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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1525
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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2000 Cherokee missing runs at it s worse when trottleing

Customer Question

2000 Cherokee missing runs at it s worse when trottleing down from hi wy speed
Submitted: 1 year ago.
Category: Jeep
Expert:  Dan replied 1 year ago.

Hello, my name is***** the check engine light on? Does it idle good? Thanks.

Customer: replied 1 year ago.
check engine light on ,very slight miss at idle
Expert:  Dan replied 1 year ago.

Does the check engine light flash? Do you know what codes your getting? Thanks.

Customer: replied 1 year ago.
IT ONLY BLINKS WHEN ITS ACTING UP CODE 306 WHEN IT BLINK IT BEARLY MAKE IT HOME
Expert:  Dan replied 1 year ago.

P0306 is cylinder 6 misfire so this would be a problem that effects specific cylinder, most likely injector. Swap injector with another cylinder to see if misfire follows injector, if so replace. Here are replacement instructions, let me know how it goes or if you run into more questions. Thanks.

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https://www.dropbox.com/s/j23rg3wvpjbgd6v/injrr.pdf?dl=0

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Customer: replied 1 year ago.
OK I WILL SWAP INJECTORS AN SEE IF CODE CHANGES
Expert:  Dan replied 1 year ago.

Sounds good, keep me updated. Thanks.

Customer: replied 1 year ago.
ok dan move injector an still get codes put 6 in 1 an still get 306 plus 303 an 300 what now
Expert:  Dan replied 1 year ago.

Use a spark tester to test spark strength on each coil lead. They should all jump a 25kv gap. Let me know, thanks.

Customer: replied 1 year ago.
ok I will check it tomorrow thanks
Expert:  Dan replied 1 year ago.

Sounds good, let me know. Thanks.

Customer: replied 1 year ago.
not getting spark out of number 6 an number 4 ,an got po136 just came up.when I disconneded battery to charge it
Expert:  Dan replied 1 year ago.

Replace the ignition coil assembly. Let me know how it goes, thanks.

Customer: replied 1 year ago.
ok I ordered the coil pack soon as I put it in I will rate you thanks
Expert:  Dan replied 1 year ago.

Sounds good, thanks.

Customer: replied 1 year ago.
OK GOT THE COIL PACK ,DID NOT WORK SAME PROBLEM
Customer: replied 1 year ago.
WHAT DO YOU THINK ABOUT THE CHEROKEE
Expert:  Dan replied 1 year ago.

Still not getting spark out of 6 or 4?

Customer: replied 1 year ago.
RUNS GOOD AS SOON AS YOU SLOW DOWN WHEN COMEING OFF AN EXIT CHECK ENGINE LIGHT COMES ON AN STARTS BLINKING AN STARTS RUNNING BAD
Customer: replied 1 year ago.
WITH CODE 306
Expert:  Dan replied 1 year ago.

Check to see if cylinder 6 has good spark, if so next step is a compression test. Let me know, thanks.

Customer: replied 1 year ago.
ok te compression readings are between 135 an 145 ,there is spark at number 6
Expert:  Dan replied 1 year ago.

I'm not sure what to think of this one considering you keep getting a cylinder 6 misfire with everything checking out. I'll open question back up to see if someone else has some ideas.

Expert:  Juan Crespo replied 1 year ago.

Hi there.

I don't know if this would help you, but I've seen O2 sensor wires cause similar problems, and noticing you mentioned code P0136 popping up, I think you should check the wiring from the downstream sensor all the way up to the engine harness - pay close atention at the point where the harness breaks out to the injectors.

Please let me know if that helps.

Best Regards.

Customer: replied 1 year ago.
ok juan I will check the wires from the o2 sensor to the harness ,hopefully tomorrow if it does not snow thank ,I will get back to you as soon as I do that
Expert:  Juan Crespo replied 1 year ago.

Oh. boy... I hate that cold stuff ;-( - that's why I retired to the Caribbean :-)

Take your time and let me know what you find.

Best Regards.

Customer: replied 1 year ago.
OK ALL THE WIRES LOOK GOOD CHECKED EVERYTHING THERE
Expert:  Juan Crespo replied 1 year ago.

Oh, well... it was worth trying - I just doesn't explain why that P0136 popped up.

Anyways, back to the misfire on cylinder 6; if we have spark and fuel and static compression is within specs, the only other thing that could cause a misfire would be valves not opening and closing as they're supposed to - I've seen sludged-up engines where a lifter fails on deceleration and the valve doesn't open properly, or holds it open so the spring can't close it.

So, we are at the point where I recommend a good engine oil flush before taking anything apart. What do you say?

Customer: replied 1 year ago.
OK I WILL TRYT AN OIL FLUSH
Expert:  Juan Crespo replied 1 year ago.

OK. Make sure there are no signs of heavy sludge before doing the flush. If there are such signs, it might be too late to save that engine.

Customer: replied 1 year ago.
ok flushed engine still getting multiply misfires an as soon as I come off a highway run an decelerate in starts breaking down ,an I have to crawl back home an get the code off to make it work good again.it rides good when I drive in town but but as soon as I get on highway an decelerate it breaks down an startas running bad.i have to take the code off to make it run good
Expert:  Juan Crespo replied 1 year ago.

Thank you for that last bit of information. It all now starts to make sense along with that P0136 that popped up once. Go under the vehicle and start tracing the O2 sensors wiring all the way to the PCM. Check for any traces of burning by contact with the exhaust pipes or any thing that may have caused a short. If the wiring is good, then check the connectors at the PCM. If those are good, then the problem is in the PCM itself.

The reason I'm suspecting the PCM to be the cause of the issue is because of what you said about having to take the code off to make it run good. If the problem was actually caused by a misfire, erasing the code wouldn't have any effect on how the engine ran.

Best Regards.