You need a code reader by ACTRON. It is the cheapest, and the best. get
the $200 one because it tells the codes and also is able to tell you
what each sensor is reporting, while the engine is running. This lets
you compare it with normal values, lets you campare the new part you
put in with the value from the old one, and lets you become experienced
with the proper operation of the systems on the car. It really is
simple, once you get the hang of it. Without this information you feel
like it is impossible to fix it and give it to a mechanic or a dealer
and get ripped off. With the scanner you know what is wrong, and any
new car you get you can also fix because they all work on the OBDII
system now and are very similar. All engine manufacturers have to solve
the emissions problems in similar ways, because there are only so many
ways to build a piston engine, and the principle of operation is the
same. Besides, you will make lots of new friends with your new toy, and
feel good about being the neighborhood "man in the know". You can also
do what I do, and supplement your income by buying cars with problems,
cheap, putting on your meter and diagnosing them, fixing them and
selling them or using them yourself. I taught my kids how to do this,
and they all got steals of a deal on their cars, and now fix their own
cars themselves. This is worth many thousands of dollars over a
lifetime.  Give a man a fish and he will eat one meal, teach him how to
fish and he will eat for a lifetime.

If you are looking for a lot of functionality from a scan tool for a
small bit more than the cost of a code reader, then search ebay for an
OTC Monitor 4000 Enhanced.  Don't confuse it with a 4000E.  The
'enhanced' version is slightly better -- at least in the cable setup.
It should come with domestic cables and you will need to be sure it has
the OBDII cable and at least the 'Generic System Smart Insert" which I
believe is P/N 3306-01.  This insert will cover Ford, most GM, and
generic OBD II.  Other inserts are available for Chrysler, ABS, etc.
You may need to find a used Pathfinder 99 cartridge to communicate with
your 98 F150 if the kit has an older version.

This tool will open up your eyes to EFI diagnosis if you've never used
one before.  They should be going for cheap too, since the Monitor
platform has been dropped for the last few years.  It's great for
domestics and is virtually worthless for imports, FYI.  You will be
able to get into more than just the PCM on most domestics.  Typically
there will be ABS and airbag coverage as well.  Sometimes it requires a
special cable or insert, which are relatively cheap.  You can control
motors and solenoids with bi-directional control on many different
systems.  Makes a dandy generic code reader, too.

Toyota MDT in MO