c_akira

iTrader: (1)

Hey guys, I need some help diagnosing a second turbo boost problem. I’ve been doing a lot of searching but haven’t found specific answers to my questions. I’ve also been using the auto sport race tech site (ASRT Home Page) to troubleshoot but so far no luck.

Here’s the background: car was working fine with a perfect 10-8-10 boost pattern. Then one day I started losing boost. I would get 6 psi on the primary followed by a drop to 0 at 4500 rpm and an audible boost leak. I found a crack on the underside of the cross over pipe and replaced it with a new one. I’m now getting a solid 9 psi on the primary turbo up to 4500 rpm followed by a drop to 0 and I can still hear a boost leak from this point to redline. I inspected all the vacuum lines under the UIM and leading to each of the actuators as well as the 1” hoses to the CRV and BOV. Everything thing looked fine (note vacuum lines were all replaced about 18 months ago). I then connected a spare boost gauge to the nipple on the back half of the y-pipe (the side connected to the second turbo compressor) and went for a drive. I noticed that the second turbo is not producing boost at all (before or after 4500). I’m still getting 9 psi at the manifold from the primary until 4500 rpm, at which point manifold pressure drops to 0.

Here come the questions:

1. Am I supposed to see any boost from the secondary before 4500 rpm? I know the CRV is venting while the secondary is pre-spooling but should I see even a little bit of boost when my gauge is connected directly to the compressor? I’m thinking of running the test again but with the CRV closed (by disconnecting the vacuum line) to see if the second turbo generates any boost before 4500 rpm.

2. I suspect that the pre control actuator is not opening to allow the second turbo to pre spool. But even if this was the case wouldn’t the second turbo come on line when the turbo control opens? Or are the turbo control and pre control linked in such a way that the turbo control won’t open unless the pre control is also open?

3. Since the second turbo is not producing any pressure that means that the Charge Control Valve is not opening at 4500 rpm (i.e. as the CCA needs boost pressure from the second turbo to equal the pressure from the primary before it can open). So then why am I seeing a sudden drop to 0 at 4500 rpm? What’s happening to the boost provided by the primary turbo if the CCV is closed? I would expect it to drop gradually rather then suddenly. Is it being vented by the WGA as it’s “blind” to the lack of pressure from the second turbo?

Sorry for the long post. Any thoughts would be greatly appreciated.

c_akira

iTrader: (1)

A quick update: I decided not test the second turbo pre spool with the CRV closed because I didn't want to surge the compressor. Instead I decided to just do the test again. Interestingly I got different results this time. Maybe there was a problem with the T adaptor I used last time. Anyways, I can now see that the second turbo is generating boost. There is no boost during pre spool (as expected - all boost is being vented) then a quick jump up to 11 psi at 4500. However, what's more interesting is that the higher up the rev range I go the higher the boost builds on the second turbo compressor. It got as high as 15 psi at 6500 before let off the throttle. I repeated the test several times to ensure I got consistent results - which I did.

I then hooked up the boost gauge to the line going from the UIM to the Charge Control Actuator. From looking at the vacuum line diagram, this line should be providing vacuum to the CCA before 4500 rpm (to keep the CCV closed) and then switch to pressure from the second turbo after 4500 (to open the CCV). The test showed that I was getting vacuum from idle which slowly climbed to 0 pressure at 4500 and stayed there.

I think that this is telling me the following:

1. The CCA is not getting boost from the second turbo which means that the Charge Control Valve is not opening at the 4500 rpm transition point.

2. As a result, the excess boost from the second turbo is not flowing into the y-pipe and therefore not being vented by the BOV. This would explain why my second turbo continues to generate excess boost beyond 4500 rpm.

My next step is to take a closer look at the Charge Control Solenoid to see if it's malfunctioning.

I would still appreciate any thoughts!

c_akira

iTrader: (1)

Ok, so I'm just posting this final update in case it might help someone else out in the future. The problem is now resolved. As suspected, it had to do with the CCA not getting pressure from the second turbo meaning that the CCV would not open. I replaced the Charge Control Solenoid as well as the vacuum lines into it and the vacuum line from the second turbo compressor to the UIM. Things are now back to normal.

Can't believe no one offered any thoughts. This forum has certainly changed.

neil_jdmr

I found the same for seq twin issues tbh