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 June 9th, 2019, 21:50
Chris2552's Avatar
Chris2552 Chris2552 is offline
NAXJA Forum User
 
Join Date: Apr 2019
Location: West Virginia
Posts: 3
Question 98 4.0L Weird idle?

I bought a 1998 Cherokee Classic recently and it's giving me one heck of a headache. The Jeep will idle for a minute, then fall flat on its face. I've replaced the O2 Sensors, IAC, tried a different ECM, plugs and wires, TPS, and the MAP Sensor. I've cleaned a ton of grounds but still no luck. When I check for codes, I get P1391, I've replaced the CPS with 2 off of other jeeps and bought a new one, still no luck. It seems like it has a really bad misfire, but goes away in the higher RPMS. I've checked the fuel pressure and did a compression test, they checked out good. Also checked for vacuum leaks, didn't find any. I've ran out of things to check
Reply With Quote
  #2  
Old June 10th, 2019, 02:53
4x4JeePmaNthINg's Avatar
4x4JeePmaNthINg 4x4JeePmaNthINg is online now
NAXJA Forum User
 
Join Date: Nov 2008
Location: colorado, severance
Posts: 995
Re: 98 4.0L Weird idle?

Timing chain? Distributor gear/shaft play?

Did you test grounds, shorts, signal, supply?
Test cmps, visual inspection as well, RCP on here recently got lucky finding his P1391, just by visually inspecting.


I'm in the same boat kinda, but I haven't replaced sensors yet lol, might find out this week.

I do advise taking it to get a diagnostic for lab scope reading, it's very informative and can point out a lot of issues meters can't.

Also a recent recommendation I've read it take fuel pressure reading under load, might change. Meh


Keep us posted!
Reply With Quote
  #3  
Old June 10th, 2019, 05:32
asymptonic asymptonic is offline
NAXJA Member
 
Join Date: Jul 2012
Location: Austin, Texas
Posts: 199
Re: 98 4.0L Weird idle?

Only hint I see in that is that it idles okay "for a minute". Could it be an issue once the motor warms up and the ECM goes into closed loop?



Do you notice a change at a particular engine temperature or does it die fairly quickly after starting?
__________________
1998 4.0 I6, AX15, NP231
Reply With Quote
  #4  
Old June 10th, 2019, 07:21
Tim_MN's Avatar
Tim_MN Tim_MN is offline
Freakish Hand Strength
 
Join Date: Mar 2003
Location: Minneapolis, MN
Posts: 6,585
Re: 98 4.0L Weird idle?

Solve the P1391 code. I would suspect the Cam sensor synchronization is out to tolerance. A mis-indexed distributor/cam sensor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. The proper indexing procedure must be used as outlined in the service manual.


P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.
*
P1391 – Possible symptoms:
(1) random misfire/stumble/bucking/stalling, often over bumps or right hand turns or when going into reverse.
(2) shorted out the Fuel pump/ECU power wire.

Possible causes
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.
-CMP SENSOR OUT OF SYNC
-DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
-DAMAGED TONE WHEEL/PULSE RING (CAMSHAFT)
-IRREGULAR LAB SCOPE PATTERN OF CMP SIGNAL
-INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
-IRREGULAR LAB SCOPE PATTERN OF CKP SIGNAL
-WIRING HARNESS INTERMITTENT
-INTERMITTENT CMP SIGNAL LOSS WHEN WIRING IS WIGGLED
-CRANKSHAFT POSITION SENSOR CONNECTOR/WIRING
-FAULTY CRANKSHAFT POSITION SENSOR


Potential Fixes:
Fix #1:
Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor. Replace corroded ground wires/connectors and clean ground wire connection points.
Fix #2:*
Timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.
*
Google Scan Tools, O-Scopes and Toothpicks, and read the article.

Read this also : http://www.jeepforum.com/forum/f19/j...e-fix-3487474/

A mis-indexed distributor/cam sensor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. The proper indexing procedure must be used as outlined in the service manual.
__________________
.
.

Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
Reply With Quote
  #5  
Old June 10th, 2019, 09:12
Chris2552's Avatar
Chris2552 Chris2552 is offline
NAXJA Forum User
 
Join Date: Apr 2019
Location: West Virginia
Posts: 3
Re: 98 4.0L Weird idle?

Thank you everyone for the advice! I forgot to mention that the engine has been swapped in the past with a 1996 engine. During inspection, I found a bolt missing and a very loose bolt in the top of the bellhousing. Do you think it would cause the CPS to loose sync when the engine vibrates or moves?
Reply With Quote
  #6  
Old June 12th, 2019, 08:22
denverd1's Avatar
denverd1 denverd1 is offline
NAXJA Member
 
Join Date: Dec 2013
Location: Tyler, TX
Posts: 625
Re: 98 4.0L Weird idle?

CkPS

keep an extra in the glove box
__________________
Chili Pepper '98
4.5" lift, locked on both ends, 33s
10K winch and a lot of skinny pedal
Reply With Quote
  #7  
Old June 12th, 2019, 08:22
denverd1's Avatar
denverd1 denverd1 is offline
NAXJA Member
 
Join Date: Dec 2013
Location: Tyler, TX
Posts: 625
Re: 98 4.0L Weird idle?

Quote:
Originally Posted by Chris2552 View Post
Thank you everyone for the advice! I forgot to mention that the engine has been swapped in the past with a 1996 engine. During inspection, I found a bolt missing and a very loose bolt in the top of the bellhousing. Do you think it would cause the CPS to loose sync when the engine vibrates or moves?
Abso-damn-lutely
__________________
Chili Pepper '98
4.5" lift, locked on both ends, 33s
10K winch and a lot of skinny pedal
Reply With Quote
  #8  
Old June 12th, 2019, 10:19
Tim_MN's Avatar
Tim_MN Tim_MN is offline
Freakish Hand Strength
 
Join Date: Mar 2003
Location: Minneapolis, MN
Posts: 6,585
Re: 98 4.0L Weird idle?

Quote:
Originally Posted by Chris2552 View Post
I found a bolt missing and a very loose bolt in the top of the bellhousing. Do you think it would cause the CPS to loose sync when the engine vibrates or moves?
The AW-4 has 2 locating pins and about 8 bolts. A few loose or missing bolts would be very unlikely have an effect upon the CranKshaft Position Sensor.
__________________
.
.

Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
Reply With Quote
  #9  
Old Today, 21:30
4x4JeePmaNthINg's Avatar
4x4JeePmaNthINg 4x4JeePmaNthINg is online now
NAXJA Forum User
 
Join Date: Nov 2008
Location: colorado, severance
Posts: 995
Re: 98 4.0L Weird idle?

Any luck chris?
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
Weird idle zachandandy OEM Tech Discussion 5 July 12th, 2011 12:17
weird idle tyspier OEM Tech Discussion 4 November 18th, 2007 20:18
weird idle/something else weird. gijosiahh OEM Tech Discussion 2 November 1st, 2007 23:39
Weird Low Idle jeepsrock OEM Tech Discussion 9 May 8th, 2006 22:52
Weird Idle low_life OEM Tech Discussion 13 May 20th, 2004 06:54


All times are GMT -7. The time now is 21:38.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014