So working on a 2005 F150 with a 5.4. Started off as a phaser replacement. Turn out the passenger side timing chain guide was badly damaged.

Front timing chain cover came off and replaced the guide and phaser. Got everything back together and it ran rough. Pulled the front timing cover off and the passenger side was off a tooth. Retimed that passenger side and also replaced the tensioner because the seal on the old tensioner wasn't the best. Now rotating the engine, i noticed the tensioner pushes then retracts. Seems like a vaccum is created pulling the plunger in, but not entirely sure. Only the passenger side does this, not the drivers side.

Worried about putting the front cover and valve covers on, buttoning everything together and having it skip another tooth because of slack in the chain. Anyone come across this? Any fix for it or reason why it does it?

 

The tensioner should not collapse even without oil pressure behind it. Normally if you buy new a tensioner it comes with a little clip to hold the piston down while you install it and the guide behind the chain so they definitely have a strong enough spring inside to hold the guide out while your cranking the motor over . Even mine that had 173K on them still had good spring pressure when I replaced them so it sounds like the spring in your tensioner is broken. I would just replace both the tensioner and guides while I had the front cover off just to be safe.

Also because the guide failed the chain was likely hitting the front cover shaving aluminum off. That ended up in your oil pan and will now be on all the rod and main bearings. Luckily the aluminum flakes are pretty soft so it will likely just embed itself into the bearings and wear smooth but it could have an impact on your oil pressure down the road or cause a catastrophic at some point. I would have thought the oil filter would have screened the aluminum and prevented it from getting to the bearings but at least on mine it did not. I'm not sure how it got to the bearings but it did.