neilp9876 Posted April 4, 2011 Share Posted April 4, 2011 Occassionally when cold the car would stutter a bit if I tried to use boost, fine once warmed up. I also noted a couple of times where the boost seemed to oscillate on and off when accelerating but could never get it to do it consistently. On the way home tonight I stuck the manu button on for no real reason, and the boost started to oscillate between 0.8 and 1.1 until it got to around 4 or 5k revs when it would suddenly relax and sit at 1.2 which is normal. Took the manu button off and it was fine again. Tried it a few times and it seemed consistent. Whats going on? I cant imagine it being directly related to the auto box, maybe it doesnt like pulling from low revs (ie. no kick down). But I cant help thinking there might be another problem, maybe a leaky vacuum pipe or something somewhere? Quote Link to comment Share on other sites More sharing options...
Wez Posted April 4, 2011 Share Posted April 4, 2011 Are you sure your not hovering the revs around the sequential change over rpm range from say 3000 to 4000rpm? Quote Link to comment Share on other sites More sharing options...
neilp9876 Posted April 5, 2011 Author Share Posted April 5, 2011 Are you sure your not hovering the revs around the sequential change over rpm range from say 3000 to 4000rpm? Having thought about it, I think it probably is doing something like that. Does lead on to another issue though, last time it was dyno'd there was a noticeable drop in power when it transitioned across the turbos. The drop was higher than it should be but the garage was uncertain of the cause. It could be that the oscillation comes from it trying to transition but loses so much power it reverts back to the first turbo, and so on. The question is then - what causes such a big drop of power on the transition, or is there a way of making the transition smoother. It uses an AVCR boost controller at the moment, could that be the cause? Quote Link to comment Share on other sites More sharing options...
mellonman Posted April 5, 2011 Share Posted April 5, 2011 check the vac hoses, and look here http://www.mkivsupra.net/vbb/showthread.php?35926-The-sequential-system Quote Link to comment Share on other sites More sharing options...
neilp9876 Posted April 5, 2011 Author Share Posted April 5, 2011 Not going to pretend I understand how the turbos work. However i do know the AVCR actually replaces the EGBV valve (I dont have one fitted anymore), so could it be that the controller isnt allowing the 2nd turbo to prespool properly? Quote Link to comment Share on other sites More sharing options...
neilp9876 Posted April 5, 2011 Author Share Posted April 5, 2011 Having just read this article about fitting a boost controller Ive realised it describes my setup exactly and also describes the symptoms I have where the #2 turbo isnt being pre-spooled properly. http://www.max-boost.co.uk/max-boost/supra/boosting_the_beast.htm Has anyone got any experience of this or made the changes described in the article, not something I would want to do myself but if it makes the turbos smoother then I will happily get it done. Quote Link to comment Share on other sites More sharing options...
neilp9876 Posted May 6, 2011 Author Share Posted May 6, 2011 Just to finish this thread off. I got hold of an EGBV valve and plumbed it in last night (The original had been removed when the boost controller was fitted), the trip to work this morning was a revelation, the turbos are so much smoother when they transition from #1 to #2. So not only are the turbos likely to be less stressed the power delivery is much better and it doesnt oscillate now when it brings the second turbo online. I guess I get less boost on #1 but I would rather have the smooth delivery. Thanks for the help and the documents, they were very useful. Quote Link to comment Share on other sites More sharing options...
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