Low boost at high rpms

Chuci · **Posted:** Wed Jan 20, 2021 2:20 pm

New turbo is in the car is running smooth except for the fact that at higher rpms I am getting low boost. I did notice that my breather tube for my ccv valve has a rip, could that be the problem?

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

It should not be, no. But any leaks between the turbo outlet and the throttle body could cause this. Leaks on the pressure side are very bad for the turbo - you do not want to run this way or you risk overspeeding the turbo and causing severe damage. You could also have a problem with the vane control on the turbo or *possibly* an exhaust obstruction.

Chuci · **Posted:** Wed Jan 20, 2021 3:07 pm

thesameguy wrote:

It should not be, no. But any leaks between the turbo outlet and the throttle body could cause this. Leaks on the pressure side are very bad for the turbo - you do not want to run this way or you risk overspeeding the turbo and causing severe damage. You could also have a problem with the vane control on the turbo or *possibly* an exhaust obstruction.

My intake hose that connects to my turbo was ripped a bit could that be something?

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

No, the inlet to the turbo will not affect boost. Only plumbing after the turbo, not before.

Chuci · **Posted:** Wed Jan 20, 2021 4:34 pm

What do you recommend I do?

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

You need to determine whether you have a boost leak, a problem with vane actuation, or a blockage in the exhaust. Is the CEL illuminated? I would think a low boost issue would trigger a CEL.

Chuci · **Posted:** Wed Jan 20, 2021 6:12 pm

thesameguy wrote:

You need to determine whether you have a boost leak, a problem with vane actuation, or a blockage in the exhaust. Is the CEL illuminated? I would think a low boost issue would trigger a CEL.

My check engine light has been on since I got the car. The previous owner messed up a lot of stuff. I’ll go see what codes I have.

WWDiesel · **Posted:** Wed Jan 20, 2021 9:25 pm

thesameguy wrote:

No, the inlet to the turbo will not affect boost. Only plumbing after the turbo, not before.

Not entirely true, if the hose came apart and covered the inlet vanes with debris or worse yet blew stuff into the the Charge Air Cooler (CAC/intercooler) and stopped up the flues, it could very well negatively affect boost pressure especially when the turbo is calling for higher demand.
That is the way to stop a run-a-way diesel, you stuff something into the suction of the turbo real quick to choke off the air flow to the engine and thus shut it down.
Variable vane issues like sticking vanes that won't fully operate to max or a bad turbo modulator valve, or low vacuum to the controller, or a leaking or cracked pipe from anywhere in the vacuum system to the modular valve can also limit boost pressure in a big way.
Another possibility is a partly stopped up CAT which will raise backpressure so high on the outlet side of the turbo that it can not make full boost pressure.

Chuci · **Posted:** Wed Jan 20, 2021 9:28 pm

WWDiesel wrote:

thesameguy wrote:

No, the inlet to the turbo will not affect boost. Only plumbing after the turbo, not before.

Not entirely true, if the hose came apart and covered the inlet vanes with debris or worse yet blew stuff into the the Charge Air Cooler (CAC/intercooler) and stopped up the flues, it could very well negatively affect boost pressure especially when the turbo is calling for higher demand.
That is the way to stop a run-a-way diesel, you stuff something into the suction of the turbo real quick to choke off the air flow to the engine and thus shut it down.
Variable vane issues like sticking vanes that won't fully operate to max or a bad turbo modulator valve, or low vacuum to the controller, or a leaking or cracked pipe from anywhere in the vacuum system to the modular valve can also limit boost pressure in a big way.
Another possibility is a partly stopped up CAT which will raise backpressure so high on the outlet side of the turbo that it can not make full boost pressure.

That could be the issue. I think I’m just gonna go through everything and see how it goes

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

If something went into the inlet of the turbo, that turbo is done for. The blades are extremely delicate - they will not survive any sort of impact. If something went in, and then through into the intercooler, that damage would be very obvious, and you're shopping for a new turbo. That looks like this:

Chuci · **Posted:** Fri Jan 22, 2021 6:04 am

thesameguy wrote:

If something went into the inlet of the turbo, that turbo is done for. The blades are extremely delicate - they will not survive any sort of impact. If something went in, and then through into the intercooler, that damage would be very obvious, and you're shopping for a new turbo. That looks like this:

If anything I have a warranty on the turbo, the worst part would be installing it.

Sent from my iPhone using Tapatalk

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

Warranty won't cover abuse... If there's concern something went through the turbo, remove the inlet ducting and inspect!

Chuci · **Posted:** Sat Jan 23, 2021 1:06 am

thesameguy wrote:

Warranty won't cover abuse... If there's concern something went through the turbo, remove the inlet ducting and inspect!

You’re right. I did get a quick look today at the turbo I didn’t remove it or anything but it did look fine. I do think something is in the CAT. I’m waiting for my day off to take everything apart again.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

If it looks fine it likely is. Why do you think you have low boost? A code? Live data? A boost gauge?

Chuci · **Posted:** Mon Jan 25, 2021 8:19 pm

thesameguy wrote:

If it looks fine it likely is. Why do you think you have low boost? A code? Live data? A boost gauge?

I’m thinking I have stuff in my CAT as when I blew my turbo it did shoot a bunch of stuff out into the exhaust

WWDiesel · **Posted:** Mon Jan 25, 2021 10:25 pm

Best to get rid of the CAT and the choke point right in front of it if you can.
Replace all of it with a piece of 2.5" exhaust pipe and never look back.
Your engine and turbo will thank you for it! :BANANA:

Chuci · **Posted:** Tue Jan 26, 2021 1:10 am

WWDiesel wrote:

Best to get rid of the CAT and the choke point right in front of it if you can.
Replace all of it with a piece of 2.5" exhaust pipe and never look back.
Your engine and turbo will thank you for it! :BANANA:

As for short term do you think I can just hollow out the catalytic converter?

WWDiesel · **Posted:** Tue Jan 26, 2021 2:24 am

Chuci wrote:

WWDiesel wrote:

Best to get rid of the CAT and the choke point right in front of it if you can.
Replace all of it with a piece of 2.5" exhaust pipe and never look back.
Your engine and turbo will thank you for it! :BANANA:

As for short term do you think I can just hollow out the catalytic converter?

Absolutely! Have busted out the guts of many a CAT over the years and put them back on. :lol:

Chuci · **Posted:** Tue Jan 26, 2021 1:03 pm

WWDiesel wrote:

Chuci wrote:

WWDiesel wrote:

Best to get rid of the CAT and the choke point right in front of it if you can.
Replace all of it with a piece of 2.5" exhaust pipe and never look back.
Your engine and turbo will thank you for it! :BANANA:

As for short term do you think I can just hollow out the catalytic converter?

Absolutely! Have busted out the guts of many a CAT over the years and put them back on. :lol:

Alright thanks! You’ve been a great help. If I have anything else I will ask.

thesameguy · **Joined:** Sat Oct 01, 2016 8:24 pm **Posts:** 652

If the cat is still good, you might see if you can sell it. Used cats can be worth quite a bit of money. I parted out a Jaguar XJ8 a few years ago and got more money for the two cats from a recycler than I paid for the whole car.

Low boost at high rpms

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