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?

11 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.

7 of 7 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.

5 of 5 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.

13 of 13 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.

22 of 22 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

2 of 2 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.

7 of 7 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.

5 of 5 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 of 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.

1 of 1 people found this helpful.

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


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

1 of 1 people found this helpful.

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