Sticky Wastegate?
 

Lately, in the last week or so, I've been noticing heavy black smoke and a general lack of boost.
While driving casually, nothing registers on my gauge. good gauge, good line.
When I accelerate moderately, it peaks at 5PSI.
Let the car cool overnight, and I have normal boost and no black smoke.
Drive up a fairly steep hill, tranny kicks down, and the onece normal boost reading of 15PSI at that RPM continues to build till about 20PSI then drops off to normal levels rather abrubtly. Once I get my RPM back down in 4th gear, the next moderate accelleration is heavy smoke and no boost.

Sticky wastegate. because the lack of boost also varies. one instance it'll peak at 5 others it'll peak at around 8 or 10. It's almost as though the valve stem is hanging up in it's bore or something.

how does one go about unsticking a stick wastegate? take apart and clean?

15-20psi is going to kill the engine, I'd look into the turbo and electronic overboost solenoid to make sure everything is ok. 20psi is rod-bending territory. :eek:

Well, these high pressures aren't for any more than a half a second on HARD, infrequent and rare acceleration

I have no functioning OB protection. other than the wastegate itself...and no ALDA..

I just want to know if anytthing can be done to the wastegate to make it operate smoother than it is now.

Yeah, it's a sticky WG valve, I can watch my boost gauge build up to the point that the WG should open, it passes to like 15 PSI then instead of leveling off at around 10 it drops to zero as though I'd taken my foot off the throttle, without actually doing so.

Check your wastegate hose. Sounds like you have a leak.

Replaced that yesterday.:)

Anyone care to explain to this newb how the turbo/wastegate/overboost function together. :D

Anyone care to explain to this newb how the turbo/wastegate/overboost function together.

BTW, the newb I'm referring to is me. :D

Turbo creats boost pressure which begins opening the wastegate at a set pressure. Wastegate allows some exhaust to bypass turbine and exit the tailpipe with out spooling the turbo...equilibrium is reached. If something interferes with the wastegate's opperation and the boost gets too high (over 15 psi or so) the overboost sensor cuts off the turbo's pressure signal to the injection pump, which then limits fuel (and power).

Excellent, thank you for the help.

Does this mean that the overboost is just for protection and is not used the vast majority of the time?

Also, how does the turbo send the signal to the IP, is that vacuum, electric, or other?

And... is the wastegate setpoint determined by a spring?

Correct, the overboost is strictly for protection if the wastegate were to stick closed. In reality, I'd venture to say that most of the systems won't work properly due to the sensor on the manifold getting plugged with carbon over time. I recently tested the SD without a wastegate hose. The circuit never worked.

The "banjo fitting" which you've probably heard of, is attached to the back of the intake manifold. It sends a pressure signal to the "ALDA" which allows the IP to advance the rack and provide more fuel to the cylinders.

The wastegate setpoint is a crude spring affair that is not calibrated very accurately on most vehicles. Some are set to 6-7 psi and some are close to the specification of 12-13 psi.

Thanks Brian, now I know why I cleaned the banjo fitting and adjusted the ALDA! :idea3:

So if the wastegate opens at 6psi then the car would be underpowered correct?

I'll have to take some pictures to see if I can correctly identify these parts now. :D

Yes, if the wastegate only allows 6psi, the vehicle won't produce full hp.

That'll be the ticket.;)

Exactly what mine seems to be doing. I get 9 psi with the wastegate hose off. :rolleyes: :( I should check for exhaust leaks nefore I pull the dang turbo again I guess. If it comes off It is getting replaced with some sort of upgrade...holset! :D

Something is amiss or the wastegate is leaking badly. You should get about 20 psi with the wastegate hose removed.