Changed out all plugs & two coils in my 1999 5.4 and now it's only missing when in fourth gear at speed's from 40-50 mph.
Before that it was missing in all gears.
It runs smoth at speeds over 55mph,around town I have to keep it in over drive so it will not buck.
I pulled the super chip and cleaned both computer and the chip,I thought I had it fixed but only lasted 20 miles.
I had the chip since new,do they go bad.
What else can I check.
Thank's JOE

 

You have a low grade misfire Joe. Keep those two COP you purchased as spares - Go to Global Automotive , purchase 8 COP's (DG 508'S) from Kevins store. You'll only pay $96 for all 8 together.

Install these at the same time to keep your 5fours integrity intact and you problem will go away .

It happens quite a bit and you can search this forum if you like . When the COPS get weak , there favorite spot to act up is 45mph (in the 5.4L) just before the shift into OD.

Heres the COP deal link -

http://cgi.ebay.com/ebaymotors/NEW-I...mZ160111254456

Make sure you cover all the bases and use Motorcraft Plugs (there OEM ) for best results.

You can check out Matts directions on a sparkplug change here -

https://www.f150online.com/forums/li...parkplugs.html

I'll add that you need a tube of dielectric grease and apply liberally to the insides of all COP boots (very important) Spark goes nuts inside the boots without grease and will carve a some carbon trails with a new COP system.

She'll feel like a different truck when your done

 

That person that sells COP's for 5.4 engines are they ok to use,I mean thats a good deal for eight of them,I spent $37.00 for one,I just don't want to throw money away on junk.
Is a low grade misfire a common problem with ford trucks.
I want to check a couple more things before that.
Where are these two parts located on my 1999 f150--5.4FICM harness andMass Air Sensor.
Thank's JOE

 

 

That COP unit on ebay is $199.00,not $99.00.
http://cgi.ebay.com/ebaymotors/NEW-M...mZ160147438952

 

Now they are , you waited to freakin long.. They were $96 for the last year and a half..

 

He has DG508's at all kinds of prices -

http://cgi.ebay.com/ebaymotors/NEW-I...mZ160147439372

How's $90 plus $11 shipping sound?