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01 XJ 4.0 starts stumbles then dies

BIGDOGGP739

NAXJA Forum User
Location
Redmond Oregon
Hey all. I have a new to me 2001 XJ. It has a shop installed reman motor with around 5k miles on it. I have had it for a few months and this problem has been persistent since day one. Today I cannot get it to run. Here is what happens and what I have checked...

When I turn on the key, you can hear the fuel pump prime for a few seconds.

Turn the key to start and it will crank, fire and run for 1-3 seconds then dies HARD.

Up till today I was able to do this several times and hold the throttle down to get it to finally run. When it did finally run, it was rough, exhaust smelled like bad fuel, and would not idle on it's own.

Checked fuel pressure at the rail and it is around 47psi and holds steady with no evident leak down.

Sprayed starting fluid in throttle body and it will run for 10 sec or so.

It is getting fuel, air, and spark. My thought is that it must be an electronic signal from a sensor?

The battery (6 month old yellow top) did get low a few weeks back, but it never died to the point of no start. I noticed that my voltage is around 13 v when running which seams a bit low. I also noticed that my lights were dimming with the stereo the day before it would not start. Maybe a dead cell in the Optima? Could this cause the stated issue?

This is my third XJ, and by far the newest and nicest. It has thousands of dollars invested and it just sits in my garage. I decided to give it some daily love last week, and now it has left me stranded.

I am mechanically inclined, but work 12 hour days without much time to do hours of troubleshooting.

At any rate, I need to get this baby back on the road. Please let me know if you have any insite to help a brother out.

Thanks in advance.
 
any check engine light? does the rpm gauge drop to 0 and come back up when its stumbling? if so its most likely the crank sensor.
 
No CEL. Did have one code for an EVAP leak that has been there all along, but it was inactive. The RPM do not fluctuate like a bad CPS. The CPS has also been replaced within the last 5k fyi.

Thanks.
 
The sympotms do not suggest the CPS at all. The symptoms do suggest low voltage.

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 at 13.8 to 14.4 volts, (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 PCM, the ground wires at the coil, and the ground wires at the oil dipstick tube. You must remove, wire brush, 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 preventative maintenance for smooth starts.
 
Tim,

Thank you for the well thought out response. I will check the charging/starting system and corresponding wiring this evening. I would venture to guess that my battery has gone bad from sitting for extended periods of time. I will let you all know what I find.

Thanks again!
 
Not withstanding anything that was previously said, as thinking things through is a good thing. But I have an '01 and the symptoms you mentioned are identical to a 'T'. I changed out the crank position sensor and all in the world was fine again. Not saying it is YOUR issue, but just throwing it out there. It cost under $20 and I changed it on my lunch break at work, really simple.
 
A faulty CPS typically results in a no-start with no spark at the plugs, or random unexplained stalling. The symptoms described point more to a PCM reboot than to a CPS problem. YMMV.
 
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I went through 2 cps before i got a good one from parts store.
and the one i have now im convinced its faulty as well
 
I went through 2 cps before i got a good one from parts store. and the one i have now im convinced its faulty as well


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 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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