There are many causes to this problem, in a 1999 Ford Ranger 3.0L. It is usually caused by a spark plug firing when its not suppose to, or late/delayed timing.
Timing or lack of fuel
The timing for the 1994 Ford Ranger XL with a 2.3-liter engine is set at 10 degrees BTDC (Before Top Dead Center) at idle. The firing order for this engine is 1-3-4-2. The spark plugs should be connected in that sequence, starting with cylinder 1, which is located at the front of the engine on the driver's side.
because you did it wrong
1 - 3 - 4 - 2
According to www.therangerstation.com , for the 2.8 L V6 engine : spark plug AWSF - 42 C spark plug gap .044 inch ignition timing 10 degrees BTDC firing order 1 - 4 - 2 - 5 - 3 - 6 distributor rotation CLOCKWISE
The spark plug firing order is ( 1 - 3 - 4 - 2 ) and the distributor rotor turns CLOCKWISE
From the front of the engine, the spark plugs are numbered 1-2-3-4. The firing order is 1-3-4-2. - Haynes Repair Manual #36071, 1993-2005 Ford Ranger Pickups.
the timing should be set top dead center with the number one spark plug
the ranger station . com ( no spaces ) Click on Technical Library
The firing order should be stamped onto the engine block at some location, or on the stickers at the front of the hood.
have u checked spark plug wires, ignition coils, timing,spark plugs or had it hooked to a reader?