Guys,

Finally wrapped up my plenum plate install last weekend but I've been suffering a bit.

To summarize: New (hughes) plenum plate+gasket (yes, it was leaking), new intake gaskets, new passenger side head gasket (front/rear manifold bolts on that head seized, requiring both torch and machine work to correct), plugs, wires, distributor cap and rotor, thermostat (180 degree), exhaust manifold gasket, valve cover gasket....man the list seemed longer when I was buying it. (well, plus 4 ball joints, 2 tie rod ends, 2 calipers, 2 hoses....)


The problems (after I got the mixed up 6/8 plug wires sorted, and did the "proper" wire re-rerouting per the TSB):

Significant audible vacuum leaks after a heat/cool cycle. Sounded like a turbo spooling up off idle, until a manifold retorque. Still leaks bad at high vacuum (full throttle, high rev, drop throttle - sounds like a blow off valve!) and the off-idle whistling seems to be coming back after another 50 mile round trip to work.

The other problem is that once the truck warms up, at idle, it feels like it's misfiring on 1 or 2 cylinders. I haven't been able to track it down, and I dont know for sure it's spark or gas, or maybe just the vacuum leaks... After a bit of driving it will seem to happen on light/mid throttle up to about 1500 rpm. Idles -fairly- but not perfectly smooth when "cold" (summer, florida, ya know..)

When installing the intake manifold it took about ten trips around (after the 12 step process of getting there) at 12ft/lbs (per Hughes) to finally get it to settle down after installing it, and since then pretty much every time I apply torque wrench (so after a heat/cool cycle) it takes a few more to get it torqued to spec again. Of course, since the alt and a/c compressor have to come off to get to the front bolts, that's not exactly fun.


Is 12ft/lbs really right for these things? I assume it's that low for a reason, but damned if I can get it to stay. Should I pull the bolts and swap the antiseize (see above about stuck bolts.. ) for locktite? but with the temperature of the heads, I wouldn't expect locktite to help much - it would just melt.


Anyone have any ideas about either of the problems? Need to haul my tractor up to my moms place to help her out, but don't want to make the tow with it running like this.


For reference, it's a '00 5.9 (gas) 2500.


thanks!

...david

 

12ft pounds is right for the intake manifold bolts. Seeing you just went ahead and torque the bolts to 12 pounds. Acording to the FSM, First step is the torque them at 6ft pounds then recheck (following the sequence), then torquing them down to 12 ft pounds. Did you tighten the TB bolts? Also, did you put a bead of Black RTV sealant on the corner for the intake manifold?

 

mark the heads of the bolts with a line to determine whether the bolts are backing off, or whether the intake is settling in deeper. its sounds like its settling.

if the bolts are backing out, i'd remove each one one at a time and put rtv on the threads. it will make it stick, but coat the threads and prevent seizure.

whatever you do - do NOT overtorque the bolts. its aluminum....

 

Followed the multi-step process that Hughes suggests (it's out in the shop...) which starts with ~48 inch/lbs on the center ~4 bolts a few times around, then rolls up a few more inch pounds, then again, then ~6ft/lbs on all the way around, then finally 12 until they stay there.


Good idea on marking the heads, I'll give that a shot. (note that only the manifold is aluminum, and it's only under compression from the bolt - the head, or at least my heads, are iron. )

I retorqued the TB as well, even though I never pulled it off.

 

oh, and yes to a bead of RTV on all 4 corners, where the rubber center/oil seals meet the flat intake (air and water) seals.

I was able to tell where the leak was, at least last time before I retorqued, by spraying brake parts cleaner around the manifold - spraying along the side (head/manifold, where the intake runners go in) caused it to stumble at idle.

 

yes, heads are iron and solid as a rock, but the ears of the manifold are aluminum, and are suspended up in the air just enough to ........ snap. damn, i hate saying that.

 

check to make sure that you put back the vac hose for the MAP sensor.

Also,

Make sure that your airbox is on correctly. If that metal circle tab is not straight around and it is not sandwiching the airbox plastic with the TB lip, your airbox will leak. It will sound like a loud vac leak

 

this won't look pretty, and you don't want to do it until you're sure its settled all the way in - but a big, fat, solid bead of rtv along the seam will seal it up and avoid redoing it.

 

Which one is that? as far as I've seen I got them all back on (only 1 vacuum line on the TB, exits forward, loops around to the passenger fender. then the PCV > manifold (drivers side), brake booster, the the small hard line off the multi-T on the passengers side that goes many places, including a forward-running line that heads under the battery.


Yep, addressed that one too (amazing how noisy that is), replaced the now-in-four-pieces airbox to TB gasket, too.

 

did you reconnect the Passenger side vac line from the valvecover to the top of the airbox? That is the PCV fresh air side (pulls fresh, filtered air from the airbox).

Other than that i can't think of anything else. unless the rear gasket from the intake manifold shifted. i am talking about the little balck one with the dip in it that goes around the distributor divit in the block.

--Dan