91 MPV sputtering, then no start
 

I changed the oil on my van, and added some Marvel Mystery oil to the crankcase and fuel, as well as a bottle of upper cylinder lubricant. I then drove about 100 miles, and towards the end of the trip I would come to a stop, and when trying to accelerate after stopping, the engine would sputter down almost to stall and I'd have to give it quite a bit more gas than normal to get it up to speed. After shifting to second gear it responded normally. This morning I changed the spark plugs and afterwards it won't start. Cranks normally, but no turn-over. I'll be replacing the spark plug wires when they get in on thursday, and will be checking out my distributer rotor and points tomorrow morning. I was also thinking perhaps the fuel treatment could have dislodged a bunch of gunk and clogged my fuel filter. Can anyone tell me where this is located so I can check/replace it? Anything else you might know to check on please let me know. Thank you.

Zairian

1991 MPV 2wd, 4cyl engine.