Hello. I have a Chevy cargo van with a 6.5L. Will only start if its plugged in. It has good fuel pressure. Glow plugs have juice. Maybe a bad ground somewhere?

 

You would get best answers posting in 6.5 section I believe, anyway I suspect the glows themselves are bad, only way to know is to remove them with pliers hold glow plug, touch spade lug to + terminal on batt, and have a heavy gauge wire to - term of batt and other end wrapped around the body.

Plug should glow to red tip to center in about 4 sec, if just a little red or no red then plug is bad.

For replacement get Bosh Duraterms or AC-60gs, 11gs or autolite 1110s or ok but don't last as long, DO NOT BUY 9gs if you find them those are obsolete and swell when they go bad.

How is your cranking speed?