My van backfires under acceleration

Replace spark plugs and spark plug wires using OEM quality parts... 'Possible' intermittent ignition coil failure but not as suspect as plugs & wires.

Could also be a clogged up catalytic convertor. A Shop could perform a back pressure test to determine this but could be a possible issue.

both of these shops posted very viable causes of your problem however is the check engine light on, we would really need to see the van and run diag on a scan tool