In 6G74 removing intake manifold butterfly valve completely.

[Gaurav]

Hi Everyone, new member here saying big hello to all. Need some experienced member help please.

I drive 1999 pajero 6G74 DOHC engine, which is experiencing very mild missing from sometime. I changed to platinum spark plugs, new coil, and still the missing is there. Its on further investigation we found out that the butterfly mechanism on the top intake manifold is having a slight play and air leak. Play is exactly on the yellow round bush on the top as shown on the picture

According to my mechanic, we can freely cancel this mechanism as it is irreparable. Mechanic is advising to install one side closed bolt in place of yellow bush, and remove all the butterfly valves from all the 6 holes below.

Please advise if anyone has done this before or if there is an alternative fix to cure this slight air leak causing the missing.

[Silvertune]

Edit, removed

[Gaurav]

Thanks Silvertune, for reply. Much appreciate it.

Mechanic removed the butterfly yesterday and missing got cured. So far no difference felt in driving, acceleration, racing etc. Will comment on the fuel mileage as tank finishes.

Do you know what exactly the function of these butterfly valve? My mechanic said one butterfly is all any car need in throttle body and he also don't know why Mitsubishi gave 6 flaps in each cylinder...!

Appreciate if someone can shed some light on this. Mitsubishi here in Dubai selling whole intake (bunch of banana) assembly and don't offer spare bushes for flaps. Changing the new one is only alternate for me or source any used one. If i source used one which would probably be the same age as mine will have same issue???? I mean to ask these bushes wearing and creating a play is more of aging wear & tear or it was just my bad luck and no one else has experience this same?

[Gaurav]

Here is the picture guys for reference. Thanks for all elp and suggestion. Cheers.

[Silvertune]

The butterflies are a part of what is called a dual geometry intake manifold. It works with flow characteristics of air. When the butterflies are closed the air is sucked into the motor through a longer set of runners. Longer runners promote air velocity and torque for low RPM operation. When the engine reaches higher RPMs the butterflies open and let the engine breath through short fat runners that can supply larger amounts of air as the engine sweeps out a larger volume. This promotes power.

The truth is variable geometry manifolds are a thing of the 90's, they aren't really used anymore. The reason is because they're quite ineffective in most applications as you've found out by the lack of performance change. On this particular platform the VGT manifolds are mostly used in gutted form (butterflies removed) because it promotes more power and since we have big V6's we don't need the extra low end grunt (if there were any to be had).

The ineffectiveness of the manifold is why your Montero runs fine now. It is not a "high performance" engine per se and so the characteristics the changing manifold provide are not extrapolated enough to make a noticeable difference particularly not when numbed down by engine wear. So long as you have no vacuum leaks out of the manifold itself there shouldn't be any issues in the end.

[Gaurav]

Silvertune: What a great way to explain to newbie, totally impressed with your knowledge, patience and your helpful nature. You are a true asset to this club.

As per the manifold leak, mechanic tested thrice and there is no leak and truck has no missing now. Instead i am experiencing much free throttle response now (after reading your explanation, i understood why). Which makes it run great.

Referring to low end torque, i like to ask that i drive this truck quite often in sand in extremely hot weather, where lo end torque is quite instrumental in climbing steep dunes and towing sand-bogged cars. Will that be of any concern now as its always running on long set of runners???

So bottom line if fuel efficiency stays same, i don't need to get new one?

[Silvertune]

Since you deleted the butterflies you'll always be running the short, power runners. That said, if you're not noticing any difference in driveability you won't have any issues doing what you've always done with it before. The only reason I can't tell you for sure if you've lost torque is because no one has dynoed a dual geometry manifold with the butterflies shut versus open but chances are the differences are pretty negligible.

[TurtleTamer]

When I set up my GTS manifold to run with them open all the time I noticed a slight drop in low-end torque but it wasn't much of a difference. Sure it runs better with it all working properly in this engine, but the butterflies are also still in there so I can't speak for any difference if gutted. I can say the car didn't have any problems, just didn't run as well up to 4,000 rpm when they would normally open.

To the OP: do you work at the Sunset Safari? I thought they only used Toyotas but I haven't been there since 2010. It was a blast!

[Gaurav]

Thanks again Silvertune for honest heads up. I will keep noticing the torque on my next offroad drive and also the fuel mileage variation (if any).

TurtleTamer: Thanks for sharing your experience and knowledge. So far i haven't notice any issue with 4k rev, full throttle downshift touching at 5k was fast as before. Will check my 0-100 tomorrow to see if its still around 8.5-9 secs or not.

Safari companies here in Dubai uses toyota as they are cheap work horses, they cant afford other cars in hi maintenance business. Btw we are the guys who offroad for fun and adventure, as most beautiful part of country lies in an offroad span (Mountains, Sand dunes, water cross valleys).

Here in UAE very less people take Mitsubishi offroad as they are not very capable (newer model) against Nissan, Jeep, Land Rover and Toyota's. My Pajero being old model (better ground clearance and offroad stance) with 3.5l engine on SWB makes it real capable offroad. And that's why im saving this rare capable truck to my last possible effort.