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  #1  
Old September 4th, 2019, 12:46
coxj99 coxj99 is offline
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4.0 Loosing power, dying

1. 1999 XJ
2. 4.0
3. Auto
4. Differential/transfer case.

First time post, go easy on me. ;-)

Got an XJ a couple months ago because my buddy had one in high school - so I always wanted one - and I need a rig to take my kids out and go hiking, camping, hunting, etc.

I have done a few things:
- New fuel pump (Delphi)
- Fan shroud and 3 10" fans
- Added Transmission cooler
- Replaced the camshaft sensor
- Replaced the crankshaft position sensor

I have taken it on a few trips to the mountains in CO for camping. The first one I discovered the 2 9" fans the previous owner had installed don't cut it in 4 low. So I added the shroud with 3 10" fans and the transmission cooler. No problems there now!

On the way back from that trip and few short trips, I noticed some surging/tripping/stumbling when on the freeway. It was hot, so I didn't think much of it. Also had some hard times starting the vehicle warm. Between it all, I thought it could be the fuel pump, so I replaced it. I was happy I did because it seemed like I got 20 years worth of fuel debris out of there! (Nothing too crazy.)

I also noticed going up hills the cabin vent fans (no AC on this rig yet) some times would halt. Maybe it wasn't the fan, maybe it was a vent behind them would close. This reminded me of my dad's 1950 pickup that had the wipers run off vacuum lines and would pause when the truck was working hard....

Then I replaced the crankshaft position sensor, because I heard that was probably the source of the hard starts (cranking it a couple times to get it to sometimes start when the engine was hot). That seemed to have fix that.

PROBLEM:
But on the last couple trips, around town or from mountains (on 85-90 degree days), the tachometer has been surging 500-750 RPMs when cruising on the freeway or at stoplights. It has totally died twice (both times in parking locations). Before it dies it seems like it looses it's power and sounds like it is "choking."

Currently, it only has a cat - no muffler or tail pipe. Both oxygen sensors are in place. There is no check engine light. Clean oil (less than 1500 miles).

QUESTION:
Why does it keep wanting to die? What could be causing the RPMs to surge? What should I look at next?

THOUGHTS:
- Check for vacuum leaks
- Replace MAP sensor
- Replace throttle position sensor
- Check spark plugs (pulled one, normal wear)
- Plug cables seem fine
- Should I use Seafoam Spray? (since I don't know the full history of the vehicle)

PREVIOUS IDEAS:
- O2 sensors throwing off fuel mixture. Heard this would probably throw a code. But not having any tail pipe still has a bit of a question in my head.

I am sure I am forgetting something.... Feel free to ask and I would really appreciate any suggestions. I don't mind replacing things but I'd like to know - not shotgun guesses.

What should I try next? Thanks!
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  #2  
Old September 4th, 2019, 13:13
RCP Phx RCP Phx is offline
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Re: 4.0 Loosing power, dying

First thing I would do is to put a scanner on it. Just because there are no codes doesn't mean it's operating properly.
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  #3  
Old September 4th, 2019, 15:20
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Tim_MN Tim_MN is offline
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Re: 4.0 Loosing power, dying

Check for trouble codes. Use a code scanner that shows live data.

Make sure all the tune-up parts are fresh and good quality parts. Use plain Champion or NGK spark plugs.

Test the coil. Test the Throttle Position Sensor. Clean the Idle Air Controller and throttle body.

Only install genuine Jeep sensors. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.
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Quote:
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Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....

Last edited by Tim_MN; September 4th, 2019 at 15:24.
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  #4  
Old September 4th, 2019, 22:44
coxj99 coxj99 is offline
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Re: 4.0 Loosing power, dying

Took me a minute to find my scanner. And I don't know why I din't think of this... Thanks for the suggestion! I got:
- P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
- P0171 System Too Lean (Bank 1)

Well looks like it might be O2 after all.... Should I jump straight to sensor replacement or look at other possible causes? What else should I know?

I see that there could be an intake leak causing this. Would that just be in the intake manifold or throttle body?

Sidenote: I am planning on replacing the exhaust pipe (dented), and adding a tail pipe w/muffler, and might as well clean get a new catalytic converter, since I am doing the rest of that...

Today I cleaned the Idle Air Controller and throttle body (prior to reading, but glad I was thinking right). Probably could clean the IAC a bit more. Mine only had a seal on the controller. Several people on youtube mentioned an o-ring. I'll look at replacing that. Sounds like that could fix the rough idle or bucking while driving. Right?

No coil on this - has a distributor. I checked it and the cables, as well.

Thanks for the plug recommendation.

Questions:
- So buy sensors straight from the jeep dealer? Or is there a better place to get them?
- Should I just buy an assortment of o-rings? Seems like those are always good to replace if in question or missing, if you can find the right size. Finding the right size seems like a pain.
- Tim - What scanner do you prefer? I just have a basic OBD2 reader.

Thanks RCP Phx and Tim_MN!
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  #5  
Old September 5th, 2019, 00:23
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techno1154 techno1154 is offline
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Re: 4.0 Loosing power, dying

I was just about to post something similar. On a trip from West Tennessee to Florida, my XJ shut down when I stop at a light or slow to under 20 MPH. No problem at highway speed up hill or down hill. Some of the things mentioned here are what I plan to look at. I get no code on my Scan Gauge and no check engine light.
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1996 XJ; 4.0L; AW4; NP231; SYE; D30 and D44; ECTED; 4.10 gears; 30X9.5 -15 BFG/AT/KO; 3" lift; Rusty's LCA; JKS ADJ UCA; Kevins ADJ Track bar; Drawtite Front Receiver; Dual Electric Fans; Dual Battaries.
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  #6  
Old September 5th, 2019, 03:01
RCP Phx RCP Phx is offline
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Re: 4.0 Loosing power, dying

Quote:
Originally Posted by coxj99 View Post
No coil on this - has a distributor. I checked it and the cables, as well.
What scanner do you prefer? I just have a basic OBD2 reader.
I'm not sure what you meant by "no coil"?
I have had my Innova scanner for about 20yrs but it doesn't make any difference as long as you can read "live data".
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  #7  
Old September 5th, 2019, 04:59
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Tim_MN Tim_MN is offline
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Re: 4.0 Loosing power, dying

Test the O2 sensor function. Test the coil.

O2 sensors have a service life of about 75 - 125,000 miles and are routine maintenance. Install NGK/NTK O2 sensors only.

Most 4.0L Cherokees have or will develop an exhaust manifold leak, intake manifold leaks are not very common.



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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 .....
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  #8  
Old September 5th, 2019, 08:43
CJR CJR is offline
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Re: 4.0 Loosing power, dying

coxj99,

Good suggestions have been offered. Here's what I suggest checking;

1. Since you installed a new fuel pump, it's possible that the 500-750RPM surging could be caused by injectors not closing completely and leaking excess fuel into engine. Do a good injector cleaning to see if it helps.
2. Likewise, the injectors have a firing order and the injector wires are color-coded. Check to make sure the proper colored injector wire is connected to the proper injector.
3. Sometimes if the wrong sized o-ring is used in the idle control valve (ICV), the o-ring can be crushed and allow additional air to enter the ICV. As a check, pull the o-ring and seal with RTV and check for improved idle.
3. I bought a used 88XJ that had an manifold air leak that was hard to find. The PO had cleverly used aluminium epoxy to patch the aluminium manifold crack. In time, the aluminium epoxy developed a hairline crack which allowed excess air to enter the engine.

Hope this helps.

Best regards,

CJR
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  #9  
Old September 5th, 2019, 09:14
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old_man old_man is offline
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Re: 4.0 Loosing power, dying

For good measure, before diving in, run a can of BG44K through the gas. It will remove carbon and clean the injectors (a common problem on older engines). After that, pull all the plugs and do a reading. Stay away from the new design plugs. The old Champion's seem to work the best.
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  #10  
Old September 5th, 2019, 15:15
coxj99 coxj99 is offline
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Re: 4.0 Loosing power, dying

Thanks all for the suggestions. I certainly have plenty to test and do. I'll post back after I make some progress!

RCP Phx - Sorry I was confusing the 2000/2001 coil-on-plug ignition system. Duh. Feel like an idiot. Thanks for setting me straight!
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  #11  
Old September 18th, 2019, 12:00
coxj99 coxj99 is offline
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Re: 4.0 Loosing power, dying

Progress update...

I replaced everything between the exhaust pipe through the tail pipe. New NTK Oxygen sensors. Thanks for the recommendation. That fixed the P0138 and P0171 codes it seems. I am happy with the exhaust.

I have put a bottle of Red Line SI-1 Fuel System Cleaner in. I use Red Line with my motorcycles and trust them. I don't think I have driven it enough to make much of a difference. I put it in a mostly full tank and haven't used much gas yet since getting all the last minute exhaust hangers in and having to cut, straighten and weld the tail pipe took had me not driving it.

It also appears that my P1391 code is back. I have replaced the CMP with a sensor from a spare distributor I had, and last night also tried a NAPA Echlin one. Problem is still there. Replaced the CKP sensor with one I bought a few months ago at Autozone (sorry), and the code is still there. I have a NAPA Echolin CKP sensor, that I will try as well. But I am doubtful, that is the problem. I have the factory maintenance manual, so next I was going to probe the connections for continuity, wiggle them around, and check to make sure they go to the right places. I can generally get it to start after 2 cranks, but have issues with starting after the vehicle is warm.
2 questions here:
1) Could the CKP/CMP fault have anything to do with my surging?
2) Any suggestions or need any other information?

I also got NAPA Echlin Throttle Position Sensor. Changing that appears to have changed nothing. Thinking that isn't the problem.

- I haven't tested the coil.
- Distributor, wires, and plugs look fine but I don't know when they were replaced prior to my ownership. I did swap the CMP sensor, but no change.
- I did put the o-ring back in on the ICV and added some RTV for good measure.
- I have cleaned the throttle body.

I think testing the coil is next. And driving it everyday around the house so I don't get stuck, to work the fuel system cleaner through the tank.

2 things I noticed when running the XJ now:
1) When starting I have to feather the gas to keep it from dying. Is that a factor of the computer needed to adapt to the new exhaust system? Or do I need to get it tuned?
2) When driving at 50-60 on a flat highway, I still notice the RPMs bouncing 500-1000, but I also noticed I could feel it start to surge, just before I saw the gauge spike. I didn't remember that before but doesn't mean anything changed.

I also got a P0705 when I stopped to top off the tank (hopefully mix the cleaner in). I have an NSS switch from our Jeep used parts supplier, that I cleaned up when I got a code (can't remember which one) but then didn't put it in because the code stopped showing up. Think I will replace with used part, and if that doesn't do it, then get a NAPA replacement. I occasionally have to bump the shift lever to allow the key to be removed. Sidenote, I am planning on draining the transmission pan, and replacing the filter and transmission oil pan gasket. Replacing the fluid with Castrol Dex/Merc (not the high mileage stuff, and not the ATF fluid later recommended by Chrysler). Do you see harm in doing that in any order, or deal with the NSS switch first?

I don't see how the P0705 could have anything to do with the surging. Correct?

All help appreciated! Any other suggestions?
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  #12  
Old September 18th, 2019, 12:24
RCP Phx RCP Phx is offline
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Re: 4.0 Loosing power, dying

If the trans tcu can't figure out what gear your in then ,yes I would say you need to start with the NSS.
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  #13  
Old September 18th, 2019, 16:59
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Tim_MN Tim_MN is offline
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Re: 4.0 Loosing power, dying

Read this part twice >>> ONLY use genuine Jeep engine sensors. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Even NAPA sensors are not as good as they used to be.

Cheap parts are cheap for a reason.


A simple NSS test is bypass it temporarily.




Quote:
Originally Posted by coxj99 View Post
When starting I have to feather the gas to keep it from dying.
This symptom very strongly points to low voltage. Low voltage will cause hard starting, having to feather the gas to idle, and random stalling.


For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving and the engine will sometimes start and idle normally.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine maintenance for good starting.
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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 .....

Last edited by Tim_MN; September 19th, 2019 at 07:44.
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  #14  
Old September 18th, 2019, 23:49
coxj99 coxj99 is offline
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Re: 4.0 Loosing power, dying

Tim - Thanks! RCP - Thanks!

Good idea on bypassing the NSS. I looked that up. Will that make the code go away, then I can see if the problem still persists? I got down there to clean up the NSS area, and noticed that the tabs are not bent up around the nut.... I am am guessing that it is constantly changing/slipping. Hopefully, I just need to clean and recalibrate - from what I have read...

Thanks for mentioning low voltage. Ironically, the day before I left the ignition switch on over night after checking for codes..... I put it on the trickle charger, but it is not fully back up. I'll still get it tested under load. I want to replace all the battery cables but one thing at a time. Don't know why I didn't mention the discharged battery. Lame.

Noted on the sensors. Thought NAPA was above the cut. Some people were telling me Jeep just goes to the lowest bidder for their old OEM stuff, so I figured a reputable independent source might be a good option.

Thanks for telling me how the computer reboots. That is helpful.

Also thanks for recommending the IAC cleaning and the injector cleaner as routine maintenance.
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Old September 19th, 2019, 06:39
asymptonic asymptonic is offline
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Re: 4.0 Loosing power, dying

Quote:
Originally Posted by coxj99 View Post
Noted on the sensors. Thought NAPA was above the cut. Some people were telling me Jeep just goes to the lowest bidder for their old OEM stuff, so I figured a reputable independent source might be a good option.

No. I can relate that I learned my lesson on engine management components a couple of times. One was a "reputable" TPS that made the engine go nuts until I put the old one back in. Replaced w/ a Mopar that worked fine. If I can find them I use OEM for all sensors.
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