Question about 2002 Jeep Liberty

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2002 Liberty 3.7 Recent new heads, coil packs, plugs. At dealer compression OK , leak down test OK. was running perfectly then random misfires, spark advance jumping from 0-17 at idle.. At speed all is well. Its driving me nuts! Please help..

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  • Rich Kirby
    Rich Kirby Aug 01, 2013

    Running MAC Taskmaster which is how I know the swing of the spark advance. Heads are new and have been rechecked, no valve noise, no detonation, fuel pump at normal operating volts and pressure. This problem ONLY occurs during idle and start up, while driving all is fine, MPG is perfect, power is perfect, no check eng lights on.. This only occurs while at idle

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  • Jeep Master
  • 12,223 Answers

You must RUN the scanner/computer for better diagnostic. You can have fuel system malfunction, detonation, valve noise, valve adjustment is set too tight, , intake manifold system is leaking.Engine fuel pump is defective+pcm (ignition system).In short the electronic is complicated now in vehicles.
God bless you

Posted on Jul 31, 2013

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Posted on Jan 02, 2017

SOURCE: had a misfire mainly on

did you ever get this fixed? i have same problem with cyl 5 it's driving me crazy...

Posted on Nov 20, 2011

GARYca
  • 672 Answers

SOURCE: 03 Jeep Liberty random misfire

try checking your ignition coils and also the power wires to them!!Hopefully this helps....

Posted on Jul 15, 2009

BCAS1298
  • 3092 Answers

SOURCE: 2002 Jeep Liberty Sport 3.7L

We have an 02 Liberty 3.7L, here at my repair shop, after customer replaced, spark plug's and all coil pack's, brought it here to my shop, was running with two cylinder's miss, did cylinder compression test, no compression on two cylinder's, remove valve cover's, found two rocker arm's off, remove cylinder head's, and found that on those two cylinder's the valve seat's had drop, keeping the valve open, and that's why the two rocker arm's had come off, do a cylinder compression test, could be the same thing, hope this was very helpful.

Posted on Aug 30, 2010

ZJLimited
  • 17970 Answers

SOURCE: 2005 jeep liberty engine misfire cylinder 5

A code P0305 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer


If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Hope this helps; also keep in mind that your feedback is important and I'll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using Fixya, and have a nice day.

Posted on Dec 07, 2011

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I have a miss fire on cylinder 2and 3 I have changed coil pack ,spark plugs and wires still have the missing in it did not make a difference what else can I do


Is the computer code coming up as a misfire or are you actually feeling the misfire when you drive? Make sure all the grounds for the coil packs and engine are solid and clean. Many times there is rust corrosion under the pack or the retaining screws etc, Low compression can feel like a misfire as well. If all items are OK do a compression check to verify its not an issue.

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p0306?
misfire means, low combustion energy on #6
  1. bad spark,
  2. bad injection,
  3. bad compression
there are tests for each one.

i always check compression first. that why i dont spend a fortune
guessing. 30min.,labor , done wide open throttle, 150psi min.

i also heck the fuel pressure doing the SOP leak down test. (fSm)
then the injector balance test at same time.
finds leaking injector and clogged.
got cops?
you could have swapped coil packs COPs to see if that cured mifire.
swap any other with #6
if problem follows the coil pack COPS, then its bad.
my v6 had a 3 coil pack and cant swap just one coil. all 3 or none.

the misfire is real. you can feel it and the PCM measures it.

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2002 Jeep Liberty Sport 3.7L V6 Replaced all six spark plugs with brand new ones and replaced coils for 4 and 6 with new ones Still reading misfire Within 10 minutes of starting enging, vehicle idles...


We have an 02 Liberty 3.7L, here at my repair shop, after customer replaced, spark plug's and all coil pack's, brought it here to my shop, was running with two cylinder's miss, did cylinder compression test, no compression on two cylinder's, remove valve cover's, found two rocker arm's off, remove cylinder head's, and found that on those two cylinder's the valve seat's had drop, keeping the valve open, and that's why the two rocker arm's had come off, do a cylinder compression test, could be the same thing, hope this was very helpful.

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Hello
Here is what to check let me know if you need help checking this out
most common misfire causes on the cars I've worked on have been:
  1. Spark plugs
  2. Spark plug wires
  3. Ignition coil
  4. Fuel injector
  5. Wiring to fuel injector
  6. Timing Belt
  7. Vacuum leak or stuck open EGR
  8. Contaminated fuel or bad fuel pump
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I have a 2002 TrailBlazer with the straight 6,diognostic check said #3 cylinder was dead or misfiring, also map sensor showed up. #3 cylinder was misfiring, so to test the coil pack I swapped #3 coil pack...


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Hi there,

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As you have not indicated any codes from 301 - 306, then the computer has not been able to identify which cylinder misfired.

Therefore, you will need to begin checking for possibilities which could trigger the random (or multiple) misfire, which can be anything from:

- air leaks (this can disrupt readings on the engine's computer). Try spaying liquid around the inlet manifolds, check hoses etc for leaks.
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