Volvo 760 turbo, overboost problem.

[MasterHachiRoku]

I noticed that when I accelerate hard in my 760, the boost needle needle pegs the end of the gauge, I quickly back off the throttle when it does that and I've been trying to drive really easy to prevent it from boosting to much and avoid pinging and hitting the overboost switch. How far should the needle go on the boost gauge? I can't imagine it should go all the way past the end of the gauge (only did that once.) The car is bone stock, driven by 90 year old man before me. I replaced the vacuum line that runs from the wastegate to the intake manifold and it still overboosts. This car has the mitsubishi turbo that has the internal wastegate at the front of the turbo and I'm suspecting that the wastegate it stuck, allowing more boost than there should be.
Do I need to remove the wastegate and clean it out with some degreaser or can I just spray some with it still on there? What else can I do to get it unstuck? I figured I want to deal with this issue while I'm changing the radiator before putting everything back together. What else could this overboost problem be? The only other turbo car I've worked on is my brothers 240sx sr20det swap and that had an external wastegate.

Thanks,
Jacob

[atrokz]

Q:

What year, and what mods.

I'm assuming this does not have a "Turbo+" kit factory installed?

[MasterHachiRoku]

It's a bone stock 1988 Volvo 760 Turbo Intercooler.

[Simi]

Well just go down the line, the wastegate to the turbo, the cbv, and the line going to the intake.

Double check all those for leaks or problems

[MasterHachiRoku]

Originally Posted by Simi

Well just go down the line, the wastegate to the turbo, the cbv, and the line going to the intake.

Double check all those for leaks or problems

The only vacuum line on the wastegate is the one that runs to the intake manifold, nothing that runs to the turbo.

[MasterHachiRoku]

Is there a vacuum diagram anywhere for this car?

[MrBill]

Is the vacuum line going to the wastegate in an intake manifold port?
I once tried to use the ports on the throttle body and the holes underneath the vac ports were so small they didn't flow enough to engage the wastegate.

Do you have an air compressor or pressure pump or something? The diaphram may be torn which is something you probably wouldn't hear if the motor is running.

Test the setup with compressor air turned down to like 20-30 psi and see what happens.

[MasterHachiRoku]

Originally Posted by MrBill

Is the vacuum line going to the wastegate in an intake manifold port?
I once tried to use the ports on the throttle body and the holes underneath the vac ports were so small they didn't flow enough to engage the wastegate.

Do you have an air compressor or pressure pump or something? The diaphram may be torn which is something you probably wouldn't hear if the motor is running.

Test the setup with compressor air turned down to like 20-30 psi and see what happens.

The line goes to an intake manifold port, not the throttle body.
If the diaphram is torn, do I need to replace the whole wastegate, or is there a wastegate rebuild kit or something?
I'll make a video to show you guys what I'm dealing with.

[2manyturbos]

^^ You are probably looking at the vacuum line for the bypass valve. See if there is a vacuum line running from the turbo compressor housing down to the waste gate actuator. And no, if the diaphram in the actuator is torn, there is no rebuild kit for one. You need to buy another actuator.

[MasterHachiRoku]

Here's the quick video I made:
http://www.youtube.com/watch?v=zAq02...ature=youtu.be

[MasterHachiRoku]

BTW even though there is a lot of oil around the turbo, the car does NOT smoke one bit like a blown turbo would cause, kinda weird.

[red740t]

put a real gauge on it. the factory gauge sucks. the waste gate hose should go from the wg actuator to the compressor housing, check that hose. Fuel comes on at 12 psi. If your not hitting fuel cut then just leave it alone and have fun. that engine will run forever at 12 psi

[Steve940Estate]

As said the wastegate actuator is operated by a line from the turbo itself and the line from the intake is for the bypass valve.
Check the pipe and make sure it's not split, check the wategate actuator to see if the diaphragm still works. You might move it by blowing on a piece of tube or you could connect a bicycle pump to it and carefully try it that way.

On my car you get around 12psi when the gauge goes to the end of the scale.

[MasterHachiRoku]

In the video I show the hose that goes from the compressor housing to the wastegate, and it looks fine. I will definitely hook up an actual boost gauge and see how much boost I am pushing. I'm just worried about damaging the engine from too much boost. When I first got the car it would ping really badly and cut power if you got past 3,500rpm's under load, but after an oil change and fresh 93 fuel it doesn't seem to do it anymore. But it's still clearly boosting way too much.

[MasterHachiRoku]

Well I got the car up and running again with the new radiator. Anyway, its still overboosting, If I lay into it, the boost will just keep climbing all the way to the end of the gauge, as if its infinite boost. Is this for sure a torn wastegate actuator diaphragm or can it be anything else?

Thanks,
Jacob

[MrBill]

Did you pressurize that line like I suggested? If you get a little hand pump (or regulated compressor) you can give the actuator some pressure and see what's happening.

Either way, you'll probably end up needing to R&R the actuator or both the actuator and wastegate housing if the swingvalve is siezed, which is integrated in the turbine housing. I've never seen a seized swingvalve though.

But, if you give it ~7-8 psi and it moves like you'd expect, there's something wrong with the line from the compressor.

[MasterHachiRoku]

I hooked up an actual boost gauge to it and took it for a drive.
With foot to the floor it holds 12psi until around 3800-4000RPM's it spikes to 14psi and pings a little followed by the overboost switch kicking in.
Any suggestions on what I should do about this? Change the wastegate? Can I adjust the timing by moving the distributor on the back of the engine to better tune the car for this boost?
Keep in mind the car is absolutely bone stock and is running the TD05 turbo...

Thanks,
Jacob

[XxJenoxX]

Did you change the fuel filter? I had very similar ping issues, and the filter was clogged. Frequently overlooked maintenance for these cars, so do it if you haven't.

[nickm]

Originally Posted by MasterHachiRoku

I hooked up an actual boost gauge to it and took it for a drive.
With foot to the floor it holds 12psi until around 3800-4000RPM's it spikes to 14psi and pings a little followed by the overboost switch kicking in.
Any suggestions on what I should do about this? Change the wastegate? Can I adjust the timing by moving the distributor on the back of the engine to better tune the car for this boost?
Keep in mind the car is absolutely bone stock and is running the TD05 turbo...

Thanks,
Jacob

If the car is standard.... and is making 12psi something is wrong.
If the line between the waste gate and compressor was leaking a little. It could act like a bleed valve.
You should be seeing 7-9psi. Not more. Fix this first. You have allot of oil round there the hose could be perished.
At 12-13psi the over boost will cut in.

Yes turning the distributor will pull timing But it will not solve your problem.