I have a chance to buy a 98 f150 ( long bed /2 wheel drive ) it has a 5.4 motor was told it was blown . what motor can I put in it's place since I hear the 5.4s can be trouble some ?

 

Without doing anything, but dropping an engine in, you can place the 4.6 1997-2000 or 5.4 1997-1998 from an F150/Expedition. (Yes the 4.6 was in a car before those years, but the engine is for a car and not a truck as the cam is different for HP and TQ)

Now if you want to place the newer 4.6 PI type Romeo F150/Expedition (Look for a 2001-2008 engine with D24D on the block above the passager exhaust front of the engine on the head or the 5.4 PI same place as the 4.6, but PI wrote on the block 1999-2003 F150-F250/Expedition or the E-van up till around 2014 ) you will need to change the engine wiring harness as this type engine has two different plugins on them and the non-PI type does not. Here is where you have to make adjustments as well if the engine comes from an F250 as the intake inlet tube for air and the throttle body is set differently and you need an intake for the F150. The throttle body gas from the pedal is placed differently and the air inlet.

You will need a different intake as the inlet tube for air and the throttle body is set differently on the Expedition as well on the 4.6 Romeo 4.6 D24D, but the F150 is okay.

The two plugs are the head temp sensor and the knock sensor which takes a different style plugin than the older engines and some 4.6 engines have two knock sensors as well.
The newer engines do not have a butterfly valve on the lower intake and that plugin is not needed.

Not hard to do to place either engine in your truck, but if you want more out of one of these engines it can be done on the HP/TQ side. I just looked at a 600HP 5.4L 2v F150 modified in 2001 truck that is bad to the bone inside and out.

 

In short, a 97-98 F150 5.4 is the non-Performance Improved version and would drop right in. I’m not sure what you feel as troublesome about this truck’s 5.4, though. It’s the 04-later that have the various timing system issues and ‘04 through at least part of ‘08 like to hang on to the spark plugs too tightly.

Also, between like year 4.6s, the cams are the same between trucks and cars. Not enough power difference for that itself (intakes, exhaust, computer tunes are the difference) to be a difference. It’s not like one has a Honda S2000-like 8,000 RPM torque peak and the other is a Cummins K19 with a 2100 RPM redline here.