I have a 99 4.6L,auto expedition XLT 4x4
around a month ago I added some fuel system cleaner- ran the treated tank up but still wasnt getting "good" gas mileage like when I originally bought it.

I then installed new NGK V prong plugs from Summitt and oil /filter change. (the old plugs were way gapped out at 66000 miles)after initial rough idle the computer adjusted itself and truck ran great went on trip of 50 miles -ran great.

Here's where I could kick myself - the first fuel injector cleaner I used was not what I "normally" use and seemed to do nothing--so I went into auto parts the next day after the plugs were changed (buying something for another vehicle) and they had my duralube fuel injector cleaner on sale. I was thinking well it runs great but I always add this at oil changes with great results- cant hurt. so I added it to tank (this was 2 tankfulls after the last treatment)-- argggg instant miss started - then I noticed it said only treat once every 2000 miles! the miss is noticable under very light acceleration from a stop (slight hesitation) and when cruise control engaged and going up a hill/crest at highway speeds at around 1500rpms- the truck will lightly lurch a few times dropping in speed then cruise control will jack up rpms above 2000 and truck runs fine.

again the miss started as soon as I poured in the second bottle of fuel injector cleaner.

it has now been a few weeks and 3 tankfuls of nontreated gas later. yesterday I installed a new fuel filter and "reset the computer" (disconected battery for an hour) the miss is now not as frequent but still occurs under the above stated conditions.I emptied the gas tank to about 6 gallons before adding fresh gas (3 tankfuls)-- by now mathmatically there is virtually no treatment(16oz.) left in gas.(so many hundredths of an ounce- of cleaner per gallon)

maybe adding the 2nd treatment and the miss were a coincidence but the miss started instantly after adding?
any ideas where to look next?-- clean IAC? or? any particular sensor I could have screwed up?maybe I should scrap the ngks for some motorsport platinums?

also truck revs in neutral/park up to 1500 rpms without ever missing a beat(slowly accelerating to 1500rpms or quickly)--hot or cold.

also the miss while driving from a stop occurs sporadically wether engine hot or cold(10-20% of time).

the highway miss at 1500rpm up a slope I'm pretty sure always happens just sometimes worse then other times. any ideas?Thanks in advance

 

What codes are you getting?
I personally would trash those plugs and put Motorcraft Double Platinums back in it. These engines don't seem to like other plugs too well.
Also, If it has plug wires, put a new set of Motorcraft wires on it too.
Jimmy

 

DITTO the above. For whatever reason, the 4.2, 4.6 and 5.4 mostly seem to prefer Motorcraft plugs.

 

thanks when it started the next day after changing plugs that was my first instinct to go to dealership and buy the originals.

then I got crossed up because of just having added the injector cleaner and it might be the culprit(as soon as I drove out the parking lot I noticed the new hesitation and it had drove fine for 30 miles that day prior to going to autoparts/gas station on the way back home)

have you read other posts about spark plug problems/misses when changing from from factory to aftermarket? I know this is possible cause my 92 f250 doesnt care for regular splitfire plugs (although I never had a miss they only lasted 2 years and truck mpg was not good and acceleration was subpar) and these plugs cut the tip instead of the metal prong on the plug so theyre similar to splitfires (spliting the spark in half)...

I'm used to the older vehicles in that when they had a secondary miss it was always present whereas this miss comes and goes?
I always thought if you had bad wires or plugs that the miss will always be there in the firing sequence(once at operating temperature). -and carbs etc. could act up. this hesitation will be there at one stop sign and then gone for the next three... (while completely warmed up after driving 20 miles even)

right before I changed the fuel filter and reset the computer it once briefly threw a service engine soon code (dtc) but it lasted for only about 5 seconds and never reappeared- will it still store the code even if light doesnt stay on? if so I guess I'd have to wait until it reappears but since changing the fuel filter the miss is less and probably wont throw a code (this leads me to believe its in the fuel/air/secondary system or related sensors).... guess I'll try motorcraft platinums... thanks again.

 

those plugs are trash.

Install the copper motorcrafts.

I like awsf-32c for maximum power.

If you want them to last a long time, then go with the platnium as stated above.

JH

 

Sorry for pickin' brains.....

done hundreds of spark plug jobs (engine rebuilds, carb rebuilds etc...), this being the first with plugs mounted "on top".another excuse is I had taken out my rubber grommett in the spark plug socket cause they have a tendency to stay on the plug and pull your ratchet "setup" all apart and i haden't cracked a plug installing it in years....

with this job i needed the grommett (couldnt find) so I wouldnt have to reattach the wire on old plug to pull it out of it's chamber and basically have to many steps when youre garage is attached and youre talkin' with family and uhhhh basically I got distracted-- had dropped a plug in cylinder tunnel by itself (cause again I did not have the rubber grommett in socket and you cant hand start these plugs...) then musta went to bathroom or got a drink somethin to cause a memory lapse- and then put the wire on unstarted plug!! Daaaaaaaaa
Of course I didnt realize until I had bought ford's platinums at 7 a piece!!(thats a ridiculous price!) but oh well at least this time I found my pair of large needle nose pliers to remove them generic wires),a new socket and a 1/4 to 3/8 adapter to use my 1/4 drive to get a better "feel" and prevent binding- job took 1 hour 15 min. compared to over 3 hours the first time! this also explained my secondary missing one second and then not the next second later...
I still think the plugs placement is quite generic (my mistake wouldnt of happened on a side of head setup...) and only 3 full threads in - how ridiculous...

jfbranham if your miss sounds like mine throughly recheck/replace your plugs, clean wires (make sure theyre sunk all equally on plugs compared to one another) after that youll need an error code or take it in for analysis cause at 80 per oxygen sensor (x4) and 2 cop's its quite expensive.

now I have an extra set of ngk's for future, and in all fairness to ngk the pickup from a dead stop was just as good maybe a little quicker takeoff and that's with one not even threaded!!! so all in all I wouldnt hesitate to reinstall ngk's 50000 from now and will.

lesson: even when a job is routine avoid distractions, or maybe one should retire from car repairs when approaching 40's ? (loss of memory skills-haha) I WISH!
someone kick me..........

 

From what I have read, the Autolite Double Platinums are the same at the Motorcraft Double Platinums. They are $3.67 each at Advance Auto.