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sprinkles08
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 22403
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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Alot mis fire at low idle, 172xxx 4.0, Jeep cherokee xj 01,

Customer Question

Alot mis fire at low idle
JA: How many miles are on the car? What size is the engine?
Customer: 172xxx 4.0
JA: What is the model/year of your Jeep?
Customer: Jeep cherokee xj 01
JA: Are you fixing your Cherokee yourself? What have you tried so far?
Customer: Crankshaft position sensor Tps new spark plugs
JA: Anything else you want the mechanic to know before I connect you?
Customer: I checked volts and continuity on all sensors every thing is in spec
Submitted: 7 months ago.
Category: Jeep
Expert:  david craig replied 7 months ago.

Hi Im David, what cylinders are misfiring?

Customer: replied 7 months ago.
1 and 6 and ive had other codes but i have yet to not see p0301 and p0306
Expert:  david craig replied 7 months ago.

Ok. do you have a noid light?

Customer: replied 7 months ago.
No i do not i did check injectors with multimeter and with thesascope checks out good
Customer: replied 7 months ago.
Can i check injector wiring with the multimeter ?
Expert:  david craig replied 7 months ago.

so you can hear the injectors clicking?

Customer: replied 7 months ago.
all clicked all sound the same
Expert:  david craig replied 7 months ago.

have you done a fuel pressure test?

Customer: replied 7 months ago.
i have 45psi at the rail
Expert:  david craig replied 7 months ago.

have you done a back pressure test?

Customer: replied 7 months ago.
I would only mis at a red light but if i turned it off and back on at the light the miss was gone i rebooted the pcu and now its worst i is sluggish and misfires all the time no longer driveable
Customer: replied 7 months ago.
Back pressure test?
Expert:  david craig replied 7 months ago.

yes. to see if the cats are clogged or partially clogged.

Customer: replied 7 months ago.
No i have not im gunna youtube it now lol
Expert:  david craig replied 7 months ago.

ok. if you dont have a backpressure gauge you can use a digital temp gun to check the inlet and outlet temps.

Customer: replied 7 months ago.
What temp am i looking for and do i need to be completely warmed up? But that dosent explane the 1 and 6 misfire?
Expert:  david craig replied 7 months ago.

yes completely warmed up. and it sure can cause the misfires. you said they were jumping around.

Expert:  david craig replied 7 months ago.

the outlet temp should be at least 100 degrees hotter than the inlet temp on the cats. make sure you aim it at the welds of the cat.

Customer: replied 7 months ago.
No ive allways had a 1 and 6 mis
Expert:  david craig replied 7 months ago.

do the back pressure test anyways.

Expert:  david craig replied 7 months ago.

i meant the temp test

Customer: replied 7 months ago.
Ill check it out first thing in the am ill have to pick up a temp gauge
Expert:  david craig replied 7 months ago.

ok

Expert:  david craig replied 7 months ago.

any luck?

Customer: replied 7 months ago.
No heat was good 100 over like you said im gunna test the wires going to the coil pack since 1 and 6 fire off the same coil
Expert:  david craig replied 7 months ago.

i thought you replaced that coil pack?

Customer: replied 7 months ago.
No never have looking like i need to but want to check the wires first i found some oil on the #1 spark plug should i br alarmed
Expert:  david craig replied 7 months ago.

was it in the spark plug tube or on the bottom of the plug?

Customer: replied 7 months ago.
On the bottom very light tho
Customer: replied 7 months ago.
i did a compression test and its in spec
Expert:  david craig replied 7 months ago.

did you do compression on all cylinders?

Expert:  david craig replied 7 months ago.

checking in to see how its going

Expert:  david craig replied 7 months ago.

hello??

Expert:  sprinkles08 replied 7 months ago.

Hello and welcome to JustAnswer!

It sounds like cylinders 1 and 6 may be down due to a loss of spark. You may have a bad coil, coil driver circuit or driver wire issue. Have you checked for spark on 1 and 6?