Has anyone done the swap and had this problem? the 4.6 was running fine in Dec 2012 when I initially removed it (other than a bad head gasket and no CEL codes). I reused everything except the 5.4 shortblock is from the junkyard. It will fire up and then die unless I pump the gas pedal. I can keep it on idle around 800 rpm if I continuously lightly pump the pedal slowly. If I mash it to half throttle or more, it will slowly rev while stumbling and after-firing until it gets to 2000 rpm then it smooths out and will rev instantly from 2000 to 4500, but it will die if I don't tease the pedal. No smoking, and no CEL has occurred.

 

CEL on?

You used your pcm and original ignition?

 

Have you done a fuel pressure test? How old is the gas? any chance it got water contamination? sounds fuel system to me..

 

exactly....More info needed to further help you.

 

That shouldnt be a problem. It should run on the 4.6 tune. Needs a custom tune really but it will run.

 

I just now got notified about the replies to this thread. my email has been acting up lately. thank you all for the responses. it turned out to be a large hole in the brand new manifold I had to plug. its running good and idling fine now. Thanks again

 

It finally threw the lean bank 1 & 2 code before I plugged the hole. Yes I am using my 4.6 pcm and harness.