* Wheelbase: Different wheelbases resulted in different weights.
* Engine: A larger engine adds weight.
* Options: Power options, additional features, and even the type of interior trim all contribute to the overall weight.
* Cargo: The weight of anything in the van is added to the curb weight.
Therefore, there's no single definitive answer. You won't find a precise weight without knowing the specific configuration of the van. To get a close estimate, you'd need to find the original window sticker (if it exists) or consult a 1991 Ford Econoline E150 brochure that lists specifications for different models.
You can expect the curb weight (weight of the van without cargo or passengers) to be somewhere in the range of 3500 to 4500 pounds, but this is a broad estimate. To find a more precise figure, you'll need to do some additional research based on the specifics of the van in question.
