engine hesitation when maintaining a speed

Asked by May 01, 2012 at 05:28 PM about the 2003 Mercury Grand Marquis LS Premium

Question type: Maintenance & Repair

I have a 2003 grand marquis with 90,000 miles, when I am maintaining a speed I feel a jerking sensation. I thought it might be old spark plugs and an old fuel filter so I changed both of them out. But I am still feeling the same thing.  Does anyone know what the problem is?

16 Answers


If you tuned it up with new plugs and plug wires then it sounds like it coud be some bad gas and/or dirty fuel injectors. You'll usually notice a bad injector at a higher rpm when there's more of a demand for fuel. There's one for each cylinder on that 4.6 motor. Try a couple cans of Gumout fuel injector cleaner in the gas tank to see if that helps clear it up. If it seems a little better , do that a couple different times, otherwise you might be looking at some fuel injector replacements and they aren't cheap. I don't remember if that car has separate coil packs or not, I believe it does. if so, you might have a bad coil pack too which would make it cutout at high rpm. Take it to an Autozone parts store and see if they can put a scanner on it, that should tell you what's bad and they test underhood stuff for free. Good Luck. Kenny.

8 people found this helpful.

first thing you need to do, is a scan for trouble codes. sounds like a cylinder miss fire. could be that one of the Coil Over Plug (cop) is bad. a quick scan can verify an issue.

6 people found this helpful.

Could also be a torque converter solenoid starting to go bad. At speed it's supposed to lock it in, but if it doesn't it'll almost feel like the transmission is slipping a little.

14 people found this helpful.

I'm having the same problem. All coils and plugs have been replaced. Seems to be most noticeable around 50 mph, in high gear, under light to moderate acceleration.

30 people found this helpful.

Dont have an answer but my 05 mercury doing it too I get the same codes when they check it I changed the number 1& 2 cylinder plugs and it says sumn bout either a throttle problem or intake problem. I put a can of sea foam in my tank and filled it up and a half of can in my crank case to clean my injectors and engine block out it cleared up for a few minutes on the highway thr check engine light went off but whenI got off highway 95 came to the stop sign and gave it a little gas it was still skipping

4 people found this helpful.

This engine is known to have this problem. Mercury/Ford put out a notice but no recall. I have an 01 marquis that we already replaced one spark plug with an insert but #7 also needs replaced. From what I've read, the aluminum wears over time so it needs tapped out an insert put in and then put spark plug in.

8 people found this helpful.

My 2002 with 4.6 also has this issue, but I notice mine during light acceleration but only when weather get cooler (30 to 40 degrees) and misty out it will hesitate so bad I swear it's gonna drop the drive shaft. I've had into my local shop twice and naturally it wouldn't do more were there any codes.

8 people found this helpful.

Bob, if it happens when the humidity is high you can try using a windex type spray bottle to spray around the coils and it may act up. the boots on the coils act like plug wires and can degrade over time allowing the high voltage to "trace" away from the plugs. Your vehicle also supports mode 6 data that can store data that doesn't set the mil off. Mode 6 requires a more advanced diagnostic computer than most shops have. The Ford diag computer should make quick work of it.

5 people found this helpful.

I have a 2004 Mercury Marquis with 75000 miles. I am getting the same hesitation.Took it to Autozone.They told me put some heet in it to see if it was water in gas. Then had them check for a code but check engine light was not on, so nothing came up. Bought some Lucas injector cleaner and put that in. I need a check engine light to come on to see what coil is bad to change it out. Hate to change all coils and plugs out if dont need them.

3 people found this helpful.

Hey Thomas did the Lucas injector work did it solve the problem

3 people found this helpful.

Run the codes if u get cyl 4 7 misfire they are usually the worst they get most stress ir anyother cylindet misfire swap the coil packs with a cyl that never hesitates other than 4 or 7 if it follows change the packs.. I have a diff issue lately a real stumper with the ac on only every 20 seconds at higway speed trys to shift rather violently then back normal then 20 sec again for as long as the ac is on so far im guess somthin in ac but just thought id put out some bait and see if anyone can help me out damn these cars are awesome tho right love mine

2 people found this helpful.

Put a dab of di-electric grease on threads of plug, spring connector in boot, and two wire connector at top wipe of excess on two wire connector it will short if not use a artist paint brush to apply there. On the threads it will stop it from seizing, and tearing out the threads, saves big bucks.


Redman, that's funny bc when I got mine the ac blew super hot air no matter what. Watched YouTube video on how to bypass temp control module bc they are crap I these cars and known to cause this issue. It worked and my ac has blown super cold air for about 2 months. In this time starting about 4 days or so, my car started just dieing out of the blue while driving. Always if I've stopped at a light or am just starting to pull off from making a stop. Very random! It gradually has gotten worse! Now at low speeds accelerating usually between 30-50 it shutters or kicks hard! Doesn't stall out as much now but it really struggles and kicks when accelerating at low speeds. If I gun it as soon as I take off I can usually get to my desired speed without car kicking and feeling like it's going to die on me. It's got new MAF, TPS, fuel filter, fuel pump less than a year old, valve seals, oil, tranny fluid with Lucas in it for stop slip (good for old tranny's) i cleaned the ICU already and the injectors, new valve cover gaskets...the car has 201k miles but the engine is a replacement before I got it and only has maybe 56k miles on it. WTF y'all?! And just 3 days ago all of a sudden my account kicked back to blows extremely hot air right about the time that it was really kicking bad on my and I stopped. To restart car. Idk how this could have happened bc I set the module to cold and then disconnected the power from it so it wouldn't switch back to hot!? I've been running circles trying to figure this issue out but I'm just stumped. Also when it started kicking and dying randomly I got a running rich code but that was right after I put an injector cleaner in my tank so I assumed it had something to do with that and didn't pay any mind.. if anyone can point me in the right direction I would so very much appreciate it! Tia!



1 people found this helpful.

2003 Mercury Grand Marquis. 238,000 miles. The car jerks when I gently speed-up from about 50 mph. I have used gasoline additive Lucas 3 different times. No luck. I have purchased full tanks of gasoline from 3 different gas stations. No luck. I have tried not using overdrive. No luck. Replaced fuel filter. No luck. I have opened the hood at night in the dark looking for an arching spark. No luck. I'm trying to determine if it is a coil/spark problem, fuel problem, or transmission problem. Next, fuel pump pressure test. I don't think a fuel pump would give me a 'grace period'. They either work, or are junk.

Dude, spend the 80 bucks, and order all new coils from amazon and buy new spark plugs, then take the 45 minutes and put them in....it'll be like a new car...trust me....I've done that with my girlfriends THREE Merc grand Marquis's....

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