I have replace plugs, 7 of the 8 coil packs and boots, egr valve, and some other smog valve on front of the valve body and still have a bad miss...Everytime i replace something it runs great for about 30 or 40 miles and then goes to missing at 40-50 miles an hour...I have changed the fuel filter.. I don't know what else to try.....any ideas..... 4.6 motor

 

check the fuel system. The fuel pressure regulator might be your culprit or the fuel pump. Time to do a pressure test on the fuel system.

No codes?

 

pay the 75 dollars for shop to put it on the machine and identify the issue?

 

If that was my truck, I would bite the bullet and take it to Ford.
Sure it's expensive, but they have diagnostic equipment and tech papers other shops have never heard of.
Time to call in the experts.

 

timing may be off?

 

the only code i have gotten is EGR which I have replaced. I put my Scan Gage II on it last night and that's what i got. I cleared the code and have driven it today for about 30 miles without misfire....no code...but i know it's coming...I don't mind paying the $150 for the basic check, but a lot of times they don't get anymore than I do with my scan gage the mech. told me..My son works at a shop and he put thier comp. on it and got the same code..EGR..he also thinks it might be fuel pressure..I am going to get the last coil on this weekend, it will take all weekend at my speed, and see what it does if anything. It's the last one on driver side under the firewall...can't wait for that! Thanks for the input...

 

i had the same problem, it could be your cylinder gasket leaking, thats what mine ended up being after i replaced my coil pack a million times

 

You had an EGR code? Did you check the EGR sensor? I would bet a dollar to a donut that it's there. Those sensors screw with these Ford's a lot. I'd check that before I put another dime into the truck. If it sends a false reading your EGR will set a code, and cause your description of problems. Also the vacuum hose to the sensor can be cracked and give you a bad EGR code. Check there. Good luck

 

I thought about the vacume leak, but if that was so wouldn't it miss all the time at any speed....

 

Hey. Long time ago on an older Ford I had the same problem. Turned out to be an O2 sensor that didn't throw a code. Check or replace those.

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