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The mkiv Supra Owners Club

intermittent boost problem doing my head in


Chris and Alana
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I have had this problem for a while but the supra hasn’t been driven much with the bad weather so I forgot about it. I took it up to Scotland on the weekend 180mile trip each way and on the way there it all seemed fine boosting 1.15bar but on the way back it would only make 0.75bar according to my EBC. It done this for about 100 miles. Every time I floored it would act the same. Now accelerating from 2.5k revs it gets approx 10psi boost and I can feel the change over at 3.5-4k revs as usual with a slightly louder exhaust note but the boost doesn’t change more than 10psi. I then thought I must have a boost leak but after approx 100miles all of a sudden I floor it and I then regain all my power 1.15bar. Once it started working again it never battered an eye lid and worked correctly all the way home.

 

Like I said I have had this problem for a while just forgot about it and it does the same thing randomly. I checked the intercooler hosing and all seemed fine. I have checked the vsv's and all (3 of them) seem fine. (I don’t use the wastegate vsv as my EBC takes over the job). I put pressure down the actuators I can get to and they seem fine as well. What could cause this intermittent boost issue? It has me baffled and it is quite annoying.

 

This all happens with the EBC off. I didn’t bother turning it on as there is no need in the colder weather.

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Thanks for the links :)

 

Right the only vsv I had an irregular reading across when testing them was the IACV vsv. It read resistance in the mega ohms rather than 42 ohms or what ever it should be but it still opened with 12v across it. I can hear the change over of the turbos so Im guessing that the EGBV is openeing but sometimes the IACV actuator isnt openeing fully, not allowing No2 turbo to come fully online. Does that make sense?

 

The only thing I hope it's not is the EGBV actuator as you cant get the bugger :(

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Hi Hadyn, It cant be a difference in outside temps as it can work (produce 1.15bar) and not work (0.75bar) all in the same journey. Plus the power difference is quite norticable.

 

I have also just tried TTC mode by by-passing the IACV vsv and the EBCV vsv. I took it for a drive and it worked fine (well for TTC mode anyway) First time I tried this mod and I kinda liked it, sounds much more gruntier lower down the rev range. Anyway, I floored it a couple of times and I got 1.1ish bar straight away every time. Obviously there was no boost until 3.5k but apart from that it all worked spot on.

 

What have I just proved is working? Pressure tank, all vacume pipework, all Actuators and un-by-passed vsv's? Plus both turbo's :)

 

If this mod proves my EGBV actuator is working then I think I may dare say it could be an intermittant fault with the IACV vsv, as I know the actuator works from TTC mode.

 

Any tech minded people feel free to slap me if Im wrong (but also :help: me)

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I have exactly the same issue at the moment....very annoying. I get 0.5bar when I kick down sometimes and sometimes get the full 1.1bar.

 

A group buy on all 4 brand new vsv's would be a nice easter present for lots of people I think as well as an overhaul of the vacuum lines that make up the sequential system. Both I am considering doing very soon and think both will be money well spent imo

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I have exactly the same issue at the moment....very annoying. I get 0.5bar when I kick down sometimes and sometimes get the full 1.1bar.

 

A group buy on all 4 brand new vsv's would be a nice easter present for lots of people I think as well as an overhaul of the vacuum lines that make up the sequential system. Both I am considering doing very soon and think both will be money well spent imo

 

I have already changed most of the vacuum lines (just not the ones I cant get to) but all new vsv's would be good :) I love the supra but at the same time it is such a b**ch when things go wrong. It doesnt even have to go wrong in a really bad way either. Infact if something would just brake it would be easier to trace and repair than something that decides it doesnt want to work now and again.

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Well looks like it's fixed :nana: John (hodge) the kind fella let me come down to his place on sunday and try a replacement IACV vsv. Once fitted I took it for a run and it worked spot on. It then operated perfect on the 20-30min drive home and fine again today. Anyway, I'm over the moon and another boost issue sorted. Thanks again john :thumbs:

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Well looks like it's fixed :nana: John (hodge) the kind fella let me come down to his place on sunday and try a replacement IACV vsv. Once fitted I took it for a run and it worked spot on. It then operated perfect on the 20-30min drive home and fine again today. Anyway, I'm over the moon and another boost issue sorted. Thanks again john :thumbs:

 

Nice one mate :) I think I will try and pick one up over the summer as well as our symptoms sounded almost identical

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