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hi guys/girls...i don't have a T4/T5 but I've noticed some of you guys are very tecky and maybe able to shine some light on a problem I have with my Mitsubishi L200. Its a 2.5 litre 4 cylinder diesel turbocharged by a variable vane ( or nozzle ) turbo. The truck every so often,particularly on long uphills towing a trailer, a EML comes on to say its overboosting. The EML codes are easy to read. I have a vacuum guage and it is indeed overboosting.Max boost should be 1 atmosphere 14psi with the occasional overboost allowed of say 18psi for five seconds.Ive seen 18psi regularly. The variable turbo is controlled by vanes as you know,which is why its called variable. Ive had the turbo apart, there is no axial or radial play in the bearings, and uses very little oil...maybe 1/2 litre in 5000 miles.The vanes are clear of carcon build up and the actuating ring that changes the angle of the vanes rotates/slides nicely It otherwise runs very well. There is a vacuum operated actuater that moves the vanes to control the boost. It also moves freely.
There are two limit screws that limit the angle of the vanes in their extremeties. One screw limits the vanes as they move towards the centre of the turbine, the other limit screw limits the vanes at the other end of the travel circumferentially if that makes sense. Where do I go from here to limit the boost?
Sorry this is very tecky i know....
Ive chatted to some guys on the L200 forum with limited success.....Can anyone share a few shouts...Regards Sibol




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hi guys/girls...i don't have a T4/T5 but I've noticed some of you guys are very tecky and maybe able to shine some light on a problem I have with my Mitsubishi L200. Its a 2.5 litre 4 cylinder diesel turbocharged by a variable vane ( or nozzle ) turbo. The truck every so often,particularly on long uphills towing a trailer, a EML comes on to say its overboosting. The EML codes are easy to read. I have a vacuum guage and it is indeed overboosting.Max boost should be 1 atmosphere 14psi with the occasional overboost allowed of say 18psi for five seconds.Ive seen 18psi regularly. The variable turbo is controlled by vanes as you know,which is why its called variable. Ive had the turbo apart, there is no axial or radial play in the bearings, and uses very little oil...maybe 1/2 litre in 5000 miles.The vanes are clear of carcon build up and the actuating ring that changes the angle of the vanes rotates/slides nicely It otherwise runs very well. There is a vacuum operated actuater that moves the vanes to control the boost. It also moves freely.
There are two limit screws that limit the angle of the vanes in their extremeties. One screw limits the vanes as they move towards the centre of the turbine, the other limit screw limits the vanes at the other end of the travel circumferentially if that makes sense. Where do I go from here to limit the boost?
Sorry this is very tecky i know....
Ive chatted to some guys on the L200 forum with limited success.....Can anyone share a few shouts...Regards Sibol




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Stop showing off. variable bloody vanes. ;) Mind you the German T4 150bhp has a variable vane too.
I think you said it yourself, you can limit the vane throw out at full chat. Think of it as a bike derailleur, they have a limiter screw at the top & bottom of travel. Not sure about your motor but if it's doable you just need to figure out which one to adjust.
 

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Thanks for your thoughts!! I would have thought the MAP sensor is the same as the boost sensor. I replaced the boost sensor with a mitzy original ( not cheap) as I like you thought it might be that. Ebay ones are ****.
The mitzy technical bulletin dated 2005 has this as a known . They say to adjust the limit screw so that the vanes can move more axially (radially). This has the effect of"reducing the turbo speed/boost pressure"...this I can understand...however all the very knowledgeable guys feel its the opposite limit screw to adjust. They say the other screw should be turned so the vanes cannot be moved so circumferentially (less flat). Does this make sense ! Ta for the thoughts ...Sibol
 

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Discussion Starter #6
Thanks Bingley for this..Ive enclosed the tech bulletin from mitzy. Id be interested to hear your interpretation of their advice about limiting the boost and opposed to the article you've found..they seem to contradict each other..Sibol
 

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You can tell that was written by an engineer & not a mechanic. o_O
To me I'd check the bottom bolt was touching its cam. If it isn't adjust the length of the actuator rod so it is. Then wind in the maximum travel bolt half a turn & see how you go. keep winding it in half a turn until the problem stops.
As long as you count your half turns you can always put it back if needed. To be honest it's probably the most over complicated Heath Robinson factory set-up I've seen since the Austin Mini. :LOL:I presume the set-up was about balancing the turbines like the spring of a watch for the return pressure to be correct.
Sell it & buy a T4 mate. 🤣 then you'll know what trouble is.
 
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