Stix37867

iTrader: (1)

I suspect that I’ve been having some turbo issues for quite a while now and it's getting bad enough that I may be able to actually diagnose it now.

I virtually can't control my psi output anymore except for stock wastegate spring pressure (7psi). I normally have psi set to 13-15psi and can't come close to hitting it anymore including tapering off over time. I usually will hit maybe 12psi and can watch it flutter and drop to almost 9psi. After checking the usual culprits (check valves, solenoids, flapper doors), I got fed up and plugged the hose going to the wastegate (pulled and plugged hose from the turbo manifold not solenoid). I went for a test run knowing that my boost should shoot up and almost not stop so I was ready to shut down once it did. Well I recorded the run on the gauges and I still MAYBE hit 13psi and then watched the boost taper off.

After this I reinstalled the wastegate hose and started to test the boost at different sources. I installed the boost gauge line to the y-pipe both before the secondary turbo butterfly and after. Both seem to function normally and the sequential system appears to work as it should. The butterfly opens when it should and do not see any pressure when it is closed. Also, the boost pressure readings from the y-pipe are around 15psi or so and do not really taper off much if at all. I do not know how much pressure drop I am supposed to see after the intercooler but somehow am not getting the after throttle body boost pressures I want.

Now what really has me baffled is that my boost controller (Knightsports EBS III) gets its pressure reading from the upper intake manifold. Logic tells me that if I set the controller to 1.00 PA (Pascal) and boost only registers at lets say .78, then the controller should not open the wastegate till that pressure is reached. This logic is verified by my experiment with removing the pressure source from the wastegate.

So in the end, something is regulating boost without needing to bleed off exhaust pressure. The only thing I can think of that can do this is the butterflies in the throttle body by not opening completely thereby restricting the amount of pressure the motor sees. I still have a couple of things to check out on the throttle body but everything appears to be operating normally on the throttle.

Some additional info that may be helpful...
Installed two different sets of turbos both with their own wastegate actuators.
Boost controller does work fine, I can set boost to stock 7psi or even a pound or two higher with normal results.


Can anyone chime in on what I may be missing or overlooking?

DaleClark

iTrader: (55)

Haven't seen any mention of boost leak testing. That's the #1 culprit in boost problems. If you're venting boost, there's your problem.

If you unplugged the wastegate and still didn't get much boost, that's the only way I can see that happening.

Dale

Stix37867

iTrader: (1)

Building a pressure test system tomorrow just to verify that I don't have any leaks. I have never heard any major leaks and haven't seen anything obvious during quick inspections but I suppose it's a possibility I missed something. I'll update once I have some results.

Stix37867

iTrader: (1)

Of course it had to be something simple. Even worse is that I've touched this piece at least 3 times over the summer while either changing the turbos or looking for other issues and never caught it.