2000 Cherokee 4.0 auto with 154xxx miles. Just started doin it this morning on my way to work. I didnt let it warm up at all and just took off and its fairly cold this morning, about 50*. Sitting in stop and go traffic, the Cel would be on but not flashing and the idle would be about normal. Basically whenever i step on the gas it starts flashing. Also i cant rev over 2800 rpms. I know i need to get the codes read tonight but i just wanted to post this now and see what peoples thoughts are. Thanks guys.

 

Limp mode, not good. I wouldn't drive it.

Get those codes asap!

Check to make sure the coil rail is seated and all hoses are good as a start.

 

What he said!!

 

my jeep done that few months back. it's a 2001. turn out to be coil pack. was the third coil pack i replaced.. lucky pep boys have life time warranty on them.

 

Anything less than reading codes is pure guesswork.....

 

Just drove it to get lunch and it ran fine. CEL is on but not flashing and it didnt idle rough at all.

Im getting it scanned on the way home from work.

 

So i got it scanned at Autozone. Code P0301 Cylinder 1 misfire.

On the way home from work the Cel was on but wasnt flashing and it ran fine. Not sure if this morning was because of cold temps or what?

 

My EXACT problem. Same year too.

Check your radiator for air bubbling up. Check it from a cool (not cold) start with radiator cap off before it gets hot.
Pull your spark plugs, and replace them. Check them again after 500 miles of driving.

I have also suspected bad coil packs and/or injectors.

If the CEL flashes, just turn the Jeep off, cycle the key five times or so and it will reset. I have even done a rolling reset (down hill of course).

 

cheapest things are the plugs, when were they replaced last, every 30,000 miles is the interval.....and the longer you run on a fouled or weak plug the more you increase the chance of damaging the ignition coil

 

I would approach a P0301 on a 2000 in this order...

1. Spark plugs. Absolutely positively must replace it, even if they are newer. Gotta rule it in or out early in the troubleshooting process. I recommend NGK plugs for the 00-01 and be sure they are gapped to .035

2. Coil rail connector TO the spark plug on that cylinder

3. Fuel injector (swap the injector from cylinder #1 to a different cylinder and see if the misfire follows to that cylinder)

4. Coil rail

5. Something internal to that cylinder. Run a compression test for starters.

 

There are multiple misfire issues on the 00-01 models and the causes can vary.

Heat soak misfire. After driving at full operating temp, stopping anf letting it sit for 10-15 minutes the heat from the exh manifold migrates into the injectors. Usually on the the 2 and 3 cylinders and will boil the fuel causing a vapor lock and throwing the CEL codes. Since yours was not operating at full temp and this one may not apply.

Bad coil pack. Simple fix and easy to replace.

Bad plugs. Again, simple and easy to replace.

Leaking manifold gaskets. The very back bolt for the intake/exhaust manifolds on the 00-01s likes to back out a little and cause a vacuum leak. The extra unmetered air can cause a false misfire CEL on different cylinders. Sometimes all it takes it to simply retorque that bolt back to factory specs and clear the codes, or possibly replace the gasket. This gets tricky to diagnose because the CEL can read one cyl at a time or multiple cyls at once. It can even read P0300, multi cylinder misfire and not designate which ones.

Disconnect the battery to clear the code to start with. The XJ takes a minimum of a 50 mile drive cycle for the computer to relearn the sensors and rediscover any codes. Mine would run like brand new after clearing the codes but at exactly 50 miles would fall on it's face and couldn't get out of it's own way from the stumbling. After fixing the gasket issue I have not had any other issues and gained 2 mpg back.

 

Looks like i got some work to do this weekend. Spark plugs were replaced about 5000 miles ago, theyre just Champions. Thats what ive always run in Cherokees with no issues before. Are NGKs actually better? If so how?

Ill try moving the injector around though thats a good idea.

 

Before moving the injector clear the code go a drive and see if it comes back. If the CEL does come back on the same cylinder then try swapping the injector, clear the code and drive it again.

 

Champions are fine for now. NGK are better, but they alone won't be why you have a flashing CEL 0301. The flashing "safe mode" (rev limited) CEL usually indicates more significant issue. Not always, but the trend is there.

 

Don't rule out a spark plug until you replace it. What if the insulator cracked? I've seen it happen. It takes 5 minutes to change a plug. I'm not saying that is the problem. I am saying that you need to rule it in or out. If you don't, you might be chasing your tail. I've not had much luck catching my tail.

Heat soak is usually on cylinder 3.