4packet Posted March 27, 2012 Share Posted March 27, 2012 Has anyone got any experience of this to save me dismantling excessive amounts of the car? Essentially the issue is restricted to anything below 4000rpm. If the revs are already above 4000rpm with no boost, then I can go WOT and both turbos make good boost. If I start at low revs I will typically see normal boost for a period and then it starts dropping off and will not make the change over to the 2nd turbo. Sometimes this occurs around 3000-3500rpm, but once properly warm it seems to happen at much lower revs and will soetimes give no boost at all. The boost sounds different too, almost like a groan. I suspected that the 1st turbo boost pressure was leaking out the 2nd turbo, but can't figure out the failure mode. The IACV actuator moves freely and is sprung closed (I believe) and the electrical actuator clicks fine on the bench. There is a bypass circuit illustrated in the schematic, could this be the issue. Seems easy on the schematic, but to pull it apart doesn't look like a 5min job. Is there is a seal that can deteriorate? Thanks in advance Martin Quote Link to comment Share on other sites More sharing options...
Nic Posted March 27, 2012 Share Posted March 27, 2012 http://www.mkivsupra.net/vbb/showthread.php?27904-Sequential-turbo-problems&highlight=sequential http://www.mkivsupra.net/vbb/showthread.php?35926-The-sequential-system&highlight=sequential http://www.mkivsupra.net/vbb/showthread.php?35924-Sequential-turbo-hoses&highlight=sequential Quote Link to comment Share on other sites More sharing options...
4packet Posted March 28, 2012 Author Share Posted March 28, 2012 It's a great resource, which I've referred to many times. It doesn't describe the symptoms I'm experiencing or elaborate on the below. IACV When it isn't switched, there is a small flap in the IACV assembly that allows any boost generated by #2 turbo as it prespools to join the intake stream, preventing turbo stall. Is this a robust flap or could it fail and allow reverse flow? I'm assuming it functions as a one way valve. Is there a way of checking it or dismantling it without removing the entire casting? Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 30, 2012 Share Posted March 30, 2012 Perhaps your EGBV is stuck open? Or is being opened as boost from #1 builds, due to a stuck VSV? This would bleed exhaust gas from turbo #1 as boost pressure rose, but as soon as the second turbo switched in it'd recover. Quote Link to comment Share on other sites More sharing options...
4packet Posted March 30, 2012 Author Share Posted March 30, 2012 I will have another look at the EGBV, but as you say if everything else was OK, it should switch to both turbos as normal. It has never switched to both turbos once it has lost boost on #1 turbo. Quote Link to comment Share on other sites More sharing options...
bignum Posted March 30, 2012 Share Posted March 30, 2012 Have you tried ttc mod to see what boost you get then? Quote Link to comment Share on other sites More sharing options...
4packet Posted March 30, 2012 Author Share Posted March 30, 2012 Tried that years ago when my IACV wasn't working. Not done it this time as it makes good boost off both turbos. Have to be off boost above 4000rpm before going WOT to get the full effect. Normally I'd just settle down with it and pull it all apart, but I'm already up to my eye balls trying to squeeze that V8 into the RX7. Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 30, 2012 Share Posted March 30, 2012 It has never switched to both turbos once it has lost boost on #1 turbo. Ah I missed that bit. That'll be the exhaust gas control valve not opening then. You might have an intermittent leak in the pressure system that runs this valve, which would bleed off the boost from #1 turbo and then when the IACV opens it vents what's left backwards out of turbo #2. Turbo #2 can't spin as the EGCV hasn't opened to let it flow gas. -Ian Quote Link to comment Share on other sites More sharing options...
4packet Posted April 3, 2012 Author Share Posted April 3, 2012 I had a look at the EGCV pressure circuit and it seems OK. I'm inclined to think that this part of the system is OK as both turbos come on line if you are already above 4000rpm (change down into a low gear and give it a couple of seconds off the throttle). It just won't switch over if you start accelerating below 4000rpm and the boost has already started to drop off. Quote Link to comment Share on other sites More sharing options...
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