I recently bought an 04 Lariat Crew Cab with 56k miles auto trans and 5.4. Before I bought it I complained that it had an exhaust noise, an acceleration issue at 40 mph and 1100 rpm’s and the ac was not very cold. They replaced the exhaust manifold on pas side, the coil pack on the #3 cylinder, recharged the AC, did a tranny flush and a flash drive update. It seemed to fix the problems for the most part but I drove mostly 30 mph or less to and from work. I took it on a few road trips on the highway and country roads (40-60+ mph) and noticed the problem again and it became more consistent. It happens pretty much all the time when ac is on and overdrive is on between 40-60 mph and after decelerating and slowly accelerating. Less noticeable or less consistent with ac off and have never noticed it with over drive off under the same mentioned conditions and mph range. It feels like a limited slip kicking in or driving on dry pavement with 4wd on when it happens. The tranny shifts fine in straight acceleration pulls through all gears and even full throttle pulls. Problem only happens after decelerating and slowly accelerating. Any thoughts? Brought it back to dealer but the tech could not get it to repeat so I took him for a drive and he thought it might be another coil pack. The 60 day warranty is history so I don’t feel like shelling out $$ for them to tell me what they think it is!

 

Did you ever solve this problem? My 06 has gone through 4 coil packs and plugs.. it's not fixing it. If you gently touch the gas at about 50-70 mph the bucking starts. Help I am out of Warranty!

 

Anyone else have this problem or know of a solution?

 

Here is the general info on such a 'specific' missfire.
When in those driving conditions the EGR is opened by the computer to let some exhaust gas back into the intake.
The ignition timing is advanced and fuel is cut back.
This results in a very lean mixture in the 20 to 1 range.
A lean mix requires much more spark voltage to fire the plugs .
If one coil has low output "under those driving conditions" a miissfire/stumble results.
As soon as the driving condition changes that cause the EGR to close, the missfire goes away.
This cancels a pending code for that cylinder because the condition has cleared. (Not a hard fault)
Bottom line is a coil is ususally the cause with shorted internal turns in it's winding.
It may be posible the EGR opening is more that it should be or letting to much exhaust gas return to the intake.
It's a toughy to get hold of but now you know the basis behind the cause.
Good luck.

 

Bluergrass, your explanation makes perfect sense. The missfire went away when I pressed harder on the gas too.
So I took a chance and I replaced all of the coils on this truck that were not new. Two had been replaced by the dealer but then my warranty ran out, so I went here and bought 6 new Accell coils:

06 2006 Mercury Mountaineer Ignition Coil - Engine Electrical - Accel, Delphi, Denso, Karlyn, MSD, Motorcraft, Prenco, Standard Motor Products - PartsGeek

This corrected the problem immediately. When I lightly accellerate the problem is not there. It was happening only when the engine was warm too, which I think has something to do with when the EGR opens.

So all fixed, go buy the coils and replace them yourself in under an hour!

 

Great to hear but the coils you chose are not very good over the longer time period.
They are made in China.
Expect to have issues again in the future with these coils.
Glad it proved the trouble but the coils can be bad actors later on, so good luck with them.
At least you know about it.
I have been there with these coils, that why I am replying about them, as a heads up.
Take care.

 

Thanks. I've got 60k on it and plan on driving to about 120k so maybe ill get 60k out of them. We shall see! Certainly the stock Motorcraft ones that cost 73 bucks didn't get me far, so I wasn't going to buy them again...

 

You most likely need a set of spark plugs. The early design plugs are terrible and the gap widens very fast. I have pulled plugs with only 60k on them and the gap was over 0.070". The Motorcraft SP 515 plug is a lot better design and should solve your problems. The life of the coils will be shortened with worn plugs because it takes a lot more voltage to jump the gap and the spark duration will be shorter.

 

Lets put it this way, the OEM coils are the best your going to get for quality and average life.
Since they are used from the factory, any other coil is of unknown quality, so the OEMs are the standard.
Realize that the coils live under very harsh conditions of heating and cooling from the heads, heat from the radiator and heat from the exhaust manifolds just after engine shutdown.
Like any other part, they are expendable over time same as tires and shocks.
You will replace most tires sooner than coils with their higher cost and think nothing of it , discounting exceptions to that like anything else.
Good luck.

 

I think this is the best I have ever heard someone explain the cost of the OEM coils. Well done sir!

I could not agree more with this post!

 

Let me add something that may be of interest.
Any other coil has no real life history by compairison to the OEM units..
Buying high output coils in the hopes of gaining power will never happen on a stock motor.
All a coil needs to have is enough reserve voltage to fire the plugs under the worst conditions of EGR operation and erroded plug gaps to a reasonable degree before some type of service is needed.

To have higher voltage available from a coil is of no benifit.
The reason why is as follows:
Under normal air fuel mixtures in the 12 to 15 range, the voltage needed to fire accross the gap is always a function of the mixture density and to some degree cylinder pressure.
This requres in about the 7 to 10,000 volts range.
When the EGR is called to open, the mixture goes up to the 20 to 1 range.
Since this results in less density in the gap area, it requires 20,000 or more volts to cause the spark to jump the gap so you see voltage requirements go up drastically.
Here in, if a coil has low output, a missfire results as was the OP case above.
Bottom line is high output coils above about 40,000 volts on a fault free motor has no benifit.
To finish with a possible qustion that is often asked. If the plug only needs 7 to 10,000 volts to fire a normal mixture, what happens to the rest?
At the time the spark jumps the gap, the low resistance offered in the Plasma in the gap shunts down the coil output such that the voltage cannot rise any higher than the breakdown value and is lost.
This means the absolute voltage required is density dependent.
Installing coils of any higher output than what is needed withsome reserve has no benifit.
Power comes from the BTU content of the fuel in any given motor design.
Good luck.