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Discussion Starter · #1 ·
I have everything running in seq mode right now, I don't want to do TTC (TTC = single lag with no top end :)). The first turbo spools late. For example, 40mph in 4th gear when I hit the gas it hits about 3psi and slowly creeps.
What could be there problem here? I don't see any broken hoses, and no leaks. I was wondering if it was possible for the vsv to go bad and cause this problem, or is the first turbo independent from the whole system? At one point I was in 5th gear and hit gas and the turbo spooled right up and you could feel the car moving hard, was very happy about it, but than it started spooling late again.


Discussion Starter · #5 · (Edited)
David_rg79 said:
does that psi rise with rpms?
If so your wategate is stuck open
Yup, it only hits the boost when I'm at like 3K RPMS and up. The WG one on the first turbo, how can I fix it? Also is that directly installed on the turbo? Or is it the big can on the side of the turbos. Also, when I pulled one of the hoses off of the VSV air came out and than when I put the line back on the turbo spooled faster, and tha it was slow again :( Thanks for your help.

Discussion Starter · #7 ·
dzeiler said:
you posted this same question on mkiv mailing list and got many excellent suggestions I would follow that advise....

THis is what Lance said.

Is there low boost no matter what or is the #1 just late spooling? If it's no matter what, it could be the wastegate, otherwise see below:

1. I would want to check the IACV butterfly valve to be sure it is fully closing, I'd also be checking the IACV VSV. There is a little black "filter" on the outlet that seems to be important to IACV function (I remember years ago Guilly posted about a car with mystery issues and replacing the little black filter resolved them, strange, but true).

2. The reed valve block in the IACV control housing could be broken allowing boost from #1 to blow back through the #2 turbo before #2 comes online.

3. For the #1 turbo I would also be checking to be sure the EBV control is working correctly. If the EBV is stuck open, boost from #1 will be low because the OEM system uses the EBV in a wastegate like fashion to control boost from the #1 turbo. If the EBV were stuck open, there would be no boost control for #1 in the same way as if the wastegate were stuck open. In the same vein, if the EBV VSV were not working and stuck closed, boost from
#1 would be low, this could be caused by the wiring from the harness being accidentally shorted while the single turbo set up was installed. This would lead to an ECM failure in the sequential control components, but not complete ECM failure, and either a new ECM or a repair to the SMD
transistor(s) would be needed.

4. The actuators themselves. They need to be tested for leaks, diaphragm failures are not unheard of, and damaged valves like the EGCV are also known issues.

5. Pressure tank issues, or lines to and from the pressure tank could be damaged, cracked, kinked, missing, etc.

Is this enough to get you started?

'93 TT 6 speed Coupe
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