Old boost Problem Resurfaced!

Long story but suffice to say i only had .8 bar of boost after full decat, tracked the problem down to a duff 2and turbo which was replaced along with its twin, after this i was in TTC mode and it made 1.2 bar, swapped it back and can only make just .8 bar again! back to TTC and still only .8 bar,

so I'm starting to think that there is maybe a problem with EGBV VSV after checking through the system the second turbo EGBV actuator has one feed from the pressure tank and the other to the VSV which i presumed was held closed via the pressure tank, by the ECU, until both the EGCV and the IAC valve where closed to achieve spool up, so baring this in mind i thought it may be that the EGBV VSV (or the ECU switch point) was giving trouble, so i bypassed the EGBV VSV but unfortunately it didn't help!

Now i'm looking at the problem in that if i have the system in TTC, i have now wired the IAC actuator and the EGCV open (i already checked that the pressure tank was holding pressure anyway) that the only thing that could stop boost being built was turbo 1 and 2 waste gates which the circuit i have described relates to, anyone have any more ideas, cos unless there is a problem with turbo no 1 VSV and waste gate, which i know there isn't, the system is just running in a twin parallel turbo mode relying on just the waste gates for boost control,.

got 300mls to do tomorrow

Update to this, if anyone has a good knowledge of the system? and would care to discuss then please PM me:)

I have just done a 600ml trip with the system in TTC mode, i had the just the vac hoses done but i have now wired the two applicable actuators, now i was still getting only .8 bar but on occasion i would get the boost up to 1.0 bar and then it would seem to drop back back to .8 bar! like it was being switched out, so i set about trying to track it down the problem, first i disconnected the EBV VSV with no result i then bypassed it, same result, next was to disconnect the no 1 turbo waste gate VSV no change, next was to try with both the VSVs disconnected, no change, so i then thought why not bypass the no 1 turbo waste gate VSV and suddenly i have over 1.2 bar! in fact it peaked at 1.4:( it also had a kind of jump as the boost built to just .9 bar so i wasn't very happy with that, so the next step was to also bypass the EBV VSV again, and this seems to work:d about 1.2 bar, so my conclusion is now that there is a problem with the no 1 turbo waste gate VSV and although tested, maybe there is a dogey signal from the ECU?

So now basically the system is now functioning as a parallel turbo setup relying on the two turbos own waste gate actuators as there is nothing else to get in the way.

Mate,

have a look the FAQ for Ian C's post on the sequential set-up here http://www.mkivsupra.net/vbb/showthread.php?t=35926

There is only one wastegate, on turbo 1. If the wastegate VSV is not working I would expect it to bleed air off from the actuator, thus raising boost. It should be open at low boost so the air just circulates back into the intake system.

Too complicated for me... Hope you get it sorted

J

so i then thought why not bypass the no 1 turbo waste gate VSV and suddenly i have over 1.2 bar! in fact it peaked at 1.4

When you say you bypassed the wastegate VSV do you mean you removed and blocked the hose coming from the wastegate actuator to it? Was this still in TTC?

The EGBV is redundant in TTC mode and does not act as a wastegate. When you say you wired the IACV and EGCV VSV's open was this electrically? To completely rule out the sequential setup (Pressure tank/VSV's/control valves) open the IACV and EGCV by connecting a foot pump to their actuators then wrap wire around the linkages to mechanically hold them open, then block off the hose supplying pressure to the pressure tank. See the bottom half of this page: http://www.mkiv.com/techarticles/ttc/ttc.htm If the car runs fine then there's something wrong with one of these components.

To check the wastegate itself, stick the foot pump on to one of the actuator connections and block the other one off. The wastegate should start to open with about 12psi and be fully open by 18psi. Check it shuts smoothly when the pressure is released.

If you suspect the wastegate VSV as the problem get a new one or an aftermarket EBC (which replaces it).

If none of the above works you're probably looking at a boost leak. Start by pressure checking the IC.

You could also try removing the boost source pipe to the wastegate actuator and blocking it off while in mechanical TTC (meaning the wastegate will never open). Take the car out for a drive and (very) carefully see what the boost does. It should massively overboost so if it doesn't then there's a boost leak or the turbos are duffed which you have already ruled out. My car only made 0.5 - 0.7 bar in this situation and eventually traced this to the BOV sticking open and dumping boost all the time.

I have already checked all the actuators and VSVs when i changed the turbos, but the way the system is behaving has got me a bit flummoxed,

thats why i have been thinking it may be down to VSV control from the ECU,

Yes i am now in mechanical TTC EGCV and IAC are wired open, so baring a boost leak (which it docent seem to behave like it has one going by past experience, and i have checked the BOV) so that leaves the waste gates and the VSVs controlling them, if you look at the diagrams you can see that one side of each actuator goes directly back into the intake side of the system, and the other goes to their own VSV which modulates boost by oscillating the normally closed gate, which in turn goes to the low pressure pre turbo side, so if these two VSVs are bypassed the actuators will stay closed and then the system relies on the restrictor ring to limit the boost,

I still had unstable and low boost until i bypassed both VSVs so i can only surmise that maybe the ECU responds to the MAP sensor input and modulates the VSVs, or that the response is preprogrammed, just theory the last part but kind of makes sense to me.

Did you ever get this figured out? I have a problem somewhere in the system, but don't know where yet. When I installed the second decat, my jspec was boosting to .9-1.0 bar (summer) for about a month, then it suddenly dropped, and now only boosts to .7 -.8 bar, even on really cool days. Power is noticebly lower than it was before at .9-1.0 bar. Sometimes, when the car is cold, and I first take off, if I give it a little, the car boosts, but then when I lift off mid rev range, it hesitates a little, like it isn't getting fuel or spark. I put new plugs and a new fuel filter in about 6 months ago but it was doing this before then. Any ideas?

Yes kind of, as I like TTC, i virtually eliminated all VSVs and actuators, except for the waste gate actuator, and now have a boost controller, don't have any problems with this set up:) next i will be fitting UK turbos, so i will loose the RR, and will probably rip out all the actuators and VSVs/pipework as well,

your problem sounds like it could be down to the pressure tank not holding pressure, have you checked?

No, I haven't, but am reading up on how to do it now. Sounds like it's a PITA and you have to do it from underneath. That accurate?

To check that the pressure tank is working, after you have been for a run using boost, pull off the hose that goes to the IACV VSV, you should hear the air escaping as you disconnect.