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RB26 boost control vacuum line setup

joshuaho96
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joshuaho96 Veteran

joshuaho96

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image.thumb.png.fac575985dc178cd4fbd194e4a4284f9.png

I haven't looked at weird things people have done to RBs before so I don't really know what to make of this. Looking at the vacuum line just above the oil filter it looks like it's looped back on itself. Checking the vacuum diagram I'm pretty sure both ends of the loop are supposed to go to the OEM boost solenoid. OEM boost solenoid is nowhere to be found but the harness connector is still present and doesn't appear to be modified, couldn't find any boost solenoid at all. Wouldn't this be equivalent to 100% duty cycle on an OEM solenoid without the restrictor? Thankfully this isn't my car.

joshuaho96 Veteran

joshuaho96

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1 hour ago, r32-25t said:

Just block both those hoses, it wide open if they’re connected 

Ok, so I guessed right. Supposedly this car has -5s on it with the stock tune/ECU. Stock fuel injectors I confirmed personally. The owner told me it didn't start coming off the truck and when I checked it cylinder 4 is misfiring even at idle. 

BK Grand Master

BK

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Remember stock boost solenoid is a normally closed setup and then bleeds directly to atmosphere / air filter, so if you join both stock solenoid lines together it creates one hell of a vacuum leak.

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joshuaho96 Veteran

joshuaho96

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1 hour ago, Duncan said:

It would be worth tracing the wastegate solenoid boost reference source too.

As far as I can tell it's there is no wastegate solenoid anymore. I'm pretty sure that the brackets that hold the OEM solenoid on are also gone. The boost reference line is still hooked up like factory though, plenum line appears to go down to the combination vacuum + coolant pipe underneath. Checking the exhaust side of the engine it looks like the hoses are hooked up to the factory positions, both the wastegate line and the pre-compressor vent line. I couldn't get a clear view of the back of the engine because the autobahn88 hoses aren't clipped down or anything like the factory setup.

Duncan Grand Master

Duncan

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sorry, misleading extra word "solenoid" in my sentence :)

"It would be worth tracing the wastegate boost reference source too"

Sounds like the wastegates are connected directly to the post throttle source, so it should just be running wastegate pressure on the turbos. On standard that is about 12psi, if these are -5 they are more likely to have come with 14psi wastegates or 7. Apparently the boost is pretty lazy when hooked up that way, normally the boost controller holds the  pressure low until near the target boost level

joshuaho96 Veteran

joshuaho96

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13 minutes ago, Duncan said:

sorry, misleading extra word "solenoid" in my sentence :)

"It would be worth tracing the wastegate boost reference source too"

Sounds like the wastegates are connected directly to the post throttle source, so it should just be running wastegate pressure on the turbos. On standard that is about 12psi, if these are -5 they are more likely to have come with 14psi wastegates or 7. Apparently the boost is pretty lazy when hooked up that way, normally the boost controller holds the  pressure low until near the target boost level

Yeah, I told the owner to test the wastegate manually with a shop compressor and regulated air feed or some equivalent pressure source. We'll see how it goes I guess.

r32-25t Grand Master

r32-25t

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1 hour ago, Duncan said:

sorry, misleading extra word "solenoid" in my sentence :)

"It would be worth tracing the wastegate boost reference source too"

Sounds like the wastegates are connected directly to the post throttle source, so it should just be running wastegate pressure on the turbos. On standard that is about 12psi, if these are -5 they are more likely to have come with 14psi wastegates or 7. Apparently the boost is pretty lazy when hooked up that way, normally the boost controller holds the  pressure low until near the target boost level

No with that looped around it’s the same as having the wastegate line disconnected, they need to be blocked off 

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BK Grand Master

BK

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19 minutes ago, r32-25t said:

No with that looped around it’s the same as having the wastegate line disconnected, they need to be blocked off 

Almost yeah. The problem is the boost source that goes to the actuators is tee'd before the solenoid on the hard line and as I said the other side of the solenoid vents to airfliter, so if you just join the existing lines it's like a having a massive boost bleed on the actuator line. So much so that it'll bleed off that much to atmosphere the gates will never open because of such a weak boost signal at actuators.

Yes the lines need to be capped 👍

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