Can I run a twin turbo setup with one turbo not connected?

[james6546]

Hey,

I m at my wits end trying to diagnose a whistling noise that my 3000GT makes under boost. It s like turbo noise x10.

It made the noise when I bought it, but then I did a load of work -GFB blow off valve, new intake gaskets, exhaust gaskets, head gasket, got a crack in the manifold welded and welded a crack in the downpipe. One of these things solved it, but over the last 2k miles it has slowly come back.

I ve tested the intercooler pipes with a smoke machine, inspected the manifold for cracks, changed the throttle body gasket etc., but nothing makes any difference.

I ve got one thing do to, change the throttle body bushings, but I don t think they are the issue.

For diagnosis, can I disconnect one of the turbo loops and just have it venting into the air and just have one turbo connected to the intake? I don t want the disconnected turbo to overboost or do anything that would cause any damage.

[richhead]

how can it overboost if its not connected to the inlet?

[OldGermanHeaps]

It might overspeed if it never gets enough boost built up to open the wastegate, and it will make a ton of noise which wont hely your diagnosis efforts surely?
Maybe wedge the wastegate wide open if you are going to try that.

[james6546]

richhead said:

how can it overboost if its not connected to the inlet?

Sorry, meant over speed. Not a turbo expert!

[xstian]

Can you not just pressurise the inlet system and associated pipes and intercooler to try and replicate the noise.

[Huntsman]

I did 10 yeaes in turbo design.

I wouldn't run it with no load on the intake side of a turbo the overspeed is too risky.

[s p a c e m a n]

Anyone doing power runs at a Dyno local to you? Most are up for a bit of diagnosis as long as the cars not going to explode, stick it on there and run it with the bonnet open.

[stevieturbo]

s p a c e m a n said:

Anyone doing power runs at a Dyno local to you? Most are up for a bit of diagnosis as long as the cars not going to explode, stick it on there and run it with the bonnet open.

But you don't know if it's going to explode, and having your head under there when it does.....might not go well. But they can make good videos for youtube
But it could certainly be helpful if they allowed you to do this

If you have properly pressurised the entire system and are sure it is not leaks....

It could be a turbo with damage, as they can whistle although eventually they die. So depends how long it's been going on for.

Does the impeller and turbine discharge look ok ? spins ok ? no visible damage or excessive play ?

Air leak should generally be fairly easy to find though if it's making that much noise.

Does the car actually perform ok ? making correct boost etc ?

[james6546]

Ok, I’ll try and answer all of the questions:

- dyno has crossed my mind, I’d be unlucky if it explodes, I’ve done about 500 miles with it like this. It drives fine but is slightly low on power. I’ll make that plan C.

- I won’t do my disconnecting turbo idea then if it risks damaging anything, thanks

- I’ve tried pressurising as much I can of the system, but I suspect it’s either the intake manifold/throttle body side, or the exhaust manifold side, neither of which I can test with the pressure thingy.

So far I have found one loose jubilee, not that tight exhaust manifold nuts and the throttle body gasket on backwards, all of which I was certain was the issue until I drove it!

I think my next step is removing the rear turbo and exhaust manifold as I reckon I can smell exhaust gas slightly in that area. That’s a nightmare of a job though so I’m trying to avoid it!

Picture for reference (and some sympathy)

[james6546]

stevieturbo said:

s p a c e m a n said:

Anyone doing power runs at a Dyno local to you? Most are up for a bit of diagnosis as long as the cars not going to explode, stick it on there and run it with the bonnet open.

But you don't know if it's going to explode, and having your head under there when it does.....might not go well. But they can make good videos for youtube
But it could certainly be helpful if they allowed you to do this

If you have properly pressurised the entire system and are sure it is not leaks....

It could be a turbo with damage, as they can whistle although eventually they die. So depends how long it's been going on for.

Does the impeller and turbine discharge look ok ? spins ok ? no visible damage or excessive play ?

Air leak should generally be fairly easy to find though if it's making that much noise.

Does the car actually perform ok ? making correct boost etc ?

The turbos both seem fine, no play at all.

It’s a bit down on power I would say.

What actually happened was I did a launch while on a road trip, the car stumbled and some smoke came out of the exhaust and it’s been doing this since, so kind of makes sense I’ve blown a hose, I just can’t find it!

There are a couple of hoses I still need to test but it involves getting the under tray off which is a nightmare in itself due to the active aero

[Doesitdrive]

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

[james6546]

Doesitdrive said:

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

Tried that, no smoke other than out of the throttle body bushes.

I think next I’ll try smoke and pressurising the system

[Doesitdrive]

james6546 said:

Doesitdrive said:

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

Tried that, no smoke other than out of the throttle body bushes.

I think next I ll try smoke and pressurising the system

Should throttle body bushes be letting air in or out?

[james6546]

Doesitdrive said:

james6546 said:

Doesitdrive said:

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

Tried that, no smoke other than out of the throttle body bushes.

I think next I ll try smoke and pressurising the system

Should throttle body bushes be letting air in or out?

No, I’ve got a new set to go on in my lunch break from work. I’m not sure they are the cause of the issue though

[Doesitdrive]

james6546 said:

Doesitdrive said:

james6546 said:

Doesitdrive said:

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

Tried that, no smoke other than out of the throttle body bushes.

I think next I ll try smoke and pressurising the system

Should throttle body bushes be letting air in or out?

No, I ve got a new set to go on in my lunch break from work. I m not sure they are the cause of the issue though

If you haven't found anything else you may be in for a surprise.

[james6546]

Doesitdrive said:

If you haven't found anything else you may be in for a surprise.

I didn’t manage it, I forgot that the throttle body housing is water cooled, I’m not messing with that in my lunch break!

[stevieturbo]

Plug the exhaust, plug the compressor intake, pressure test the entire system in lieu of being able to close all the intake valves and pressurising the intake side alone.

Obviously you will get some leakage past the pistons/rings and a few other areas, but you should still be able to generate decent pressure in the entire system, and this way you are testing the entire system

[james6546]

stevieturbo said:

Plug the exhaust, plug the compressor intake, pressure test the entire system in lieu of being able to close all the intake valves and pressurising the intake side alone.

Obviously you will get some leakage past the pistons/rings and a few other areas, but you should still be able to generate decent pressure in the entire system, and this way you are testing the entire system

Thanks, I’ll try that.

Coincidentally I’m having the massive holes in the exhaust repaired tomorrow, so that will help!

[Heaveho]

james6546 said:

Doesitdrive said:

james6546 said:

Doesitdrive said:

A smoke machine? It finds leaks better than anything else.
Use it a lot these days,

Tried that, no smoke other than out of the throttle body bushes.

I think next I ll try smoke and pressurising the system

Should throttle body bushes be letting air in or out?

No, I ve got a new set to go on in my lunch break from work. I m not sure they are the cause of the issue though

In my admittedly limited experience of this, the throttle body bushings may leak a bit on closed throttle, and seal when open and pressure is applied. I found this out when, out of interest, I pressurised the system with a home made set up. Mitsubishi Evo for reference. I didn't do mine, the general consensus was not to bother. However, there wasn't a problem with my car that I was trying to solve when this became apparent. As part of the process of elimination, in your case, it might be worth the effort.

Edited by Heaveho on Monday 27th July 20:18