<img src="/forums/images/graemlins/shocked.gif" alt="" /> <img src="/forums/images/graemlins/shocked.gif" alt="" /> <img src="/forums/images/graemlins/shocked.gif" alt="" /> WHAT AM I HEARING???!!!!!

Way to go!!!! <img src="/forums/images/graemlins/kewl.gif" alt="" />

If it was my DD, I would probbally replace the defective part.

Never ordered from them, but the lower plenum goes for $237.74 on Mitsubishiparts.net.

Anybody ever ordered from this place before? I've got a list of stuff to order and I'm very tempted!

This is what I did and posted in May of 2003. Now have a total of 150k miles on it. I have a 95 SR with 139k miles. Rebushed the butterfly shaft when I was changing plugs and putting in the late model lifters. For the front bushing next to the vacuum operator I used a piece of brass tubing from a hobby shop to sleeve over the existing plastic. The back bushing I made from brass stock and turned down in a lathe. All the interior bushings were some sort of flexible rubber/ vinyl against the shaft itself and sleeved with hard plastic against the cast aluminum plenum. The plastic was cracked and partially gone in most of them. I bushed these with brass tubing again from the hobby shop and reused the flexible inner pieces. I lubricated the all with antiseize compound, Not really difficult, but time consuming.

[ May 02, 2003, 09:12 PM: Message edited by: 89raider ]

Bringing this back up, as I'm researching my next project.

There's a misstatement above. If the vacuum actuator for the two stage plenum on a 3.5 DOHC is disconnected, it allows the butterfly valve to remain open, allowing most of the intake air to use the shorter "high-speed" runners, meant for high RPM use. Engine vacuum closes the butterfly and makes the intake air travel through the longer runners, enhancing torque at sub-3000 RPM's.

If disabled by simply disconnecting the vacuum actuator, or if simply left in place in a worn state, unfiltered, unmetered air will enter the intake manifold at the point where the shaft that the butterfly valves attach to passes through the lower plenum to connect to the vacuum actuator linkage (which answers the last post above).

If the lower plenum is/is not disconnected, but left in place in a "worn bushings" state, the possibility of rattled-loose parts attached to the shaft, or parts of the bushings the shaft is mounted in, can come loose and be ingested through the intake.

In any case, the suitable repair is:

A) Remove the butterfly valves, shaft and bushings from the inside of the lower plenum and plug the hole where the shaft exits the plenum at the front. This disables the system and allows most of the intake air to travel the path of least resistance through the shorter, high-speed runners, although a little air will still probably travel through the low speed, long-length runners.

or

B) Replace the plenum with the updated part (cost as of Aug 2011 is around $420, shipped from Mitsubishiparts.net). You'll also need to spring for a bunch of gaskets.

or

C) Repair the old plenum by making/finding new bushings for the shaft to ride on. This involves trust in whoever/however the repairs are done. The more I think about this option, the more it makes me uneasy.

I think all three options mean you're going to have to take it all apart, even option A. And, if you go that far, you should be replacing the plugs and wires and testing the coils at least. Might be a good time to replace those evil heater hoses at the firewall, too, just to add to the list.

Mine was disabled by option A before I or Monte3 owned the truck, I believe. I am considering restoring it and have been given a used plenum by RyanY.

I think Ray (off-roader) replaced his recently. If that's the case, what are the impressions?

Anybody have any other ideas to add? I know this is old, but it's what came up when I searched.

John B.

Mine has a sound that appears to be like this. The guy I got it from says it's the water pump, but it doesn't leak a drop, or get hot. Guess something to add to the going thru cost. <img src="/forums/images/graemlins/scared.gif" alt="" />

i have a center section that has the butterflys removed and has been blocked if anybody need one

SRTNate did a writeup in one of his posts, he repaired his with mostly off the shelf parts found here locally. Look it up and give the repair a shot, I dont think it cost but a few bucks.
John

On both the Gen 2's I had I disabled it before it ever leaked, to avoid any problems in the future. Reconnected and disconnected several times and I didn't notice a difference.

FWIW, there was a guy on the old VMag board named Tim C who tried to fix the shaft by re-bushing it himself. It fell apart and he destroyed his engine.

i cold not tell the difference with and without other than no vac leak

Well it sounds like something to really (not) consider if, as it sounds, there's no discernable difference between having this system function or having it completely removed and disabled. I'll likely remove the whole plenum assembly when I replace my plugs, wires and coils, rather than take it apart to replace the lower plenum, then. Mine's safely taken care of.

Just to be clear, though, for those of you that have had the system both functional and not, there was no difference in low to middle torque? No difference in mileage?

John B.