Check Engine Light (MIL) - Need your input

2001 Cherokee, 4.0L 4X4, Automatic.46K
Problem: Check engine light is on. Took to dealer since it had limited power train warranty. Lots of carbon based on their inspection and they chemically treated but still got the light so they rebuilt head, changed oil and put in new plugs. Light was off and car is "fixed". 10 days later, light came back on. Car back at dealer, now they say it's fuel pump and possible fuel pump module. Parts are on backorder and car is at dealership. Anyone had this problem? Suggestions?

Thanks in advance.

Dealers usually have not so great techs that just throw parts at your car until it works instead of diagnosing. But if its under warranty and you don't have to pay... throw away techs. As long as you have a 2nd vehicle while the jeep is in house.

What exactly is your problem though?

Rough idle and check engine light on. Dealer did a goodwill repair (N/C) and replaced fuel pump module. Will see if problem goes away.

2000-2001 JEEP CHEROKEE
ROUGH IDLE / MULTIPLE CYLINDER MISFIRE

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1801301 - ROUGH IDLE AT COLD TEMPERATURES
Date: 06/11/01
Model Year(s): 2000

Description: Some vehicle engines may exhibit a rough idle and / or Malfunction Indicator Lamp (MIL) light on condition upon initial start-up after a cold soak when temperatures are below 50 degrees F (10 degrees c). This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software (Cal level 00Cal15C).




1801001 - ROUGH IDLE AT COLD TEMPERATURES
Date: 04/20/01
Model year(s): 2001

Description: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L (ERH) ENGINE BUILT PRIOR TO APRIL 30, 2001 AND CALIBRATION LEVEL PRIOR TO (LESS OR LOWER THAN) THOSE LISTED IN THE OVERVIEW ABOVE. This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software (WJ/TJ ? calibration level 01Cal14C, XJ ? calibration level 15B.)

Details: Some vehicle engines may exhibit a rough idle and/or MIL light ?on? condition upon initial start-up after a cold soak when temperatures are below 50°F (10°C).




0900303 - 4.0L MULTIPLE CYLINDER MISFIRE
Date: 08/01/03
Model Year(s): 1999-2004

Description: NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L ENGINE. This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.

Details: The customer may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 50 - 70 MPH and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0 C (32 F).

If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Multiple Cylinder Misfire. Various single cylinder misfire DTC?s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in ?Limp-In? mode.

The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

This condition may occur when the engine is not allowed to run at engine RPM?s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM?s and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.




1803103 - 4.0L ROUGH ENGINE IDLE AFTER RESTART FOLLOWING A HOT SOAK
Date: 09/05/03 (supercedes 1802702 dated 09/06/02)
Model Year(s): 1999-2004

Description: NOTE: This bulletin applies to vehicles equipped with a 4.0L engine. This bulletin involves the installation of a fuel injector insulator sleeve.

Details: Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector #3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder #3 until the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3 temperature to a point below which the fuel will not normally vaporize.

If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.

Parts required:
56028371AA Ignition Wire Shield

Repair procedure:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length. See diagram.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o'clock position (from driver?s side of vehicle).

Thanks Ghetto2315 for the info. Yes dealer did a decarbonization but MIL still came on. Took it back and they replaced fuel pump module and so far no more MIL. Happy motoring!

Problem is back! MIL is on again. Been only two months since dealer serviced it. Engine idles and runs fine but light is on. I did noticed that there was quite a bit of pressure in gas tank when I opened gas cap to make sure it was on tight. A big whoosh when I opened cap. I suspect that problem is in fuel system, so I replaced with new gas cap. Still get the light but I drive it for a few days to see if light goes out. I'm tempted to disconnect battery to reset and see if it comes back. But there is finally an Autozone near me now so I may take it down there this weekend and have them read the codes. My Jeep was manufactured in 12/2000 and is a 2001 model. I want to look at everyone opinion and suggestion before going back to dealership and spend anymore money, it already costed me $300.00 for decarbonization last time.

Thanks in advance.

Well... that "whoosh" when you open the gas cap is normal so I suspect that it has nothing to do with the pressure. It very well might be your fuel pump, as it was with mine, that may be causing the problem.

I suggest taking it back to Autozone to have them scan for the codes for free and then see what code is lit.

Are you sure its not a cylinder misfire?

Ghetto2315

Dealer previously said "fuel pump module failure". They replaced module PN 14500103 bad pump sensor PN 5012953AC. Is there a TSB on this?

Will take car to Autozone this weekend for code reading. Will post code(s). Thanks again for responding.

OK, I went to Autozone to "rent" the code reader. I got four codes, P0135, Bank 1-Sensor 1, Oxygen Sensor Heater Circuit Malfunction; P0158, Bank 2-Sensor 2, Oxygen Circuit High Voltage; P0141 Bank 1-Sensor 1 Oxygen Heater Circuit malfuction; P0161 Bank 2-sensor 2 Oxygen Circuit. So...what should I be looking for to replace, Oxygen Sensor? Where and how many?

Obviously your XJ is unhappy with the oxygen sensors. There will be one on each exhaust manifold. Should be the only sensors on the manifolds. They could be bad, but if both are throwing the same codes there may be something else going on like a bad ground. But more likely an overly rich condition caused them both to go bad. Replacing both may solve the problem, but if there is another condition that caused them to go bad, the replacemnts won't last long.

The 2 banks means it has a front and rear 02 sensor. The 1st bank is the headerpipe #one... if they are both that shot, good chance your cat might not be far behind too

I agree, the O2 sensor is very unhappy but the question is which of the four? I looked at shop manual and saw diagram and it show 4 sensors, 2 upstream (before cat) and 2 downstream (after cat). Diagrams show forward(front of car) manifold/cat as 1; rear manifold/cat as 2. 1/1 is the upstream forward sensor; 1/2 as downstream forward sensor; 2/1 as rear upstream and 2/2 as rear downstream. So the big question is the code P0135, bank 1 sensor 1 referring to the front upstream sensor and code P0158 bank 2 sensor 2 is the rear downstream sensor? I want to make sure since the sensors are $131.00 for the upstream and $69.00 for downstream. I could need 3 sensors since I have 1/1, 1/2 and 2/2 so I want to be sure. Thanks a million.