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Check engine light mystery

2004, 100k miles, check engine coming on, off since February. Dealer cked several times, from their invoice: “Code P0303 Cyl 3 misfire, swapped coils and miss follows the coil, coil is bad. #3 ign coil bad, replaced #3 and retested all working normal, cleared code.” Came bk on, mechanic cked, his invoice: “Code scan P0303 cylinder #3, pull codes from computer, document code, run chart to find source of code. Pulled 2 more coils on drevers side, compared resistance between #3 and coils 1 and 5. Resistance read good, 1.6 to 1.7 ohms. Ignition coil replace one (B). Plugs look new.” Dealer says replace PCM. Mechanic says rough idle might be triggering it. Ask a Mechanic on this site suggested a leak down test or decarbonize engine. Done, ck engine light still on. Car drives fine as far as I can tell. Help please!

Your, question. Is, about as, clear. As mud.

read it. don’t get it.

Alright, well, it sounds like the mechanic isn’t finding the problem.

So let’s start from square one. Take it down to an Autozone and get the codes read. Let’s be sure the mechanic didn’t write the wrong code down. Report back here with your findings.

It sounds like you are going back to the same people time after time. Maybe you should look for a different mechanic (Independent mechanic) and give them your history and the car so they can take a real look.

Having said that, dealer may be doing OK but it would be difficult to tell from here. However someone here may will have run into this and can give you better guidance.

BTW I tried to read your question, but I kept getting lost. Paragraphs usually help.

I will go to Autozone and have them get the codes.

You Didn’t Mention Spark Plugs Or Spark Plug Wires.

Have either plugs or wires been replaced at some time ?

Do you have a normally aspirated (non-turbo charged) 2.4L engine in the 2004 Liberty ?

The reason I’m asking all of this is that Chrysler came up with a new spark plug recommendation for some 2.4Ls normally aspirated (non-turbo charged) that is more resistant to possible cold engine fouling (must have been a problem). Included are 2002-2004 Liberty Models.

If you’ve got the originally installed and / or recommended RE14MCC5 plugs then I’d install the now recommended RE16MC (.040" gap) plugs.

To prevent possible high secondary ignition voltage flashover, Chrysler says you should also replace the ignition cables (plug wires) the first time the plugs are changed (from old style plugs to new style).

What ?


Went to Autozone this weekend and their report said:
Cylindar misfire detected, cylinder number 3. Explanation:
The powertrain control module monitors the crankshaft speed and has detected a misfire condition. Probable cause: Ignition system fault-spark plugs, ignition wires, coil. Vacuum leak. Injector fault. High or low fuel pressure.

Early in this process, the dealer replaced an ignition coil and the spark plugs. After that, an independent mechanic replaced the misfiring ignition coil, did a leak down test and a tune up.

Autozone didn’t say they thought I needed to replace the PCM just that if I did, I could get a reconditioned PCM and install for $500.

I will have to check the owners manual to answer the question about the “normally aspirated (non-turbo charged) 2.4L engine” posted by Common Sense Answer.

My next step is to have the mechanic recommended by Autzone look at it and sort out what is next unless you would otherwise direct.

Thank you!

The next time you go there, don’t come away with the text, come away with a code: in this case it was most likely P0303. The codes associated with a check engine light are always a P followed by 4 digits.

What is the status of the spark plug wires?

Has anyone checked the fuel pressure? Has anyone checked out the operation of the fuel injectors? If there is nothing wrong on the face of it, someone could swap the #3 injector with another injector to see if the misfire follows.

The code was P0303, I am sorry I meant to include that.

Will have to ask regarding spark plug wires, fuel pressure and injectors.

On the invoice from the dealer, it indicates the misfire did follow the coil:
“Code P0303 Cyl 3 misfire, swapped coils and miss follows the coil, coil is bad. #3 ign coil bad, replaced #3 and retested all working normal, cleared code.”

So did the old coil stay on #3 or did they swap them back. If one went it wouldn’t be so odd for another to go. So, e.g., if they swapped 1 & 3 and left then that way, then replaced the bad one now on #1, then the original #1 may now be bad. Long shot, yes but possible.

Another option is worse. Sometimes a bad coil can damage the PCM. The the damaged PCM can keep taking out coils. Its probably worth having that looked at.

last installment. Third mechanic did a compression test. Zero in first and third cylinder, 40% in another. He says head gasket replacements in order. And, that he doesn’t see how a leak down test could have been done as a previous mechanic said if cylinders have no compressin.