coffeehouse

So my 2000 cherokee sport 4.0L has developed this very strange misfire and i cant seem to figure it out. this misfire causes the jeep to buck hard at idle and under load,has no power, and it has a 3000 rpm rev limiter. it started out as a fouled plug smashed by carbon so i replaced the plug and the jeep had ran normal. for about a week atleast. then the misfire came back. yesterday morning i pulled the plugs none were broken all had a good gap. so after re installing them the jeep again ran fine all day long driving all over town. at night i took a ride up to a friends and as soon as i come off the highway the misfire comes back, cooled down drove home no problems again until i got off the highway. This morning i decided to test it and took the highway up a few towns got off and it misfired. I unplugged the batt to let the computer reset and took it the long way home (i.e back roads). computer did set a code and the check engine would flash but i did not get any bucking or loss of power. can someone please tell me what the hell is going on here??? I originally was guessing heat soak but it is ONLY after a highway drive.

Cummins93

You should have a stored code, read it and post the Diagnostic Trouble Code(s)

tjwalker

Agreed. The strategy for a vehicle that has had a check engine light and is symptomatic is always the same. Retrieve the code. Anything less is guesswork. For your vintage, that must be done with a code reader or a scan tool.

Post the EXACT code here for comment. Not just a description. With OBD codes, the devil is in the details.

And also know that a flashing check engine light indicates a serious misfire, which if not resolved quickly, will trash your catalytic converter. Don't drive this vehicle until you get it fixed.

wildcat08

actually on this rig you can turn the key from off to on 3 times and watch your digital display. it will display your trouble codes. no scanner needed just a reference for the pcodes

tjwalker

That trick won't work on a 2000 "Cherokee" regular XJ. That luxury went away mid-1997.

extrashaky

I'm assuming you don't have a code reader. As long as you're not in CA or HI, you can stop by Auto Zone, Advance Auto, O'Reilly, etc. and get your codes read for free. Just go in, tell them you have a check engine light and ask them to pull the codes. Sometimes they'll give you a printout with the code number and description. If they don't, WRITE DOWN the EXACT codes and post them here. The codes will each consist of a letter followed by four numbers, like "P0300." You will likely have multiple codes, so be sure to give us all of them.

If you're going to drive a 17 or 18 year old vehicle, you need to get your own code reader. You can buy a standalone scan tool, or you can use your smartphone with an OBDII adapter.

If you have an Android phone, you'll use the Torque app, which is free for the "lite" version and $6 for the full version (it's worth it). You'll need an OBDII bluetooth adapter you can order from Amazon for $15 to $30.

If you have an Iphone, you'll use the DashCommand app instead. You'll need an OBDII wifi adapter to work with the Iphone.

DO NOT use any software you get with one of those adapters. The adapters themselves work fine, but the software that comes on the CDs with them are often full of viruses. Use the apps noted above with your smartphone instead.

coffeehouse

Everyone relax. i thought i had the codes posted at the beginning of the thread. i do own my own scanner and the jeep has been scanned and shows p0301 and p0455. Cyl 1 has a brandnew high flow injector to rule that out for anyone.

Cummins93

What is the numbers on this injector?

Did you ever swap the original cylinder 1 injector to a different cylinder?

I chased a similar issue on my 95 and it turned out to be my injector connector. It wouldn't misfire until up to temp.

coffeehouse

i have not started swapping injectors yet. It will have a slight misfire when cold but its almost as if once the computer stores the code and it comes back to idle the engine goes into limp mode ( no power, horrible misfire, 3000rpm rev limit). once the code stores itself i can keep going on the highway and not have a problem. its as soon as i bring the engine back to idle or let it back down going down hill that it kicks in like this and once it starts its there until you get home,shut it off and restart it. then it will run normal for about 5 minutes or until you idle back down.

extrashaky

Several things come to mind. I'd start with the simple/free stuff first.

Have you tested compression? How was the compression on #1?

Swap the injector with #2 and see if the misfire moves.

Check the injector connector on #1 with a noid light. You can borrow one from Auto Zone if you don't have one.

Steam clean the combustion chamber. (link) You can also use Mopar Combustion Chamber Cleaner for the same purpose if you'd prefer to use a product.

There is a TSB that covers your year for a valve issue where the intake valves don't rotate properly at higher RPM, which allows carbon to build up and prevent the valves from sealing properly. (link) This procedure also involves cleaning the combustion chambers with the Mopar cleaner, then manually rotating the valves.

Pull the valve cover off and inspect the springs on #1 for damage. Any chance you or a prior owner swapped in a 0630 head for your 0331? There was a TSB for '96 to '99 for weak valve springs that would result in misfires.

Reindex the camshaft position sensor. (link) Seems like this issue usually affects #1 or #6, so it might be worth a shot. It's not difficult but can take a little time if you're working by yourself.

I'm probably missing something really easy that will turn out to be the solution.

coffeehouse

Turned out to be the lock for the electrical connector on the injector. it would rattle out as i drove and cause a misfire. Thanks guys!!!!

extrashaky

Basslicks

It's those little things that will just drive you nuts! Glad you got it figured out, man.

coffeehouse

It sure was. Especially being the only driveable car with my subaru sitting with a bad HG. Thanks alot guys !!!

extrashaky

Just curious...

There's a code for injector circuit failure. I can't recall the exact number, but mine throws it if I test circuits with a noid light. Did you ever get an injector code? Seems like this is the exact situation that code was meant for.