31inch tires fit 91 wrangler no lift?

No, 31-inch tires generally will not fit a 91 Jeep Wrangler without a lift. Even with trimming, they'll likely rub on the fenders, control arms, and possibly the body. You might be able to squeeze them on with some serious modification, but it's not recommended as it will severely limit articulation and potentially damage components. A lift kit is necessary to accommodate tires that size.