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740 TD04 Compressor Bypass Valve (CBV)

D

davewatson

New member
Joined
Jun 24, 2016
Location
Canberra, Australia
Hi all,

First post on the forum - from Australia; have a 90' 740 Turbo with the TD04. Only just taken ownership; my old man had it over a decade ago; rebuilt the engine and gave it to my sister when she got her licence. Its since been absolutely trashed - slowly cleaning it up as a daily to my fully setup Pajero. (running costs are less than half). The 740 is also running LPG to keep costs right down.

Problem I'm having - I've found the CBV has a massive vacuum leak - this solves my rough idle etc. I haven't been able to find any of the correct model online to replace it with. I also haven't found any decent information regarding blanking it (as to whether it needs just a flat blanking plate; or something molded to make sure that its in the right position). Alternatively is it something that can be repaired / modified & repaired? I have seen a bunch of rebuild kits (again none that appear to suit this model?)

Any advice / help is greatly appreciated!

Watson.
 
You can buy a replacement diaphragm from kinugawa. You could also try eBay, Td04 bypass.

You can also try searching for part number 271640 to see if you can find a local dealer.
 
Sorry for my ignorance. I have pulled the unit out of the car, and cannot see anyway to actually replace the diaphragm - where I would expect to replace it is crimped over.

MMTskFWsBJDR7yD56


Link to photo of unit (can't tell if embedded images working from my phone.)
https://goo.gl/photos/MMTskFWsBJDR7yD56
 
Can't see the pic, work proxy blocked it.

There are 2 styles of CBV's. The early style is a piston style, has orings that seal it to the housing. Usually they are pretty solid units.
The later style is the 15g style, with a diaphragm and metal cover that bolt onto the housing.

IPD and a few others have replacement diaphragms for them, or you can get a replacement unit from Forge that is serviceable, works a little better, but it's a good bit more money to do.

From your description alone, it sounds as though you may have the early style. Not much to be serviced there other than the orings.
 
Thanks - that explains why I haven't been able to find much information - wasn't aware there were different styles.

Is there anywhere that sells aftermarket replacements of the piston style? Unfortunately am lacking of wreckers that have 740's in Canberra.
 
wasn't aware that they shared the same turbo. Unfortunately either of those isn't sold domestically in Aus (only grey imports) - so are rare to see (the pt cruiser less so - I don't think I've ever seen a dodge neon); let alone scrapped.

What are my options for bypassing it and using an external BOV as an alternative? (It really is a massive vacuum leak).

If I remove the unit; can I use just a blanking plate; or does it need to be modified internally so that it doesn't act as if its permanently in bypass?

Thanks all for the help.
 
You will definitely need to bypass it internally, otherwise you'll have some issues building boost. Been ages since I've had one of those CBV's out but I think if you had a solid plug with an oring on it attached to a plate that would bolt onto the existing holes, you should be fine.
 
Any chance you can find a 94-95 turbo 850? If so, get the TD04HL-15G off and replace your turbo with it. Needs a reclock and a wastegate bracket made, but it's pretty easy.
 
Unfortunately a replacement diaphram won't help since I can't dismantle the unit without decent modification (and I may aswell have a bypass 'plug' machined up for that effort).

gsellstr sounds like you've hit the nail on the head - exactly what I had thought was going to have to happen - Shouldn't be too hard to machine up!

ONE last question regarding this. As it currently is probably minimally operational; and is causing me a massive vacuum leak (which is causing havoc on everything else); what are the consequences of bypassing it temporarily? As I understand it; it will struggle to boost (which isn't a massive problem since I also need to find time to replace the clutch - and have been babying it everywhere anyway). Is it going to cause any other problems that I haven't realised?
 
Sorry to resurrect a dead thread, but this is the exact issue I have going on (how my CBV is the old piston style and I cannot service/replace the diaphragm). Before I ask more, do you think my diaphragm is even bad? (In my case, idle is fine)


I did a vacuum test and have a big leak at the CBV (smoke comes out). Also, I have "alot" of flutter after I build boost and let off the throttle. Is my Diaphragm bad? I cannot open the CBV to inspect.

If CBV diaphragm is bad , please need help understand what to do next. So far I understand I would need to block off that part of the turbo (with a plate or somehow modifying the current CBV (I dont understand that part, as described in thread) .....and install a BOV? (but then I was reading that a BOV can wreck havok on the fuel injection system/MAF sensor)

Please help dumb it down for me to help conceptualize
 
There are three types of cbv options on a 90. Sure it's a mitsu and not a Garrett t25?

If so there are still two types for the early mitsu.
 
ZVOLV said:
There are three types of cbv options on a 90. Sure it's a mitsu and not a Garrett t25?

If so there are still two types for the early mitsu.
Click to expand...

Yes, I have the same one as poster above. It does not look serviceable.

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Would a CBV from a different , newer turbo be able to be transplanted as a replacement? I am doing everything I can to not have the replace the turbo at this time, as my td04-13c blows well and builds boost, however I am being told the smoke test should not leak at the CBV. I was also thinking about having a machinist cut the top part off enabling me to replace the diaphragm and then weld back on but that is more of a pipe dream at this time
 
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