The 1992 GMC Typhoon came equipped with a set of cloth/leather embroidered seats (loved by some, hated by many) that just so happened to have a manual lumbar support bladder that you pumped up with a hand bulb and and deflated with a 1 way valve. While not the most advanced system, it does get the job done on long distance drives by adding a bit of comfort to one's lower back. The 91 GMC Syclone shares the same lumbar system. This article can be a guide for fixing a Syclone's lumbar system, however some steps may differ slightly.
HOWTUNE ARTICLE: REPLACING THE LUMBAR SUPPORT HOSE, 92 TYPHOON
HOWTUNE ARTICLE: REPLACING THE LUMBAR SUPPORT HOSE, 92 TYPHOON