930 wastegate function and how to check it?
 

i read in a previos thread that if the waste gate is not working properly it will break the piston rings. well tearing my motor down i found broken rings among a spun rod bearing. how can i check my waste gate if it is working properly? also would you suggest running an aftermarket spring to boost it to 1bar? will this harm my engine at all?

There's a lot of grey area with answering a question like that unfortunately. If the wastegate was working properly AND you were experiencing more boost then normal then yes, that damage is most likely caused by the wastegate. If it was failing and stuck open then the only effect of it is a loss of power because of lower than normal boost levels. To check if it's working properly you'd need to pressurize it with air pressure and make sure it opens fully within resonable pressures.
Now to your second questions, if your running pump fuel and no other provisions are made to handle more boost then it's a gamble as to whether your engine will handle the 1bar. Typically things like bigger (and more efficient) intercoolers aren't a bad idea if you want more boost, along with fuel enrichment devices.
I think that about sums it up.

cool thanks for the info. my boost gage was reading 1 bar at idle so i take it the waste gate is stuck closed?

Are you talking about the boost gauge under the speedo? ...if so, if it reads 1bar at idle, then I'm guessing it's unplugged or not functioning properly. Sensor is connected into intercooler, is orange thing about 2.5" tall, about 1.5" dia, and orange cover is rubber type mat'l. there's one wire connected to it.

if wg was stuck closed i'm guess'n you would have blown up car.

remember you're reading boost into throttle body. at idle you're going to have any boost, matter of fact it will be a slight vacuum.

What he said, and to add to it, if the 930 factory boost gauge is like the one in the 944 turbo, then is reads 2 bar total and it's value indicates total atmosphere not corrected to sealevel. So 1 bar would mean open throttle, anything above 1 bar is boost. If the 930 is corrected, then it's telling you have 1 bar of boost at idle which even with a stuck wastegate is impossible.

Factory boost gauge in my 930 read from 0 to 1 bar. It wasn't 944-style absolute pressure gauge. It's fed by electric transducer.

First of all, you should have checked maximum boost on your engine before problems happened. OEM gauge is not accurate. Use graded pressure gauge. An unmolested 930 boosts between 0.6 and 0.8 bar.

If wastegate fails, there is overboost protection switch that cut's fuel pump Vcc around 1.2 bar. It will give you "dash in your face"-syndrome when boost goes trough roof. Unfortunately, it's often bypassed by "harder boost spring"-vandals as it gets tripped sometimes in cold weather (1 boost springs are inexact and so are overboost switches. If your switch trips at 1.1 bar and you happened to have slightly harder spring and weather is cold, you might hit it)

If overboost switch is bypassed and wastegate membrane rupture occurs, you run high posibility of doing terminal damage to your motor (beyond broken rings).

It's unfortunately quite common to expirience broken rings even w/o going beyond 1.2 bar. It only takes bad gasoline, 1-bar boost spring, warm weather and heavy foot. Car will usually run even with broken rings but it will use lot's of oil and have bad leakdown numbers.


Testing the wastegate:

There are two inputs. One on the top is only a vent. One in the bottom is pressure signal. If you try to blow air trough top vent, you shouldn't hear any air escaping. If air is escaping, your membrane is ruptured and needs replacement. If you "blew" your wastegate from the top and it seams OK, you can try to pressurize bottom half of bell. You will hear some air escaping trough valve stem, it's common. Do not use more than 1.5 bar or you will blow the membrane. When pressurized, valve should move upwards from valve seat. Check valve seat for cracks.

If everything is OK, I recomend removing 1 bar spring and re-installing 0.7 bar OEM spring. 1-bar spring is a rude way of adjusting the boost, usually done by "mechanical" people solely beacuse they understand how it works but not much more. Once installed, 1-bar spring won't allow you to play with the boost. It will keep it at 1 bar (or more, depending on size of the turbo and exhaust system).

Better way of solving adjustable boost requirement is by using OEM spring and having 0.7 bar as "base boost". More boost is then attained by lowering the pressure in singal hose, either by mechanical (Dawe's device etc.) or electrical means (electronic boost controller etc.)

This will allow you to adjust boost from safe level upwards.

Spring-people will sometimes defend their choice by saying harder spring is better beacuse it reduces "boost creep". Boost creep is when wategate starts opening a little before boost target is attained. In reality (which is clearly audible when running open wastegate pipe), this problem is minimal and occurs on both spring hardness levels. It's inherently connected to analog way spring tension and membrane force interact and resolved by using electronic boost controller, which keeps wastegate de-pressurized untill target boost is achieved. There are even more intricate ways of controlling wastegate for minimal boost creep ( by applying boost on both sides) but it's out of scopes for this post.

Hint: be careful if opening the wastegate as there is lot's of energy stored in the spring. Use safety-straps.


Hope it helps.

Lots of good info, Goran!

Or you can use a couple of C-clamps. The newer version with rubber facing work better.

yes, mine has the 0-1 bar type (ie: not absolute pressure) and that is what I was describing.