I can only troubleshoot the components that we've produced and I've provided him all the steps necessary to do so. Once those are completed and if no fault is found in those he should investigate other systems that impact "boost".

Unfortunately the car is not outfitted with the necessary instrumentation to determine whether the turbo is actually creating air and it's being dumped or if it's not seeing the necessary exhaust pressure to spin the turbo.

That would require a turbo speed sensor and back pressure logging either in the manifold or in the turbine housing itself neither of which is supplied. So like everyone else in this thread I can only suggest broad troubleshooting steps to cover all the bases, which I've done and if the OP follows that steps he's likely to find and resolve his issue if it lies with the turbo itself.

Remember a turbo does not generate "boost" this is a misnomer it generates air the restriction that is your motor produces the "boost". So if the air is being dumped or not making it into the motor the turbo is not at fault and there's zero we can do to the turbo to correct this.


Now sparky I know I've upset you but let's keep it civil please.

Actually no it's not, while extremely rare the spring could have become damaged but not completely collapsed. What this would do is cut the spring pressure in half or worse let it completely flap open. The test I propose will completely rule it out being a WGA issue. While it's highly unlikely it's a valid test to confirm the operation of the WGA and move on to the next step.

If he truly wants to check the wastegate flapper door arm he needs to pull the turbo or at least the O2 Housing. Is that the easiest way to test it? No. But it's the right way and the safest way. Alternatively if the customer is sure the turbo is at fault I will be happy to pay for shipping back to me to personally inspect it free of charge.

Treat your turbo like you would treat your motor if you didn't know what your motor was revving to you wouldn't disable the rev limiter to test to see if it's revving high enough. Because that's what disabling your boost control system will do. What if the gauge is reading wrong and he's really seeing 20LB of boost and he disables the boost control system and the shaft speed spikes to 150,000RPM? What if there is huge air leak and the turbo is actually doing 54LB a minute worth of work? What happens when you can't tell how fast the turbo is spinning and you disable the ONE thing that can keep it from over speeding? Bad things that's what, unless you have a shaft speed sensor you should NEVER completely disable your boost control system, it's not a good idea.

-Michael

 

OK. Sorry, for the out of line commentary on my part. I will keep the growling and barking inside my kennel.

 

My suggestion about wiring the flapper shut was stated off the cuff by me without mentioning the potential risks involved in so doing. On turbo diesels we do this all the time but on an Evo a certain level of caution needs to be exercised when disabling the bypass.

I actually meant for him to just try it once(the OP seemed to understand the routine as expressedby him to me in a PM) and obviously the OP would have to keep his eye glued to the boost gauge and pull his foot immediately off the throttle once the neefle climbs past 10#. I just wanted to know if set up this way, the turbo will boost past 10#. He could pull his foot out of the throttle instantly, as soon as he sees an indicated 12-14 PSI. Surely, this wouldn't be totally reckless and at only 12-14# wouldn't be attaining excessive shaft speeds.

As Michael mentioned, the accuracy of the boost gauge should be verified first.

 

[QUOTE=Michael @ FP;10797400]..... The test I propose will completely rule it out being a WGA issue. While it's highly unlikely it's a valid test to confirm the operation of the WGA and move on to the next step...

The test you recomend is fine for testing actuator rod motion, diaphragm integrity and spring functionality. Overall, it gives you a rough idea as to whether the actuator functions at the manufacturer's advertised 18# rating.

The test however is far from comprehensive since it is performed while the engine is at rest. Therefore, it does not take into account the totality of the dynamic forces lifting the flapper valve, other than manifold boost pressure alone which only acts on the actuator spring/diaphragm assembly. Most notably, the test does not take into account exhaust gas energy, aka inlet pressure.

Inlet pressure, per se is the force which is causing the flapper to lift off its seat beforethe actuator's advertised 18# spring rating would indicate, thus allowing exhaust flow to bypass the turbine wheel prematurely. The test that you are suggesting is simply not relevant to the totality of the OP's issue. It is OK for testing springs in the lab, but is meaningless for testing the actuator in its working environment.

So, you are at best only partially correct, Michael. At least in this particular case that test won't yield any useful information. It does as you point out, verify spring/diaphragm functionality as well as actuator rod movement at equilibrium. It can demonstrate flapper valve cracking pressure and full open pressure but it only simulates manifold boost pressure acting on the diaphragm, right?

I call your test a static test. It is basically the same test run on an actuator on a bench with a Mighty-Vac, or a bicycle pump. Your test does not tell us at what PSI the actuator rod moves at when the car's motor is running and exhaust gases are flowing through the turbine housing. For the above reasons the flapper is lifting way earlier in real life than it does in your lab test.

Therefore, your test leaves out at least one important dynamic force: (exhaust)inlet pressure. Inlet pressure is a variable dynamic force acting directly on the face of the flapper valve. Your test does not take turbine inlet pressure into account. It only considers manifold boost pressure.

Turbine inlet pressure builds exponentially and at 20# it coexists with boost pressure at a 2:1 ratio. So, inlet pressure acts on the face of the flapper at a rate of 2 PSI for every 1 PSI of boost pressure.

In your test, only boost pressure overcomes spring pressure. But, in actuality, when the motor is running and exhaust is flowing through the turbine housing, inlet pressure is exerting a lifting force about double that which manifold boost pressure is exerting against the diaphragm.

The OP's low boost problem only manifests itself when the combustion process is producing exhaust gases. Due to the additional dynamic of inlet pressure when boost pressure is actually being generated, your static bench test is incoclusive, incomplete and irrelevant.

The OP needs to know why his flapper is lifting early when the turbo is producing boost dynamically. His scenario is therefore not totally represented by your isolated air source alone hitting the diaphragm while the engine is at rest and no exhaust pressure is acting upon the flapper valve.

 

So what is the fix?

 

Who the funk knows. Good question though.