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Discussion Starter #1
The wastegate on my GT-17 turbo seems to be sticking again. Symptoms include boosting into the red, then P1549 and base boost only. Modulation of the boost in the yellow zone is also pretty jerky.

For sure it was sticky to seized a few years ago, confirmed by attaching an air pump. I freed it up by spraying the shaft with good penetrant and it hasn't been an issue for a couple of years.

It's back. I can spray penetrant on the side of the wastegate with the actuator linkage, but on the other side it's just a smooth turbo housing.

  1. Has this happened to other people?
  2. Would dropping the downpipe for a better look be the next step?
 

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Discussion Starter #2
According to my local Saab shop, penetrating oil is the way to do it. If that doesn't help, a turbo rebuild. :confused:


I haven't had the time to hook up a bicycle pump to the actuating cylinder to view the movement of the wastegate with pressure. Hopefully this weekend.
 

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General Malfunction makes a really good high heat lube/penetrant that was originally developed to use on the old choke heat riser valves.

I have a spray can of it somewhere, I know for sure it is a white and blue Delco can, I've used it on wastegate pivot points with great success.
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General Malfunction makes a really good high heat lube/penetrant that was originally developed to use on the old choke heat riser valves.

I have a spray can of it somewhere, I know for sure it is a white and blue Delco can, I've used it on wastegate pivot points with great success.
.
General Malfunction That literally made me laugh out loud. That was a good one! Lol
 

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Discussion Starter #6 (Edited)
dismount the linkage (don´t loose the clip) and try to move the lever. There is no need to dismount the downpipe.
It's really hard to move by hand. At least when I tried it. The actuator actually puts out quite a lot of force. I'm not sure what I'd learn from trying to move it by hand.

General Malfunction makes a really good high heat lube/penetrant that was originally developed to use on the old choke heat riser valves.

I have a spray can of it somewhere, I know for sure it is a white and blue Delco can, I've used it on wastegate pivot points with great success.
.
GM Heat Riser Valve Lubricant. It's actually for the valves they put down at the bottom of one exhaust manifold on a V8 to make the gas flow across passages in the intake manifold and heat that up.

And yes, that's exactly what I'm using, white can. I'll get a pic later maybe. ;ol;
 

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Discussion Starter #8
Well, for sure it was stuck. I hooked up my bicycle pump (the Schraeder chuck actually holds onto the nipple on the actuator canister) and a lot of pressure barely budged it.

Okay, I used small Channellock pliers to move the arm. It was really sticky and grunchy the first couple of times I moved it, then it freed up perfectly. :confused::roll:. Because I did not remove the linkage (the pliers can grab the arm lengthwise with the link on), I can't swear that the problem was with the wastegate and not the actuator. I also took off the control valve, and tested it and a spare I have. Both worked fine.

Anyway, I sprayed down everything that could possibly rust with the magic GM penetrating fluid/lubricant, checked the action with my bicycle pump, and put everything back together. Going for a drive, boost limitation works perfectly and the car runs much nicer under boost.

For those who are wondering how this works, on a GT17 turbo, the wastegate is pretty much full open if the actuator is fed around 10 PSI, maybe 12 PSI. At lower pressures, it's correspondingly open less. It seems to start to move at quite low pressure, maybe 2 PSI.

If you plumbed the wastegate actuator to the post-turbo, pressurised intake tract, it would probably limit your boost severely, 8 PSI is my guess.

Instead, Saab set up a three-way valve. The bottom nozzle of the valve is connected to the pressurised side of the intake. The middle nozzle is connected to the wastegate actuator. The top nozzle is connected to the post-MAF, pre-turbo unpressurized intake tract (via another hose which is probably part of the evaporative emissions system).

By default, the valve connects the lower nozzle with the middle nozzle, which means that even slight boost pressure will start opening the wastegate. However, if you apply +12V to the control valve, it clicks and connects the top nozzle with the middle nozzle. This means that the wastegate actuator sees, at most, atmospheric pressure, and closes right up. (I suspect less than atmospheric due to venturi effect where the hose plumbs into the intake.)

So the computer sends a signal to the valve, valve takes the pressure away from the actuator, and you get full boost. Modulate the valve to keep the desired boost level. Simple! ;ol;
 
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