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Ron
Ron, ASE Certified Technician
Category: Jeep
Satisfied Customers: 35289
Experience:  34 year working in the automotive field as a Tech.
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I just bought a 2003 jeep liberty limited 3.7 with 126k.

Customer Question

I just bought a 2003 jeep liberty limited 3.7 with 126k. before I got it home the check engine light came on. it had a po302 code. I changed the coil on the 2nd cylinder and added some sea foam. but the code keeps coming back. I have driven over 300 miles. light usually comes back on around 160 miles later. sometimes the light is flashing, then it seems like the engine runs rough, but if I clear the code it runs fine. any suggestions. I like in ny and need to get it inspected soon.
Submitted: 5 months ago.
Category: Jeep
Expert:  Ron replied 5 months ago.

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

Expert:  Ron replied 5 months ago.

Jenn ,

The check engine light flashing means the computer is seeing a direct engine misfire on this cylinder. When you changed the coil did you also change the spark plug?

Customer: replied 5 months ago.
No the plug looked brand new
Expert:  Ron replied 5 months ago.

I would still try swapping the number 2 spark plugs with the number 3 spark plug and see if the misfire moves. If it dose then the spark plug is breaking down. You can do this with out having to replace any part just to see.

Customer: replied 5 months ago.
I will try that
Expert:  Ron replied 5 months ago.

As I am sure you know in order for the engine to fire all cylinders you need good spark, injector pulse and good compression. If the coil is new and the engine runs on all cylinders then in most cases this type of misfire is usually caused by a failing spark plug. Swapping them over will verify if in fact that is the case. If not let me know and we can work from there if need be.

Customer: replied 5 months ago.
switched the plugs, code is still pending,, may just need to drive more
Expert:  Ron replied 5 months ago.

You can clear the code by disconnecting the negative battery cable for a few minutes and then drive it and see if it resets.

Customer: replied 5 months ago.
light isn't on,, but code is pending... won't pass inspection yet
Expert:  Ron replied 5 months ago.

Okay then you are going to need to drive it for a while till the drive cycle sets.

Customer: replied 5 months ago.
in the past after I clear codes the light comes back on after driving 100 miles or so
Expert:  Ron replied 5 months ago.

Okay while you getting the drive cycle to set lets see if in fact the light returns and if so what code comes up.

Customer: replied 5 months ago.
it is still a 302 code
Expert:  Ron replied 5 months ago.

If you where able to clear the code and your sure the spark plug as well as the coil checks okay then that only leaves checking the injector and or checking for a vacuum leak which could cause a misfire on that cylinder.

Customer: replied 5 months ago.
how do you do that
Customer: replied 5 months ago.
the coil is new
Expert:  Ron replied 5 months ago.

The best was to check the injector is to swap it with the injector from #1 and or #3 cylinder just like the spark plug and see if the misfire moves. To check for a vacuum leak you need carefully spray added fuse such as carb cleaner in and around the area of the #2 cylinder looking for any difference in the way the engine runs.

Customer: replied 5 months ago.
misfire doesn't move I do't think there is a vaccum leak
Expert:  Ron replied 5 months ago.

Okay in order for the cylinders to fire you need good spark to the spark plugs, injector pulse at the injector and proper compression. Since the misfire comes and goes and you are sure the coil and spark plug check okay thent he next step would be to check the injector by swapping this cylinder with one of the other cylinders and see if the misfire moves.

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