How much vacuum is the 5.9 suppose to make at idle? My truck loses vacuum under moderate acceleration and at 55 going up a slight grade the cruise control can't hold the speed. I just repaired the plenum and timing chain with an aluminum plate and Cloyes double roller. I checked for vacuum leaks, there is none. Put a guage on the manifold and I make 18 inhg at idle. The truck seems to sightly struggle up hills. No oil on the plate yet, but it's only been a very hundred miles. Any opinions or suggestions?

 

Do you have the wild vent issue? There are two check valves one right next to the intake and another up where the vac reservoir is. It's possible the one next to the intake is bad or the vac line going to the cruse control actuator is craked. This is a major know area where they crack and leak. You will get the highest vac reading when the throttle is closed.

 

When I was working on the 4x4 actuator, I was seeing about 17.5 inches of vac. Not sure where they tap that on the engine. But there is a reference point for you. What is your idle rpm?

 

yes but only a little after the vacuum drops. I even have the updated check valve
About 500-650 can't really tell exactly but there's according to my scan tool. 17.5 I'm not getting that

 

Checked the intake with the throttle body off no oil in there that I can see but I'm wondering if I tightened the manifold bolts tight enough

 

Why do you think its a vacuum problem, not quite following the logic...

 

Disable ALL vacuum accessories. Pull the hoses, plug the ports. (except for one for your gauge.) See what manifold vacuum looks like that way.

 

I did that, got 17.5 exactly. Is that what it's supposed to make?

 

Hhhh...... I think spec is 18-20... So, you are at least close. Probably wouldn't hurt to re-torque the intake bolts.

 

I didn't use a torque wrench as you need an extension (which messes with torque) and want doing the math as my mind is still on the brakes.