99 XJ engine randomly dies, how to troubleshoot?

[tdicola]

Hi all, over the past couple weeks I've noticed some problems with my '99 XJ that seem to be getting worse. Here are the symptoms:

- Randomly one or twice a drive the engine will stumble or completely cut out while waiting at a stop light. Foot is on the brake and transmission (automatic) is in drive. If it stumbles I'll briefly see the RPM drop to almost zero, feel the car shake a bit, and then instantly the RPMs will jump back up to about 6-700. If it dies, the engine will cut out and I have to put it in park to restart it--it always fires right back up.

- Twice now (in just the past 2 days) the engine has cut out while driving. Once on the freeway and once going through an intersection. I'll be driving when suddenly pressing the accelerator doesn't do anything and the car starts coasting. On the freeway the engine somehow restarted itself after a few seconds. Going through an intersection I had to stop, put it in park, and fire it back up (yeah, that was not fun).

- When these problems occur they rarely turn on the check engine light. If the light does come on, as soon as I start the car back up the light is gone. I tried pulling codes but nothing is stored.

- Twice while driving on the freeway I've had random jolts while driving. It's the weirdest thing, I'll be driving at freeway speeds when the car and drivetrain will shake almost like the transmission kicked into a low gear (RPMS don't go screaming up though).

Here are a few more details about my car too:
- 1999 Jeep Cherokee
- ~175k miles
- Automatic transmission, 4 wheel drive

Anyone have ideas? I'm really scratching my head as to what the problem could be. Searching around for my symptoms show just about anything could be at fault--fuel system, throttle body, sensors, torque converter, etc. Anyone have hints on how to start troubleshooting, or experience similar problems? It's getting to the point that I really can't trust to drive the car daily. Random engine stalls while stopped are annoying, but the engine cutting out at speed is dangerous.

 

[995speed]

I had a similar issue with my 99 XJ its got a 4.0 with a manual it actually turned out to be my front 02 sensor. I had similar issues it wouldnt die completely on me but the rpms would drop really,really low much lower than the 700 or so rpms and i would notice that the trucks motor would surge at highway speeds. I deff would replace that front 02 sensor cause thats what it was for me.

 

[Tim_MN]

Start your testing and inspecting. Look for damaged, loose or corroded wire plugs. Look for chafed or melted wire insulation, and pinched or damaged wires.

Clean and snug all your ground wires. Test your battery.

Most likely you have a failing engine sensor, and the Crankshaft Position Sensor and the O2 sensors are the most likely cause of your symptoms. They should be tested. Engine Sensors are routine maintenance items that have a definite service lifespan and should be replaced when they test out of specification or fail

 

[birchlakeXJ]

Classic symptoms of a failing crankshaft position sensor.

 

[sidewaysstarion]

I had almost the same issue on my 99 and replacing the O2 sensors fixed it.

 

[muduck18]

Classic symptoms of a failing crankshaft position sensor.

Ditto

 

[JohnX]

As said, o2 or CPS are likely. Don't overlook the simple things like state of tune, plugs, wires, cap, rotor, etc. You can have a minor issue that causes and out of tune engine to stall.

 

[muduck18]

I had almost the same issue on my 99 and replacing the O2 sensors fixed it.

The o2 sensors will throw an engine liight 99.9% of the time.

The Crank position sensor will not.

It will get worse and worse until the Jeep won't start any more, or it takes a really long time to start and back fires occasionally. then won't idle.

(at least those were my symptoms for the CKP on my rigs)

 

[tdicola]

Thanks for the advice. As far as I know the CPS has never been changed so it wouldn't surprise me if its going bad. Is there any way to test the sensor with a multimeter before replacing it?

 

[muduck18]

yes, there is, but I don't know it off the top of my head, Search around a little, its here somewhere.

 

[hubs97xj]

http://www.naxja.org/forum/showpost.php?p=245575461&postcount=3

^Test procedure Tim has posted many times.

And this may also be relevant.

The CPS diagnostic above is fairly specific and has several checks and tests, some slightly technical, and some dead simple, that will either include or exclude the CPS as the root cause of the no-start. If the no-start isn't a CPS fault, you will know right away.

Testing the fuel pump can be as simple as listening for it to run when the key is turned to ON. Testing the fuel pressure is also simple.

 

[sidewaysstarion]

The o2 sensors will throw an engine liight 99.9% of the time.

The Crank position sensor will not.

It will get worse and worse until the Jeep won't start any more, or it takes a really long time to start and back fires occasionally. then won't idle.

(at least those were my symptoms for the CKP on my rigs)

Not true, My O2s were toast at 160K and I had no CEL's, swapping them out fixed my random stalling and chugging.

 

[Boss Cherokee]

I had sporatic no-start and stalling about 3 years ago on my 95 auto 4.0 4x4. The code read CPS PO340 so I replaced the CPS and it fixed the problem.
Fast forward to today
My 1999 is starting but with occasional difficulty. It surges and drops RPM's as if to stall but regains. It runs but will still surge on occasion. I will test CPS as Tim suggested, which by the way is a great explanation and write up Tim Thanks from all of us if you haven't heard it!
My dilemma will be if I can't make heads or tails of it can I try my 1995 CPS sensor on the 1999 for a test drive of the O2 sensors to eliminate the O2 sensors as a possibility? Since the O2's have been posted in this post as a potential cause for the surges, I don't want to replace them unless I have to! I have not checked to see if the CPS's are the same part #'s and I will shortly, but sometimes parts manufacturers just change the part #'s to confuse the general public, kinda like politicians and propositions!!

 

[sidewaysstarion]

The front O2 sensor is $20 bucks, If it's old I'd replace it anyways, you're fuel mileage will probably improve as well.

 

[Ecomike]

I would have put the TPS at the top of that list as well?

Start your testing and inspecting. Look for damaged, loose or corroded wire plugs. Look for chafed or melted wire insulation, and pinched or damaged wires.

Clean and snug all your ground wires. Test your battery.

Most likely you have a failing engine sensor, and the Crankshaft Position Sensor and the O2 sensors are the most likely cause of your symptoms. They should be tested. Engine Sensors are routine maintenance items that have a definite service lifespan and should be replaced when they test out of specification or fail

 

[Boss Cherokee]

The front O2 sensor is $20 bucks, If it's old I'd replace it anyways, you're fuel mileage will probably improve as well.

Sure their $20.00 My wifes Rover are $80.00 and there's 4 sensors. dual exhaust at header pipe and post cat and she needs 3 of them! SUCKS!

 

[Boss Cherokee]

Can anybody answer if CPS sensor for a 95 will interchange with a 99??

 

[birchlakeXJ]

Can anybody answer if CPS sensor for a 95 will interchange with a 99??

Google a parts site like RockAuto and check it out. I doubt it will interchange.

I buy my crank sensors ONLY from Jeep. Money is about the same. Crank sensors are "hit and miss" with a lot of miss.

 

[Tim_MN]

The TPS, CPS, and O2 sensors can be tested. O2 sensor have a service life of about 125-175,000 miles. The CPS commonly fails in the same mileage range. If you need a new one, you need new one.

I would have put the TPS at the top of that list as well?

Considering the symptoms described, the TPS would be farther down on the list for me.

The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. A TPS may fail gradually ( unless submerged in water or sprayed with pressurized water ) leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

 

[Boss Cherokee]

Thanks guys I some what fix the problem of the rough idle. The O2 sensor connector was the culprit. When I changed out the tranny 6 months ago, one of the four pins reseeded into the plastic housing causing intermitten contact until all contact was lost. I fixed that and it runs like a champ, BUT I can't get the check engine light to stay off. I erased the DTC's and it came back on. I disconnected the battery for 1/2 hour it came back on and is showing the PO340 sensor A circuit bank 1 code but when I switch the decoder to Chrysler it gave me a P1391, a loss of CMP CKP which I believe is the same as the first code. I will replace O2 because I think it could be fouled from running like that for over 6 months and then if needed the CPS. It does have 191K but I don't know if the've been replaced (my son was second owner, we bought it off him because he was going to be gone for 4 years USCG)? Hard to believe since it runs so well!