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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 9/15/2005 7:59:47 AM EDT
Folks, this is downright embarassing. My wife has an '02 Mercury Grand Marquis that's bucking and running rough. It's got just over 50K soft miles on it and I wanted to try changing out the plugs to see if that helps. Only problem is, I can't find where the darn plugs ARE. Yeah, I know it's got individual plug coils but I can't seem to find them when I look under the hood.

My Tundra has plug coils but everything's right out there where it's staring you in the face. Easy plug changes on the Toyota.

The Mercury?? Ok, call me stupid, a blind idiot, even take away my man card but I need some help here. Can anyone give me a clue as to how to find the blasted plugs on this 4.6L monster? My only alternative is to take it to the dealer and and pay out the rear for a 'simple' plug change.

Please, anyone that's done this before, what am I missing? Is it something obvious like you can only see them by the light of a new moon ??

Should I even dare to try and change out the fuel filter too?? Haven't even STARTED looking for that, let alone have a clue where it is.

I really HATE the idea of dropping hundreds of $$ at the dealer for routine maintenance items, but if that's my only/best option I'll suck it up and do it. HELP!!!
Link Posted: 9/15/2005 8:04:22 AM EDT
look up from under the car
Link Posted: 9/15/2005 8:22:51 AM EDT
[Last Edit: 9/15/2005 8:23:08 AM EDT by gsiebrecht]
On some cars you have to take the intake manifold off to get to the plugs, at least that's the way it is on my car.
Link Posted: 9/15/2005 8:37:54 AM EDT
I'll wager that it's not a plug at all, but a bad coil. Take it to a mechanic with the proper scanning equipment to get a proper diagnosis before you tear into the engine. This car has plugs that are good for 100K. I had the same issue with my F-150. Took it to the dealer to change the plugs at 70K, and the service writer, who I know, bet me the cost of the service that it wasn't a plug. Sure enough, a heater hose had a pinhole leak in it, and was basically shooting steam right on a coil, and cooked the coil. The coil was about $80, and maybe $45 labor. If they had replaced the plugs, it would have been over $600.
Link Posted: 9/15/2005 8:57:25 AM EDT
Would there be a diagonstic code if there's no check engine light?

And do I really have to crawl under the car to change the plugs, or just to see them??
Link Posted: 9/15/2005 8:57:39 AM EDT
Be glad that you have one of the easiest cars to change the plugs on made! Also buy a service manual ASAP.

Here is a quick description of whats involved!

They are on the top of the engine (you may have to remove the plastic cover) along the edges of the black plastic intake manifold. 1998+ GMs do not have coils and wires, they use COP (Coil-on-Plug) modules. These look like little round cans above each plug- they have a yellow label on the top of them so they can be spotted easily. Take out the 7mm bolt holding the COP to the intake and it will pull right out. Then you can get to the plugs easy standing by the sides of the car, the only interference is the air intake tube, it can just be unscrewed and set aside. You will need both 12” and 6” extensions and a torque wrench, the heads are AL and will strip easily – also wait to the engine is COLD. If you do not have a compressor get a can of compressed (the computer stuff) air to blow the plug wells out. Torque to 15 ft-lbs and gap to .054. Also make sure that you do not cross thread the bolts that hold the COPs to the intake or torque then to much.

To be honest I do not think it is you plugs, the COP modules go bad and will cause the problems you have. If there is a code go to an AutoZone and have it scanned it will tell you what COP is bad, then it is just one bolt to swap the COP out (10 min max start to finish).

www.crownvic.net is a good resource for both Crown Vics and Grand Marquis
Link Posted: 9/15/2005 9:48:13 AM EDT
WOW, thanks a bunch for the specific info. I've got all the hand tools and torque wrench's I need, just wasn't able to find the plugs..

There's no CEL (Check engine light), does that mean that an autozone scan is pointless?

$600 to replace plugs!!! my god!...that's even worse than I feared.

P712k; I'll start hitting that website, I tried a google search and didn't come up with much useful so hopefully the can help and I won't tie up bandwidth here with these types of questions...

If there's no code set, is my best bet to buy a new COP and start swapping it in and out until I find the offending one? I can handle $80-$100 to fix this problem a lot easier than $600!!!
Link Posted: 9/15/2005 9:50:47 AM EDT
I vote for the COP also. I think they go out at about a 4:1 ratio to actual plug problems on cars under 100K.
Link Posted: 9/16/2005 4:05:08 AM EDT
[Last Edit: 9/16/2005 4:11:31 AM EDT by p712k]
If there is not a code it is a little harder to determine which COP is bad. Swapping around a new COP will work but can be a PITA.

For how much stores/dealers charge (about $60.00 at NAPA) for one COP I would look on eBay, I have gotten a set of all 8 COPs brand new for about $150.00. Throw in 8 plugs for about $20.00 and for under $200.00 you will have a "new" ingition system that should last for 50K+. Make sure to use lots of di-electric grease inside the rubber coil boots. Also lighty wipe the OUTSIDE of the rubber coil boots with a rag with silicon spray on it , it will keep the boots from drying out and cracking from engine heat - this can cause misfires and make it difficult to remove them in the future.
Link Posted: 9/16/2005 9:45:55 AM EDT
It occured to me that perhaps I could get an idea as to which coil was causing the problem by looking at the plugs. I'm thinking of just picking up a coil this afternoon so that this weekend I can spend working this issue and have one on hand. Reason being, I live probably 30 min and 20 miles from the autoparts store and it's a royal pain to stop in the middle of a job to get parts...What do you think of this approach? I know once I buy the coil it's mine (no returns on elect parts) but it sure sounds like everyone's sure I've got a bad coil and I already have the new plugs so I can install them at the same time.

Also I looked at crownvic.net and there seems to be some debate as to installing plugs with or without antiseize??

Can't say just how much I appreciate all the help and advice I've gotten here folks. Thanks a bunch.
Link Posted: 9/16/2005 6:25:43 PM EDT
If the CEL isn't on yet, a scanner might be able to pull the pending codes. Ours will do it from the generic functions menu so a generic scanner should be able to pull them up. If ti is a real good scanner that can read the "Mode 6" data, it would be real easy to tell where the misfire(s) are.

If it is a bad misfire you may be able to tell which one it is by looking at the plugs.
Do not put bosch plugs in that car. I do not know why but it would be a mistake. We have fixed a lot of cars by replacing new Bosch plugs with Motorcraft plugs.

I would recommend always use a little anti-sieze on a plug going into an aluminum head. It probably does make it easier to strip out the threads if you really try. (Hand tite + 1/8 turn is all it takes)

Also, we have seen several cars/trucks that once they started would kill a differant coil every few months until all were replaced.
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