Does anyone have an idea as to why my van is having trouble starting?

insufficient Amperage and voltage the job done...tin/antimony alloy batteries [no lead no more] only lasts five years before it cannot charge back up easily...not to mention a compromised Amperage and insufficient re-charge times~ Clean the 1/0 cable from battery to the chassis...the lug end and the place where it bolts to~

...will SLO-roast the alternator as it tries to recharge a battery that ain't takin' a charge anymore~

the health of the ECU and the critical decisions are compromised as varying voltages and amperages are presented for normal operation...tosses out a CEL because the source of power is "iffy"~

...so clean the system ground [point 0-0 on your electrical schematic] the w/p or work point from which ALL electrical devices get their grounding....from dis-similar metals...actually "welding" the connection in place and creating corrosion with each use~

...finally let's look at the basics...air/fuel/spark/timing/valve timing----the orchestration of these things should be examined for proper operation...you could start by putting the key to the "on" position and listen for the fuel pump whirring and circulation through the fuel rail~

if it is a 300 6 cyclinder or eqivilent replace distributor pick up coil in bottom is bad fairly common on ford and old dodges