coil and spaek plug replacement

Asked by Jan 10, 2015 at 10:47 AM about the 2004 Mercury Grand Marquis

Question type: Maintenance & Repair

check engine light on, and car runs rough

12 Answers


Buy some throttle body cleaner. Clean your throttle body and Idle Air Control valve. If no idea how to clean, replace the IAC. I think they are around $50. Here is a video on how to clean the throttle body: If no change after cleaning, you may need a new EGR also.

8 of 8 people found this helpful.

Have your codes read for the check engine light. Post the numbers back on here so we can better help you figure out its issues. If in USA some auto parts stores will read the codes for free.

2 of 2 people found this helpful.

The code came out to be misfiring cylinder 1 and 2

10 of 10 people found this helpful.

Did they fix it or do you now have to buy new coil packs?

4 of 4 people found this helpful.

Don't know if it's coil packs or not.that's my question

3 of 3 people found this helpful.

The trouble with error codes is that they don't usually pin point the problem. It will say "misfire" on cylinder one or two. Okay, so I have a misfire. The problem is it never says, "Misfire due to spark plugs". It now becomes a guessing game on what could be causing the misfire. It could be vacuum leaks, bad EGR, dirty injectors, clogged Cat, bad coils, bad plugs. Now you are faced with testing or replacing each possible bad part. That's why when you take it to a shop they will say things like, "we got a misfire code so we replaced XY and Z". Then a week later the check engine light comes back on, with the same code. Sometimes it's more than one component that can fail, giving the misfire codes. I am driving around right now with 6 error codes on my Camry. Toyota gave me the "we don't really know what the cause is, so we will have to start tearing everything off the car to find it." I said, yeah, no thanks. You will run me up $1000 in labor. I then drove my car from Las Vegas to Montreal. I made it with no problems....but I still have all the codes that I will figure out for myself. If I were you, I would take the error code, for example PO302, look it up in the internet, write down the causes, and just start testing or replacing the needed parts. Otherwise, you will just be paying someone $85 an hour to do the exact thing you will be doing.

4 of 4 people found this helpful.

Yeah i have been down this road before.thought maybe I would get lucky and there would be an exact needs state inspection as of 2 days ago so I'm kinda scrambling.hard to work ,plow take care of house and work on vehicle in sub zero weather with 5 ft snow as I'm sure you all know.on top of that my check engine light came on in my 07 f150 on my way home from work today.but thanks for the advise


its not a guessing game. the codes give you a general indication of WHERE the problem exists. The rest requires researching probable causes and testing the components. This is a process of elimination. Each component you test will reduce the list of probable causes until you come to the likely culprit. for example, a P0301 code on a grand marquis is a cylinder 1 misfire. once you know this, you have to start testing the components involved. There is the spark plug, the coil on plug, and other components that could contribute to the issue. each has to be tested and eliminated. its the same process the mechanic will use at any garage for 50+ dollars per hour. Never try to fix your vehicle by "guessing" what the problem is. Thats a waste of time and money. If you have the patience then all you need is the proper tools to help diagnose the problem. Its a great way to get to know your vehicle and take pride in maintaining it.

1 of 1 people found this helpful.

Like I said, error codes never give a definitive answer. A process of elimination is just guessing on where to start. If you have a list of 15 possible causes, aren't you pretty much guessing on where to start the process of elimination? I realize it gives you a general direction. Testing various components also takes various tools and gadgets. All of which add up very quickly. I'm not saying that you'll never figure it out. How many times have you heard people say that they have brought their car to the shop, and they've spent $400 on repairs and still have the same problem? That's because the shop doesn't want to spend the time and effort to go through all 15 items and test them all. They just guess and throw parts at it. I just wish that the code systems would narrow it down to a specific issue instead of a whole laundry list.

2 of 2 people found this helpful.

Where is cylinder 6 on a Mercury grand Marquis 2000 model

5 of 5 people found this helpful.

Here's the firing order.


Mercury grand marquis facing the car, starts from left to right 1--5 2--6 3--7 4--8

2 of 2 people found this helpful.

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