When you undress the front of the engine, look closely at the crank pulley bolt to see if it's loose. If it is, look closer to see if the pulley has spun as a result of a broken woodruff key. If so, check further to see if the crank sproket has also spun.

If the trouble isn't with the crank sprocket, I'd carefully check the tensioner and tensioner spring as Sparken suggested.

It seems impossible to have a running engine one minute and virtually no compression the next without a complete catastrophic engine failure or a slipped cam belt.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum