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2002 Grand Marquis

My wife has a 2002 Grd Marquis with about 100,000 miles. In the past she has complain about it shuttering or skipping when lightly accelerating on a hill or speeding up. I have change the spark plugs at about 40k and 80k and it seemed to help a little. When I change them at 40k it stopped all together for a while. It was a cool morning this morning (which I think it does it worse in the cool air) and she called me and said it was jumping (shuttering - skipping) at 70 mph all the time. I do not know a lot about the individual coils at each plug that this car has (maybe all newer cars have) but could one of these be the problem. I see on parts store sites they have coil connectors. Are these a possibility? Any ideas or suggestions? I’m a big do it yourselfer when I can. Thank you.

The AODE transmissions on these cars are notorious for torque converter shudder. Sometimes a simple flush an the addtion of a certain additive is enough to fix it. However if it’s bad you’re looking at a rebuild.

Based on my experience: Did you ever replace the plug wires? Nowadays, plug wires go bad as rapidly if not more so than spark plugs. Caution: there are a lot of really cheap plug wires out there, that are no good. I would get them from FORD, a premium set if they have such. It won’t be cheap. Or you could have a garage put it on a scope before spending this money. Regarding the cool, if it were damp and dewy this could make problems from bad wires even worse. If you change the wires, don’t forget the dielectric grease.

This car has no plug wires!

It can be very difficult to determine, SOTP, the difference between torque converter shudder and misfire. If it is constantly misfiring at 70 mph that should trigger the CEL. If the CEL is illuminated, get codes read. Does the shudder feel sort of like rumble strips on the side of the road? Has the transmission been serviced on this car every 30K as it is supposed to be done? What does the transmission fluid look like?

Note that if someone put something other than Mercon V in this 4R70W, it will soon be dead unless you get it out and put the right fluid in. Alternatively, you can get a couple of bottles of Lubeguard MV and add it.

Your car has “coil packs” and they can be VERY troublesome. They REALLY do not like power-washing…

Usually, you can force the issue by accelerating at WOT which will generally cause the CEL to come on. Then read the codes and see which cylinder(s) are misfiring. Replace the failed coil pack(s). I had a “random misfire” code on a '98 Crown Vic (same engine) so I found a set of coil packs on E-bay and replaced them all. Problem cured. All those Ford coil packs are the same 4.6-5.2 V8 motors.

You might carefully remove them all and inspect for water or anti-freeze in the plug wells, or degraded resistors which are located inside the plug boots. There is a tiny screw that holds each coil in place. Take care in disconnecting the primary wires until you figure out the clip. You may have to disconnect a couple of the injectors to make room, but they all will come out with a little effort. If you have changed the plugs, you already know this…These cars come with 100,000 mile platinum plugs and normally they will go that distance trouble-free…

These cars DID have an issue with torque converter judder, a funny vibration that is sometimes mistaken for mis-fire…Changing the tranny fluid usually cures that problem…A true mis-fire is almost certain to make the CEL to come on, but a light misfire will sometimes be tolerated by the computer for a while…

That car does not have “coil packs.” The early 90’s models did. This car has COPs, (Coil on Plug) eight of them to be exact. Yes, washing the engine can get water down around the plugs under the coils, and will cause misfires till the water boils off. Do it enough, and you may damage the coils. My bet’s on the transmission, if it wasn’t flushed every 30K miles.
I see “coil packs” misunderstood a lot. Coil packs are packs of two or three coils together that have wires that go off to four or six spark plugs. COPs are a signal coil that sits directly over each plug. They have a boot, but no plug wires.

I drove the car this weekend and really got a chance to feel it. Cruising on interstate when starting to go up a hill it does feel like rumble strips. That is a very good description. If I would accelerate and make it drop to 2nd it goes right away. The transmission has not been serviced within 30k. As far as service does it need a complete flush and fill (with machine) or just dropping the pan and changing pan fluid and filter sufficient? Since the 2002 does not have a TC drain so I assume a machine is required. I know it does have Mercon V. I did service it by dropping the pan and changed the filter about 50k ago. It is due service but to what extreme? Thanks for your help.

Yes, get the flush by machine.

IIRC, it was partway through 2002 MY that Ford decontented the TC drain plug so you might have one. You can pull off the plastic plug, turn the TC around with a lever and look. If it does have one, you can drain the TC and drop the pan. If not, I think a machine is best. The pan should be dropped, filter replaced and pan cleaned in inspected for big chunks even though I think Ford no longer specifies anything beyond flushing. Good chance a fluid change will fix it. If you are going to do it yourself, check out:

Unfortunately, it looks like you might have to register, but it does not cost anything.

I have the exact same problem, rumble strips feeling when driving up hills, in my 2009 Grand Marquis?
It seems more like a suspensions/tires problem. Im ruling out misfires/sparkplugs/coils/gas-pumps as RPM stays constant throughout, I think!

any conclusion?