I have a 1991 Peterbilt 377 with a 60 series Detroit that won't start at all. It started out starting sometimes but when it did it had a gray smoke and sounded out of time but would smooth out after a second or two and ran great going down the road, to now it won't start at all. It has a little bit of smoke coming out of the stacks but won't fire. any and all help would be greatly appreciated.