later I left again and the cel light went off and stayed off for a 200 mile trip I went on. Ran great going up some PA mountains, then I stoped at a store 1/2 hr from my house for about an hr then got in and it started flashing and missing.... restart and then fine. Thing is just crazy and runs great 90% of the time.
Reply With Quote
  #8  
Old September 1st, 2012, 21:21
Ecomike's Avatar
Ecomike Ecomike is offline
NAXJA# 2091
 
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 15,333
Re: Basic Misfire Question

A lot of things change as it cools and heats up, lots of cycling, and non-constant stuff going on. Cylinder misfires are actually common, but the PCM counts the number of misfires and at some point if there are too many misfires as a ratio of total compression strokes, then it sets the CEL. If it gets really out of whack it flashes the light and turns off that fuel injector to protect the piston wall from getting washed with gas and scored up badly and to protect the Cat converter from overheating damage.

The computer is trying to tell you to find and fix a small problem before it damages the entire engine beyond repair!!! It could just be a sticking fuel injector or bad spark plug, or bad spark coil that is not firing right every time. Or there is a hair line crack in the head, that opens up when cold, seals when hot, but that will only get worse if you don't fix it now!!!
__________________
Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091

Last edited by Ecomike; September 1st, 2012 at 21:30.
Reply With Quote
  #9  
Old September 3rd, 2012, 22:39
Wlahey Wlahey is offline
NAXJA Forum User
 
Join Date: Nov 2006
Location: New Orleans
Posts: 13
Re: Basic Misfire Question

Did you have any other codes. It sounds similar to my problem, but mine begins to misfire and sputter after about twenty minutes, and it does it everytime. I turn the ignition off and back on and it clears for a little while. I am also getiting loss of Camshaft Crank signal code. I replaced both sensors and checked wiring harness still have the same problem. Jeep runs great, while it runs...
Reply With Quote
  #10  
Old September 4th, 2012, 08:28
yossarian19's Avatar
yossarian19 yossarian19 is offline
NAXJA Forum User
 
Join Date: Mar 2007
Location: Grass Valley, CA
Posts: 3,480
Re: Basic Misfire Question

Remove and inspect all of the plugs. Look for differences between your #4 plug and all the others. If it is light, it is lean. If it is dark, probably rich - or oil fouled.
Check your spark distribution.
Etc.
basically - don't argue with the CEL, you really do have a problem in the engine, start pulling & inspecting things and report your findings. We'll help you narrow it down to the cause.
Reply With Quote
  #11  
Old September 5th, 2012, 17:45
offroadordnance offroadordnance is offline
NAXJA Forum User
 
Join Date: Jul 2011
Location: Florida
Posts: 241
Re: Basic Misfire Question

If a lifter is slightly pumped up/sticking lifter or a weak spring bouncing on it's seat you will lose compression. Little or no compression is impossible to ignite and will cause a misfire. Misfire is unburned fuel washing your cylinder walls, diluting the oil, and causing "catalyst damaging misfires", blinking CEL. Did you try a low visc oil to eliminate the possibilty of pumped/sticky lifter or replace the valve springs?
Reply With Quote
  #12  
Old September 6th, 2012, 19:58
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

Quote:
Originally Posted by offroadordnance View Post
If a lifter is slightly pumped up/sticking lifter or a weak spring bouncing on it's seat you will lose compression. Little or no compression is impossible to ignite and will cause a misfire. Misfire is unburned fuel washing your cylinder walls, diluting the oil, and causing "catalyst damaging misfires", blinking CEL. Did you try a low visc oil to eliminate the possibilty of pumped/sticky lifter or replace the valve springs?
Its worth a try, what weight would you recomend trying?..... Thanks and I took the valve cover off and inspected everything. It looked brand new and everything was tight, figured so being its a 2005 jasper engine so it should have well under 100k on it. I do understand that I cant see a week spring and should just replace the ones on #4 to see what happens but to be honest Im not 100% positve on how to replace the valve springs.

Last edited by Dcoy1283; September 6th, 2012 at 20:08.
Reply With Quote
  #13  
Old September 6th, 2012, 20:00
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

Quote:
Originally Posted by yossarian19 View Post
Remove and inspect all of the plugs. Look for differences between your #4 plug and all the others. If it is light, it is lean. If it is dark, probably rich - or oil fouled.
Check your spark distribution.
Etc.
basically - don't argue with the CEL, you really do have a problem in the engine, start pulling & inspecting things and report your findings. We'll help you narrow it down to the cause.
They all look the same, I replaced them with champion copper cores then swapped them around a few times then tried the NGK plugs and same results....... P0304...... this number haunts my dreams
Reply With Quote
  #14  
Old September 6th, 2012, 20:04
Dcoy1283 Dcoy1283 is offline
NAXJA Forum User
 
Join Date: Jul 2012
Location: Apollo, PA
Posts: 70
Re: Basic Misfire Question

Quote:
Originally Posted by Wlahey View Post
Did you have any other codes. It sounds similar to my problem, but mine begins to misfire and sputter after about twenty minutes, and it does it everytime. I turn the ignition off and back on and it clears for a little while. I am also getiting loss of Camshaft Crank signal code. I replaced both sensors and checked wiring harness still have the same problem. Jeep runs great, while it runs...
The only code that im getting is the P0304. When this all started back in july I was getting an evap code also but found and fixed it back between the tank and the canister. For some strange reason turning my ac on or putting it in neutral and keeping the rpms up to 1.5-2k I can prevent it from doing it. Mine happens almost everyday within a mile from leaving somewhere and the CEL flashes here and there when Im driving but doesnt mis
Reply With Quote
  #15  
Old September 6th, 2012, 21:10
offroadordnance offroadordnance is offline
NAXJA Forum User
 
Join Date: Jul 2011
Location: Florida
Posts: 241
Re: Basic Misfire Question

Quote:
Originally Posted by Dcoy1283 View Post
Its worth a try, what weight would you recomend trying?..... Thanks and I took the valve cover off and inspected everything. It looked brand new and everything was tight, figured so being its a 2005 jasper engine so it should have well under 100k on it. I do understand that I cant see a week spring and should just replace the ones on #4 to see what happens but to be honest Im not 100% positve on how to replace the valve springs.
From your other posts, it only happens when it's cold? I'd put 5w-30 in it for a hundred miles or so and see if the cold misfire goes away. The thinner oil will help clean any sludge or varnish out which isnt a bad thing

If its a spring you won't know until you swap them out.

Here's a good link that explains more about how springs/lifters can cause misfires. http://www.cranecams.com/faqview.php?s_id=33
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Basic 242 Question AL BUNDY OEM Tech Discussion 5 May 1st, 2009 10:49
Basic question xringx OEM Tech Discussion 7 July 18th, 2006 14:45
Basic Tech Question...Thread Cleaning Yucca-Man OEM Tech Discussion 6 September 30th, 2005 07:44
Basic 4WD Question Timber OEM Tech Discussion 4 July 19th, 2005 13:59
basic question about leaf springs-- lapaul Modified Tech Discussion 2 October 15th, 2004 14:39


All times are GMT -7. The time now is 04:56.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014