It may be the downpipe clamp.
This is where the first exhaust pipe clamps to the turbo.
Take the engine cover o9ff the van and inspect everything.
It only takes a pin-hole to make a problem.
if the clamp is loose all you will need to do is tighten it up.
And go to Lowes or Home Depot and buy a carbon Monoxide Detector
and velcro it to the inside of your van in the middle area. I have one in my van and it works great.
Mine never goes off because I don't have any leaks, but it works great and could save your life. You can pass-out while driving even with the windows down. Nothing to mess with..