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Boost Builds Well Then Dies

MrStabby

By MrStabby,
in Engines & Forced Induction

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MrStabby Grand Master

MrStabby

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Dead turbos were recently replaced with highflows and xforce dumps by an amateur (me). Giving it a thrash for the first time at the track today - in third the boost is normal (currently 13psi) until 6000rpm then it drops straight down to ~ 8psi. In fourth it the same thing happens at about 5500rpm. Happens every time like clockwork. Boost gauge just falls back to 8 and engine feels really soft. EBC has a greddy box in the cabin and a profec box in the engine bay....Any ideas what would cause this?

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MrStabby Grand Master

MrStabby

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Yeah its a 32 GTR (look left :-)

The actuators came off the old turbos (which were working) but the spring in one did seem stiffer than the spring in the other. I do have two spare actuators, but i'm not sure of the condition.

So what do you think is happening? Could it be that when the wastegate opens it snaps open all way so bleeds off too much exhaust?

To test, i guess i should apply vacuum (or boost?) to each actuator and watch how the rod moves, right? What tool would I use to apply the signal and where do i get it?

BTW - thanks all for the input.

saliya Rising Star

saliya

Posted
Posted
Yeah its a 32 GTR (look left :-)

The actuators came off the old turbos (which were working) but the spring in one did seem stiffer than the spring in the other. I do have two spare actuators, but i'm not sure of the condition.

So what do you think is happening? Could it be that when the wastegate opens it snaps open all way so bleeds off too much exhaust?

To test, i guess i should apply vacuum (or boost?) to each actuator and watch how the rod moves, right? What tool would I use to apply the signal and where do i get it?

BTW - thanks all for the input.

The service manual recommends using an air gun with compressed air regulated to 11-13 psi (testing pressure of the source first) and blowing it straight in the hose on the top of the actuator.

You also want to verify that it opens/closes all the way; without being able to see the flap and/or having a point of reference that will be harder.

I don't know much about your boost controller; does it have different settings for different gears or overboost protection?

Regards,

Saliya

MrStabby Grand Master

MrStabby

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Any damage to the engine when the turbos let go, and that would be stock turbos right ???

And at what boost?

Stock turbos, no damage to motor, 13 psi, conservative tune, 11.5 AFR. The turbos were probably 118,000kms old (supposed to be replaced at 100,000 according to Nissan).

MrStabby Grand Master

MrStabby

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Ok both turbo actuators are moving in unison, so it looks like they're ok.

The EBC unit is a greddy profec, I found some instructions HERE

So i guess i'll just go through the setup procedure again. It does have a safety feature that drops boost back down to stock level, so i must be hitting that.

Thanks again.

mad082 Grand Master

mad082

Posted
Posted

did the exhaust wheel happen to come off the old turbos at all? if so it may have damaged the cat. a mate of mine had a similar problem where boost was dropping at higher rpm. turned out to be his cat was damaged (rear section had broken off and turned sideways and was blocking the exhaust)

also to check the EBC, i would just disconnect it and try to borrow someones manual controller that is set to a similar boost pressure. if it still drops pressure it isn't the EBC

MrStabby Grand Master

MrStabby

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did the exhaust wheel happen to come off the old turbos at all? if so it may have damaged the cat. a mate of mine had a similar problem where boost was dropping at higher rpm. turned out to be his cat was damaged (rear section had broken off and turned sideways and was blocking the exhaust)

also to check the EBC, i would just disconnect it and try to borrow someones manual controller that is set to a similar boost pressure. if it still drops pressure it isn't the EBC

Yeah the wheel disintegrated, and i removed a fair bit of ex-turbine rubble from in front of the cat matrix (200 ci metalcat). There were no bits stuck in the front of the matrix itself, but i guess they could be lodged further down. I'll take a look at that if the EBC re-training doesnt work.

lineskee 33 Community Regular

lineskee 33

Posted
Posted (edited)

im putting my money on it being the EBC. especially if it is a greddy, I have a mate with the exact same symptoms at the moment. It shouldnt be the wastegate unless u are running stupid amounts of boost through the car. And if it is the actuators sticking the wastegate shut, shouldnt the boost be creeping up not down?

Id say put on a manual boost controller, test to see if it changes how the car drives, and if it is the EBC then look up how to properly tune the EBC. There are threads in here somewhere.

:P

Edited by lineskee 33
MrStabby Grand Master

MrStabby

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im putting my money on it being the EBC. especially if it is a greddy, I have a mate with the exact same symptoms at the moment.

Has he tried re-running the learning procedure as per the manual i posted above? It says "this process must be done after the installation of Profec, and after any changes are made to the characteristics of the wastegate spring, or out put power of the engine (IE turbo size, intercooler)".

As far as i can tell in my case the Profec is working as designed and i'm just hitting the overboost protection because i've changed the turbos. I just didnt know this was required before i posted.

lineskee 33 Community Regular

lineskee 33

Posted
Posted

No he doesnt want to touch it. Sorry mate, i thought u had the newer model of the greddy ebc. with the profec B you just adjust the gain until the boost stops dropping off.

Are you able to increase the overboost value so that it doesnt kick in?

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