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 September 23rd, 2017, 10:53
xjalfh xjalfh is offline
NAXJA Member
 
Join Date: Mar 2011
Location: NE
Posts: 6
Question Momentary rough running about 1 minute after a warm start.

98 XJ with 4.0L.

This problem started out as occasional and only at higher temps, but has increased in frequency over the last year or so to where it now happens every time.

It will start fine in any temperature, but when warm (mid 80s or higher ambient, or if engine is still warm from previously running) about 1 minute after starting it will run really, really rough for about 5-15 seconds. Nearly zero power, stumbles and sputters, popping in the exhaust. Going WOT will cause it to fall flat on its face and nearly stall, while pedalling it between 0-50% throttle seems to bring it out of stumbling more quickly. That could just be coincidence, though.

When it comes back out of it, the engine will continue to run just fine until it is shut of and restarted again (although it may be down just a little on power for a minute or so after the stumble).

A bit dangerous, as it's acting up is timed to occur just as you'd be pulling out into traffic from a parking lot for example.

No codes. I've done some shotgunning. Throttle body cleaned. IAC was cleaned, then replaced. TPS replaced. Exhaust, including O2 sensors were new 6 years ago, but I've since replaced both O2 sensors again (NGK). Front one was completely covered in carbon. Understandable, I suppose, as it tends to pop in the exhaust when it is acting up (fuel, but no spark? excessive fuel with or without spark?).

This is a WAG, but the timing of the problem seems to possibly indicate something going funky when the system is switching from an open-loop starting mode to a closed-loop running mode. I honestly don't even know if/when that occurs.

I've found numerous threads on rough running being caused by a number of issues, but nothing this temporary.

Any suggestions?

Thanks.
Reply With Quote
  #2  
Old September 23rd, 2017, 14:24
trippled trippled is offline
NAXJA Member
 
Join Date: Apr 2006
Location: colorado springs, co
Posts: 1,631
Re: Momentary rough running about 1 minute after a warm start.

Man as soon as started reading I was gonna say the o2 as the woman's 99 did just that but on a cold start and a new o2 fixed it. Any access to live data? With no codes I think that's going to be pretty critical. Checked fuel pressure during the concern?
Reply With Quote
  #3  
Old September 23rd, 2017, 16:53
md21722 md21722 is offline
NAXJA Member
 
Join Date: Feb 2014
Location: Colorado Springs
Posts: 2,294
Re: Momentary rough running about 1 minute after a warm start.

The system goes open loop under many conditions such as heavy throttle. I would consider checking or replacing the crank sensor and don't rule out a bad coil, in addition to what Trippled said.

Last edited by md21722; September 23rd, 2017 at 16:56.
Reply With Quote
  #4  
Old September 23rd, 2017, 17:19
Tim_MN's Avatar
Tim_MN Tim_MN is offline
Freakish Hand Strength
 
Join Date: Mar 2003
Location: Minneapolis, MN
Posts: 5,940
Re: Momentary rough running about 1 minute after a warm start.

Are all of the tune-up parts fresh ?

What are your most recent gas MPG's, and how do they related to your historical MPG's ?

The symptoms described are not typical CPS failure symptoms, cross it off the list. The coil should be tested, but the symptoms are not typical coil failure symptoms.

I would start with fuel pressure testing, being sure to closely monitor the pressure while the symptoms occur. Leave the pressure tester in-line and test for fuel pump check valve failure also. I would test the Coolant Temperature Sensor also.

The onset of the symptoms really does suggest an issue when the PCM switches from cold start open loop to closed loop operation. Bucking, backfiring, and stalling should make O2 sensor issues the first thing to suspect. Check the O2 sensor heater fuses, visually inspect the O2 sensor wire harness for damaged wires and chafed/melted wire insulation, inspect the O2 sensor plugs for corrosion and pushed back wire pins, and test the O2 sensor wires for continuity. If the O2 sensors were not practically new, I would have suggested testing them as well.
__________________
.
.

Quote:
Originally Posted by bimmerjeeper

Blanket caught in the rear liftgate latch. Now I can't open.
.

Last edited by Tim_MN; September 23rd, 2017 at 17:29.
Reply With Quote
  #5  
Old September 23rd, 2017, 19:01
Green XJ Jeep Green XJ Jeep is offline
NAXJA Member 4950
 
Join Date: Mar 2011
Location: Spanaway Wa
Posts: 525
Re: Momentary rough running about 1 minute after a warm start.

I would suspect the temp sensor
Reply With Quote
  #6  
Old September 23rd, 2017, 20:08
xjalfh xjalfh is offline
NAXJA Member
 
Join Date: Mar 2011
Location: NE
Posts: 6
Re: Momentary rough running about 1 minute after a warm start.

I got the vehicle about 6 years ago. At that time I replaced the coil, cap, wires, plugs. So that's all the fresher the tuneup parts are.

I replaced the fuel pump module about 4 months ago (Bosch) due to hard starts (check valve). Replacing the pump didn't seem to have any affect good or bad on the problem at hand at that time.

I'll have to find me a fuel pressure gauge anyway.

I now have access to an odb scanner that does recording, but of course it rained this afternoon so it was too cool and it didn't act up. I tried recording anyway just to test it out and the scan tool appears to only record a set of readings every 5 seconds. It may end up being useless for this problem. I'll give it a shot tomorrow though.

There aren't any readily apparent problems with the O2 wiring harnesses, and the heater fuse is good. I'll have to dig more into the O2 harness. About the only thing I've done as far as wiring is concerned is to clean, and reseat the connectors on the PCM.

If I'm lucky, I'll be able to capture some obviously funky readings tomorrow, maybe temps or O2 readings, or???, but at one reading every 5 seconds it might be difficult.

Any recommendations for an obdii device, even one that requires a laptop, or smart phone, that can do more continuous recording?
Reply With Quote
  #7  
Old September 24th, 2017, 17:52
HobHayward HobHayward is offline
NAXJA Forum User
 
Join Date: Oct 2013
Location: MA
Posts: 17
Re: Momentary rough running about 1 minute after a warm start.

A bad rotor/cap led to stumbling right after a warm start for me. Otherwise it ran pretty much fine. It was pretty weird.
Reply With Quote
  #8  
Old September 24th, 2017, 18:42
The1AndOnlyBug The1AndOnlyBug is offline
NAXJA Forum User
 
Join Date: May 2013
Location: Denver, Co
Posts: 25
Re: Momentary rough running about 1 minute after a warm start.

Quote:
Originally Posted by xjalfh View Post
98 XJ with 4.0L.

This problem started out as occasional and only at higher temps, but has increased in frequency over the last year or so to where it now happens every time.

It will start fine in any temperature, but when warm (mid 80s or higher ambient, or if engine is still warm from previously running) about 1 minute after starting it will run really, really rough for about 5-15 seconds. Nearly zero power, stumbles and sputters, popping in the exhaust. Going WOT will cause it to fall flat on its face and nearly stall, while pedalling it between 0-50% throttle seems to bring it out of stumbling more quickly. That could just be coincidence, though.

When it comes back out of it, the engine will continue to run just fine until it is shut of and restarted again (although it may be down just a little on power for a minute or so after the stumble).

A bit dangerous, as it's acting up is timed to occur just as you'd be pulling out into traffic from a parking lot for example.

No codes. I've done some shotgunning. Throttle body cleaned. IAC was cleaned, then replaced. TPS replaced. Exhaust, including O2 sensors were new 6 years ago, but I've since replaced both O2 sensors again (NGK). Front one was completely covered in carbon. Understandable, I suppose, as it tends to pop in the exhaust when it is acting up (fuel, but no spark? excessive fuel with or without spark?).

This is a WAG, but the timing of the problem seems to possibly indicate something going funky when the system is switching from an open-loop starting mode to a closed-loop running mode. I honestly don't even know if/when that occurs.

I've found numerous threads on rough running being caused by a number of issues, but nothing this temporary.

Any suggestions?

Thanks.
IMO the highlighted to me sounds like heatsoak.
Reply With Quote
  #9  
Old September 25th, 2017, 18:25
xjalfh xjalfh is offline
NAXJA Member
 
Join Date: Mar 2011
Location: NE
Posts: 6
Re: Momentary rough running about 1 minute after a warm start.

I had a fairly lengthy reply that somehow never made it to the thread.

Anyway, thanks for the input.

The cap/rotor/coil/wires were all replaced when I bought the xj about 5 years ago. Strong white spark and the parts all look good.

Sensor heater fuse is good, and the wiring shows no apparent damage. I'll definitely have to look at the O2 wiring much more closely. Squirrels did do a number on the cooling fan wiring once. I remember it throwing a code last winter when it was just idling to warm up. It was related to the front O2 sensor but I don't remember the exact code, and once it was cleared it never returned.

The odb scanner I have does have a record function, but it only records readings every 5 seconds. I ordered a new one that connects to a laptop/phone, so hopefully I'll capture something helpful in the next few days.
Reply With Quote
  #10  
Old October 6th, 2017, 02:37
smac999 smac999 is offline
NAXJA Forum User
 
Join Date: Feb 2005
Location: Vancouver, Can
Posts: 9
Re: Momentary rough running about 1 minute after a warm start.

my 99 was doing exact same thing a few years ago. 02 fixed it
Reply With Quote
  #11  
Old October 6th, 2017, 02:39
smac999 smac999 is offline
NAXJA Forum User
 
Join Date: Feb 2005
Location: Vancouver, Can
Posts: 9
Re: Momentary rough running about 1 minute after a warm start.

Quote:
Originally Posted by The1AndOnlyBug View Post
IMO the highlighted to me sounds like heatsoak.
heat soak causes no start or bad running right at start.
Reply With Quote
  #12  
Old October 7th, 2017, 07:21
cruiser54's Avatar
cruiser54 cruiser54 is offline
NAXJA Forum User
 
Join Date: Nov 2009
Location: Prescott, Az
Posts: 6,261
Re: Momentary rough running about 1 minute after a warm start.

I wonder if you have an injector or 2 that leaks gas into the cylinders after turning it off.

A fuel pressure test would help verify this.
Reply With Quote
  #13  
Old October 14th, 2017, 14:28
xjalfh xjalfh is offline
NAXJA Member
 
Join Date: Mar 2011
Location: NE
Posts: 6
Re: Momentary rough running about 1 minute after a warm start.

Well, I finally found a little time to dig into it deeper. It set a P0135 code (I'm sure that's the one it set last winter.) so I started with the upstream O2 heater circuit.

Rechecked the fuse for the heaters and it was good, with 14V on both sides when running.

14V at the O2 sensor connector on the feed side, but 14V on what should be the ground side as well. No voltage drop across the heater. So, it seems there's a bad ground.

Indeed, ohmmeter verifies open circuit on the ground side of the connector.

Looking at the wiring diagram, it goes to S107 then to G101. The ground tests good and was clean, but I cleaned it anyway.

I am still digging for S107 though. It seems that nearly everything grounds through the S107 splice, so I would think it would have to be quite the bundle of grounds. The manual shows that it should be inside the harness at the rear of the engine on pass. side. Still trying to find it.

Does anyone know where the grounding splice S107 is located?
Reply With Quote
  #14  
Old October 14th, 2017, 17:41
xjalfh xjalfh is offline
NAXJA Member
 
Join Date: Mar 2011
Location: NE
Posts: 6
Re: Momentary rough running about 1 minute after a warm start.

Gave up on looking for the splice that was supposed to be in its ground circuit, and backtracked from the connector on the O2 sensor. Should have started there in the first place instead of trying to work from the ground, backwards.

There was no apparent damage on the outside of the loom cover, but inside I found the wires had been pinched at some time and the ground wire completely fell apart when I took it out of the loom.

Don't know if it was just barely hanging on by a thread that it didn't always set a P0135 code (doubtful), or the heater hasn't worked for ages but conditions were just not right for setting a code until now when the lower temps start returning.

Now to redo the wire looms and tape I unnecessarily removed and hope it runs like a champ again.
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
1992 no start/occasional start rough running 831_xj OEM Tech Discussion 5 September 12th, 2015 10:05
Cold start fine, warm startup rough idle Forceful Llama OEM Tech Discussion 3 February 13th, 2015 22:38
Rough idle after warm start, Winter only Ghostrider OEM Tech Discussion 1 January 15th, 2014 21:41
Rough Start in semi warm tempratures oldmantompkins OEM Tech Discussion 3 February 9th, 2011 04:17
90 xj running rough when warm poomero OEM Tech Discussion 6 May 10th, 2009 22:22


All times are GMT -7. The time now is 09:41.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014