1998 F150 4.6 to 2002 5.4 swap
Kept the 98 PCM and Coil Packs
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- Initial start up; idle was PERFECT only ran for 5 minutes when it ran out of fuel.
- Everything was connected except exhaust (straight header)
- After pumping 2 gallons of fuel and driving it down the block it slowly got rougher, then stalled.
- I bolted up the new catback with all 4 - O2 Sensors and it seem to be missing an not wanting to idle :
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Here's whats going on now:

http://www.youtube.com/watch?v=DVLXNn1HxWI

 

I did your exact swap combo. 98 4.6 02 5.4. You need to double check the MAF (Mass Air Flow Sensor) It's on the intake tube. The IAC which is on the throttle body. I had a sort of similar problem with the idling. it would do this funny loop then die. I had the IAC on backwards. I put it on the way it made sense but it was reverse of that.

 

did you get a tune done?

 

Tune wont' do that. I'm running on 4.6 tune. For at least 8k miles. runs just fine. NO CEL's.