Van backfires and shakes

I recently replace the left hand cylinder head on my 99 grand caravan 3.3l, because it had a broken bolt on head. Now it backfires and shakes when you are driving down the road already replace cam sensor,plugs, and did compression on engine no compression on all cylinders how in the world is this thing running please help maybe it needs computer programming out of ideas.

All your questions can be answered by a quick trip down to your local independent mechanic. If all cylinders have no compression then it’s a miracle if it runs.

Clearly your valves are not timed correctly…and your ignition might be out of phase. Normally, your piston would push spent gasses out, the exhaust valve would close, the intake valve would open (there’ll be a bit of overlap), the fuel will be compressed, and the spark plug will fire. In your case, I think the vaporized gas is being expelled, the exhaust valve is closing, the intake valve is beginning to open and the injector starting to spray, and the spark plug is firing! With the intake valve opening!

You need to go back and confirm your valve timing AND confirm that the spark timing isn’t out of phase.

You’re right…how in the world is this thing running?