What Is This ?? Plenum (manifold) buttrefly Issue.

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WeeMagna
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Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

What Is This ?? Plenum (manifold) buttrefly Issue.

Post by WeeMagna » 17 Aug 2017, 17:57

Hi everyone,

Thanks in advance :)

I am hoping someone might be able to tell me what this is...The round gold coloured thing.

See attached.

It is making a loud hissing noise. It looks like an EGR but I am not sure. Is it supposed to make a hissing noise?

Thanks.
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close2.JPG
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Last edited by WeeMagna on 20 Aug 2017, 15:32, edited 5 times in total.

WeeMagna
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Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 17 Aug 2017, 18:01

Oh, apparently I cannot post photos...

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Dougal
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Re: What Is This ??

Post by Dougal » 17 Aug 2017, 20:26

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WeeMagna
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Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 18 Aug 2017, 09:14

Thanks Dougal. I will try that.

WytWun
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Re: What Is This ??

Post by WytWun » 18 Aug 2017, 23:34

WeeMagna wrote:The round gold coloured thing.
Hmm... I'm not terribly familiar with what looks like a DOHC 6G74 (Pajero?) intake, but suspect that is the vacuum actuator for the inlet manifold long/short runner butterfly valves.
WeeMagna wrote:It is making a loud hissing noise. It looks like an EGR but I am not sure. Is it supposed to make a hissing noise?
I doubt that it should be making a loud hissing noise - that would suggest a vacuum leak of some sort.

WeeMagna
Member
Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 19 Aug 2017, 09:22

Thanks for the reply.

It sure is a DOHC (also known as a quad cam) 3.5.

It has been making the hissing noise all the time I have had the car. It is just that I only hear it with the bonnet open. I decided to make a serious effort to find the hissing and tracked down to this thing...

It has a wire like rod that comes out the base. If I press a finger on the rod the hissing reduces. It has an inspection hole and with the engine OFF I see a white plastic disc of sorts. But with the engine running the white disc cannot be seen. It has a single vacuum hose as per photos.

If I spray it with silicone spay the engine revs change by about 100rpm (up or down at random) and the hissing stops but for less than one second...Not game to try WD40 as that can damage some types of air seals.

There are no other issues with the engine.

WeeMagna
Member
Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 19 Aug 2017, 14:40

Well...A little research finds that this thing is in fact the vacuum actuator for the butterfly assembly in the plenum...Thanks WytWun, you are the man :D

There is an issue thou...Apparently a fault in the actuator can cause vibration of the butterfly which cause the screws to come loose. Screw then drops through the plenum and it's bye, bye engine !!

Many, many years ago I had a sierra (Suzuki) that got written off by a loose screw...I have seen the damage a screw can do !!

On another forum they say just remove the butterflies...even if there is no problem. They say the butterflies are only there to give an extra 5 hp at low revs. What ??? If I live to be 150 years old I am never going to be pushing any car so hard that I need an extra 5 horses...it's got about 220 already and 2 sets of low range gears with 4wd !!! What is 220 ponies going to do that 215 cannot ??

So I figure I will just remove the butterflies. I have no idea if the actuator is faulty or not. Maybe this hissing noise is normal but maybe it is not.

I value the opinion of members here over that of other forums. Is there any reason (other than a 5 hp drop in power) why I should not remove the butterflies ?

Cheers

WytWun
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Re: What Is This ??

Post by WytWun » 20 Aug 2017, 00:44

My vague understanding of the DOHC butterfly operation is that at low engine revs the butterfly position is set so that air flows through the long runners (the manifold loops out to the right in your first photo) to the lower manifold. Above a set RPM, the butterfly position is switched so that airflow goes directly to the lower manifold. I don't know what the RPM threshold for the switch is but expect it to be somewhere in the 3000-4000rpm range.

To test some theories, you might try disconnecting the butterfly control solenoid wiring. Without the butterfly control available I would expect the butterflies to be in the long runner position and you would probably notice that the engine performs well below the switching threshold but poorly above it, as the long runners apparently impede high rev performance quite noticeably. If you used a coil spring or some similar means to hold the butterfly shaft in the short runner position, performance (particularly torque) may be reduced at low revs but good at high revs. Removing the butterflies completely could be expected to produce about the same results as holding the butterflies in the short runner position.

I've not investigated the construction of that sort of actuator but they're quite commonly used (e.g. throttle actuator for cruise control in 3rd gen Magna). I suspect that there's a rubber diaphragm with the actuator rod attached via plates. If the hissing reduces when you pull the rod out of the housing, that would suggest a leak in the diaphragm which is being reduced in size as the rod extends. It might also be that the leak is in the butterfly shaft seals (from vibration) and changing the butterfly shaft position changes the leak rate.

If the vacuum line is directly connected to the intake manifold (rather than a vacuum pump like the Magna CC) it may be introducing enough air to lean out the mixture (especially at idle which has strong vacuum) which then has to be compensated for by the oxygen sensor. If you have access to a logging rig, checking the long term fuel trims might show the effects of this.

If you have the intake manifold modified to remove the butterflies (and I gather this is a common mod to these manifolds for the reasons you mention), you will also need to disable the solenoid that controls the vacuum supply to the actuator - or remove the line and solenoid and block off the vacuum source completely - to restore vacuum integrity.

WeeMagna
Member
Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 20 Aug 2017, 11:54

Thanks for taking the time to reply :)

Yes, apparently it is a very common mod, according to what I am reading.

It seems that the 5hp I was reading about is only a theory. In practice it is almost impossible to measure any difference. Apparently they used these butterflies for a short time during the 1990's but found the practical application did not match the theory, so they stopped using them.

The threshold is 3000 rpm. In a lighter car like a Magna the difference is noticeable but only just. But the Pajero weighs a bit over 2 ton. Even if the extra theoretical 5hp was achieved, in a 2 ton car under 3000 rpm it will not be noticeable. On top of that, the 5hp theory is only possible in absolute ideal conditions. In reality it would be more like 1 or 2 hp.

I am not going to investigate this hissing noise any further. I will just remove the whole butterfly system.

Thanks again for your reply.

WeeMagna
Member
Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ??

Post by WeeMagna » 20 Aug 2017, 12:35

Just a quick up date for those that might be interested.

I thought I would take a look and I found this...
rod.JPG
rod.JPG (116.68 KiB) Viewed 3631 times
This is exactly what has been described as the cause of vibration which then causes the screws to come loose. The plastic sleeve on the rod is completely gone and you can see how bad the ware groove is. Not the best of photos, but you can see just how big it has made the hole.

Those butterflies are definitely coming out this week !!

WeeMagna
Member
Posts: 56
Joined: 13 Aug 2012, 15:10
State: New South Wales
Model: 1995 Pajero
Engine: 3.5-Litre 6G74 V6 24V DOHC
Transmission: 4 Speed Straight-Shift Automatic

Re: What Is This ?? Plenum (manifold) buttrefly Issue.

Post by WeeMagna » 31 Aug 2017, 12:30

An up date for those interested and those with the same problem.

I removed the entire butterfly one week ago... Absolutely NO noticeable difference in power !!

The pic shows the butterfly fully open. As you can see fully open is only about 5mm. In other words the long run is used all the time. The butterfly simply does not open far enough to use the short run. Fully open at least 90% of the air still goes through the long run. With the butterfly removed, most (if not all) air will now go via the short run. So in theory there will now be a difference...but in practice logic wins.

It is fuel injected. So it does not matter how turbulent the air is (which is the theory of the long run), the air fuel mixes after the air is pulled into the chamber. It is pulled or sucked in with a great deal of force so it will make no difference how turbulent the air is at entry. Coupled with the fact that the Pajero is a big heavy car, designed, geared and powered for big heavy loads and towing...you could put a turbo charger on it and not notice any difference !!

The problems found --- The hissing was in fact the butterfly shaft the the vacuum valve attached to. It has a plastic sleeve which had worn away and caused ware of the hole in the plenum. The gap between the shaft and the plenum was about 1mm. The fix -- simply a bolt with washers large enough to cover the hole and a nylex lock nut.

On the butterfly, all the screws were there. But 4 of them had come loose but were held firmly (but not tight) by carbon build up. The fix of course was remove the entire butterfly assembly.

Conclusion... Remove the butterfly, even if you don't have issues at the moment, remove the butterfly !! If you are using a catch can, remove the butterfly ASAP !! If you have a catch can then you simply will not have carbon build up to hold any loose screws.
Bfly.JPG
Bfly.JPG (139.27 KiB) Viewed 3598 times

z80
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Re: What Is This ?? Plenum (manifold) buttrefly Issue.

Post by z80 » 05 Sep 2017, 10:15

Good work finding that mate....will save someone's engine ...
Twin turbo Mitsubishi 380GT -16 PSI boost with 3.9 litres and LSD conservatively at ... 270Kw @ 710Nm at the wheels!
Supercharged TMR380 ....complete with custom Quaife limited slip differential.........191kw @400NM at the wheels
No virtual dyno here.

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