boost drops to zero "0", nada

I've developed a problem that's kind of strange.



My truck builds boost normally, and holds steady boost at highways speeds. I've pressure tested the air-air and it holds 30psi easily. I've completely blocked off the wastegate, knowing that I would get an overboost and a defuel without a boost fooler.



However, when I stand on the injectors and spike the boost to 28#, it only holds for a few seconds and then drops like a rock to zero, noses over, smokes and spikes EGTs. It's like a boot completely popped off and I can hear it unspool.



I checked the pinwheel, I don't think there is any way for it to spin on the shaft. As far as I know, the turbine is part of the shaft. And lastly, there is very little oil passing the seals and no chewed up housing.



480,000 plus towing miles, I can't complain, but what is it?

 

Check air filter???

 

Would the MAP sensor be taking a dump??

Could it be your boxes??

 

Yeah, i've got a drop in with a modified air box and it's fine.

That's why I pulled the elbow out and stuck a pipe plug in, the wastegate is completely disabled at this point.

I haven't ran a box since I bought my X400 Stevo.



I don't think it's defueling because the EGT's go sky high and the exhaust gets thick gray.



It has to be dumping on the drive side somehow, but I'm serious, it goes from 24# to zero as fast as the needle moves.

 

If the WG is ruptured (the internal diaphragm), the pipe plug would do very little...

 

Well, that's what I was wondering, which is why I disabled the wastegate all together. I mean, it has to have cold side pressure to accurate, right? The diaphragm takes cold side pressure to actuate a rod that dumps on the drive pressure side or hot side, right?

So, since I disabled the WG, I should get an overboost and a defuel regardless if the WG diaphragm is in tact ... ... ... ..... what am i missing here?

I'll tear into it more tomorrow and I imagine it's a WG problem, but it drops like a rock ... ... ... ... ... I mean from 24# to zero faster than you can say "zero".

 

is the turbo stock? if so i can't see it being the turbo wastegate. the wastegate on mine is still on factory settings. it cracks at ±24psi. you can hear it in the exhaust. with smarty i can well over run the wastegate to 30psi.

the only time i have seen a reaction like that in an engine has been when i have had my 6. 5td and the egr stuck open. . the cummins has no egr so i am kinda confused why it is doing so. even with a hose or intercooler core leaking you will have low boost, not no boost and it shouldn't drop like that.

 

What I was getting at is that if the actuator is defective, it is only vacuum "controlled" from one side (or there would be two vacuum lines to the actuator)... this indicates to me it has a spring on the other side for the vacuum to pull against (or maybe nothing at all and depends on boost?).

If the diaphragm is bad, waste gate may be simply overcome by the boost and blown open... once it blows open (pops), it might not easily reset and it would probably be easily held open with nothing to pull it closed? Your sealing it with a pipe plug will do nothing if the diaphragm is already ruptured...

I'm still thinking its the actuator...

 

Yup Nick, factory original turbo.

I'm going to throw this on the wall and see if it sticks, lol

If the turbine side is wore out and clearances are maxed, could the drive pressure become too high to hold? I mean, could the drive pressure and compression equal out to simply stall the turbo?

I don't know, I'll have a new one in my hands tomorrow and know more then ... ..... stay tuned.

 

If clearances are worn, it would build to a point (max out) and hold it... just like any other pump. It would not drop like a stone to zero after reaching a max boost. If it will build 28psi initially, it should hold similar... if everything else is working.



My friend has a 97 Jetta TDI that did a very similar thing, it was the controller for the waste gate... the actual computer in his case, the turbo was fine. It would run great for all of 30 seconds then fall flat until restarted.

 

the wg actuator on the stock turbo is a simple spring seated pot. if the diaphragm was damaged, it would not actuate as the pressure reference would bleed through the diaphragm acting like a boost elbow. now if the housing and wg shaft is rusted, it might hang up and cause slow boost build but once boost is built and the wg is bleeding off exhaust pressure under load it would maintain 23-25psi where the factory wg setting is.

do you have an exhaust brake? if you do and for some reason that is actuating can cause the boost problem. you need a pressure drop across the turbine for it to spin. if the pressures equalize across it it kinda stalls [still spins but creates no boost]

if no exhaust brake, take a look under the truck and see if anything has damaged the exhaust or if something has plugged it. quick test if you have band clamps on your exhaust is to drop the mid pipe and go for a spin with only downpipe and see if it still acts up

is there any stored codes?

 

Jeff, do you have an exhaust brake? If you do, could it be activating inadvertently?

 

Our wastegates operate off of boost pressure. Our engines do not go into a true vacuum state. The boost presure overcomes the diaphram spring to move the gate open allowing exhaust to bypass turbine.

 

I would hook up a rail pressure gauge to see how the rail pressure is holding. You may be barking up the wrong tree just looking at boost if you already have verified the CAC system will hold 30psi

 

hmm... could be.



if rail press fell, that would really kill the fuel atomization out of the nozzles. . dribbling fuel won't combust well and will cause the engine to stumble [and cause egt and smoke issues]. maybe cp3 is sucking the fuel filter canister dry?.





from what i gather, he tested the CAC only. not the plumbing from the cac to the intake horn.





it is kinda hard to diagnose this sort of problem over the internet.

 

Well, as tempting a it is to let this thread die and not admit how stooopid I can be, I won't do that to you guys.



A while back I got into a terrible dust storm in the desert SW. I was in it most of the the day, and the northern AZ dust is like small black glass shards. My eyes were bleeding red, my interior was coated in this black dust etc.



Soon after, I started having cooling issues and replaced the thermostat and fan clutch. When that didn't work, I took a chance and hit the radiator with compressed air which caused a huge plume of black dust. So I soaked it down with engine cleaner and pressure washed it, problem solved.



Along the same time, I was certain that my blend door was broken again because I had no "fresh" air flow, but had good "recirc" air flow. I've had this HVAC worked on at least 4, maybe 5 times, so it was no surprise. However, I was surprised when they returned my truck saying the heater box was fine, but the fresh air intake was plugged up, problem solved.



Shortly after, my radiator developed a huge leak. Apparently the age and added heat separated the tank from the cores and a new radiator was installed.



You see where this is going right? So, with my filter minder at 35% or so, it never dawned on me. It sits at 25% after a fresh cleaning, and gets cleaned after it passes 50%. Why I never thought to check it after all of that, I don't know, but I didn't. At any rate, the filter was apparently so plugged with that dust that it was cauing enough of a vacuum to stall the pinwheel.



So that's my bonehead move of 2009, but I do have a new turbo now :-laf

 

doh... ... ... ... .

 

I know, I know, the guy who does my heavy work (clutches, injectors, etc) even said something about it. It was not one of my most shining moments