In (IIRC) Mid-Late 99 they switched over to the returnless setup. My late 99 has the returnless setup.

If its returnless, the FSVT pump will work. If not, I don't think it will.

I beleive the FSVT pump puts out like 255LPH and the stock pump is 155LPH.

1999 Mystique LS V6 Alpine CDA-9807, Rear deck sub, Opt. TB, K&N RU-3530/MAF adaptor, custom heatshield, FSVT 17's, SCT 4-program chip, Eibach's/ST200's, Hella Fogs...