Shane Posted September 14, 2015 Share Posted September 14, 2015 My car has developed a strange sequential problem. 95% of the time you wouldn’t notice theres a problem. So you are cruising along around 70-80 and gently put your foot down and it drops down to 3rd and the boost builds normally on No1 up to 0.7 bar and then No.2 comes on line as normal, this is great and how’s its always been. However if drive a bit harder at this speed and get it to kickdown to 2nd there is hardly any boost (maybe 0.3-04 bar) until it finally gets into 3rd and whoosh its off again and drives normally. It doesn’t always do this, but it is getting worse and happening more often and only when you drive hard and it kicks down all the way. I have read through the guide and I suppose the closest scenario to it would be the description of what happens when the iacv VSV sticks/fails. Checked all the hoses and if I put a pump on the pressure hose to the iacv actuator everything seems to be free and moving with ease. Any suggestions? I don’t see the point of putting it into ttc mode as obviously from the times it works correctly, both turbos are producing boost and enough of it. Thanks. Quote Link to comment Share on other sites More sharing options...
mellonman Posted September 14, 2015 Share Posted September 14, 2015 Read the FaQ selection on the sequential system dude , IIRC its a sticking egbv Quote Link to comment Share on other sites More sharing options...
Shane Posted September 14, 2015 Author Share Posted September 14, 2015 Read the FaQ selection on the sequential system dude , IIRC its a sticking egbv Yeah I did read that but to be honest nothing really seemed to match the symptoms. But will take a more in depth look. Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted September 14, 2015 Share Posted September 14, 2015 Could be all sorts of things, but I'd probably suspect a vac hose due to the inconsistency. Also, they really need to be warm when you pressure test them. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted September 14, 2015 Share Posted September 14, 2015 If you have a controllable source of pressurised air at say 20 PSI you can pressurise the sequential control system and look / listen for leaks. You should also *REMOVE* every relevant VSV and test it with a 12V source and a Mityvac. A Mityvac should be on MKIV owners to buy lists long before anything else, unless you farm out maintenance to garagistes, they are not that expensive. Pressure tets and electro / pneumatic tests of the VSV's reveal the cause nine times out of ten. Quote Link to comment Share on other sites More sharing options...
Shane Posted September 14, 2015 Author Share Posted September 14, 2015 If you have a controllable source of pressurised air at say 20 PSI you can pressurise the sequential control system and look / listen for leaks. You should also *REMOVE* every relevant VSV and test it with a 12V source and a Mityvac. A Mityvac should be on MKIV owners to buy lists long before anything else, unless you farm out maintenance to garagistes, they are not that expensive. Pressure tets and electro / pneumatic tests of the VSV's reveal the cause nine times out of ten. Thanks Chris, I did have a very quick play using a bike pump to test the actuator on the iacv and its related mech was ok and sort of guessed I was going to have to test the VSV's next. I do have a controlled air source so will start with those and check the hoses as I go along. I was hoping someone was going to say something along the lines of " I had that last week and it was this this and this", not because I am lazy, but because time is always at a premium these days. Worse thing is that its intermittent of course so faults with components may not show. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted September 14, 2015 Share Posted September 14, 2015 If you pull off one of the two short s shaped hoses that go to the pressure side of the turbos, near the BOV one is connected to the pressure side of the sequential stuff, and applying pressurised air there in reasonable volume pressurises all the "stuff" and lets you look for weepy hoses. The slightly S shaped hoses go to two steel pipes. I can't recall which one, but looking at it will reveal which is right. Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted September 14, 2015 Share Posted September 14, 2015 It would be good if someone with a thorough understanding of the sequential system did a diagnosis 'how to' Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted September 14, 2015 Share Posted September 14, 2015 That's like asking a Barclay's employee to do a how to on fixing the Libor Can't have the great unwashed understanding it old boy, sorry If in doubt replace *everything* with new OE bits , or bring it here and magic will happen! Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted September 14, 2015 Share Posted September 14, 2015 I guess that someone will be me then! Once I'm clued up. Quote Link to comment Share on other sites More sharing options...
alxns7 Posted September 15, 2015 Share Posted September 15, 2015 Here is a great article I used, extracts from the TSRM with tips. Quote Link to comment Share on other sites More sharing options...
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