Jump to content
SAU Community

RB26 overboosting issue. Vacuum line plumbing help?

Kanaric

By Kanaric,
in Engines & Forced Induction

 Share

Recommended Posts

Kanaric Enthusiast

Kanaric

Posted
Posted (edited)

I got a R33 GTR and it has a Link G4 and N1 turbos with a MAC boost solenoid. 

After picking it up I noticed it was overboosting and brought it home and saw that vacuum lines had come off with split ends so i'm trying to figure out wtf they were doing here. 

The solenoid had only 1 line going in and i'm trying to figure out where the other one is. They have the stock route for the one that comes out of the top of the wastegate and that seems connected correctly. The line that comes out of the intake pipe next to that is blocked off with a rubber stopped, same on the other side, so they are using some alternative setup.

I found two vacuum lines that were not connected obviously i'm assuming more can be f**ked up. One of them comes from the back of the intake plenum. There are two large hoses and then a small 3rd one in the rear. It looks like it could go into the boost solenoid but any diagram I see it's supposed to go into some "water tube" that I can't seem to find. 

 

Here's some images to help out.

RB26+Vacuum+Diagram+2019.png

 

 

In this image the green is as stock and the blue is missing.

post-8901-1212837949.jpg

In this image the 'water tube' line is the vacuum line I think they may have been using for the boost solenoid

 

The other thing that wasn't attached goes to some T connector because they were zip tied together that made it obvious. This isn't on that diagram but it looks like it comes out of the 'bottom collector boost source' that is on the upper right of that top image.

 

I'm just trying to figure this shit out and whatever info or tips someone can provide would be useful but i'm wondering, does that 'water tube' vacuum line make sense as an alternative thing to use for a boost solenoid? And what is the 'bottom of the collector - boost source' thing on the upper right of the image used for and any guesses on why some T connector would be put on it? 

Anything i've touched before this was simple af dumbass straight forward shit and I don't really know these GTRs that well so any help is appreciated. My last car was a simple stock mount turbo upgrade gtst setup lol. 

 

edit: I tried that plenum line for the solenoid and it overboosts. It's like as if the wastegate is getting no indication of boost pressure. Just will go until fuel cut if I let it so something is not connected right. 

Edited by Kanaric
Duncan Grand Master

Duncan

Posted
Posted

When you say "picked it up" do you mean it is new to you or it is back from a shop that changed something?

The required plumbing is pretty simple, anything else that is open needs to be blocked off.

You need a post throttle body pressure source to the boost controller (in this case the Link). There is a nipple on the back of the engine which is suitable, the stock line from there runs to the standard boost gauge sender on the firewall (you would also T to this for any boost gauge/logger etc). It is mentioned but not marked on your first diagram

You then need a plenum (pre throttle) boost source which goes to the boost control valve inlet, and then the boost control valve outlet is attached to both wastegates (the green line). An alternative (much shorter) option is to take this source from any point after the 2 turbo outlets merge and run straight to the boost control valve mounted on the passenger side, then back to both wastegates, this can reduce spiking due to the shorter runs

There are separate vacuum feeds to the carbon canister, fuel pressure regulator, BOVs, brake/clutch boosters and also PCV, AAC etc, none of them should need to be touched. But any vacuum line that is open to atmosphere needs to be blocked. The "water tube" has separate lines with both water and air so it is a misleading name.

  • Like 1
Kanaric Enthusiast

Kanaric

Posted
  • Author
Posted (edited)
On 11/17/2021 at 1:02 PM, Duncan said:

When you say "picked it up" do you mean it is new to you or it is back from a shop that changed something?

The required plumbing is pretty simple, anything else that is open needs to be blocked off.

You need a post throttle body pressure source to the boost controller (in this case the Link). There is a nipple on the back of the engine which is suitable, the stock line from there runs to the standard boost gauge sender on the firewall (you would also T to this for any boost gauge/logger etc). It is mentioned but not marked on your first diagram

You then need a plenum (pre throttle) boost source which goes to the boost control valve inlet, and then the boost control valve outlet is attached to both wastegates (the green line). An alternative (much shorter) option is to take this source from any point after the 2 turbo outlets merge and run straight to the boost control valve mounted on the passenger side, then back to both wastegates, this can reduce spiking due to the shorter runs

There are separate vacuum feeds to the carbon canister, fuel pressure regulator, BOVs, brake/clutch boosters and also PCV, AAC etc, none of them should need to be touched. But any vacuum line that is open to atmosphere needs to be blocked. The "water tube" has separate lines with both water and air so it is a misleading name.

I picked it up from a shop who did bodywork and fully redid the paint, and this is like a state away because I live in the middle of nowhere. They claimed the car ran fine when I picked it up. I drove it and it did but I had to drive 6 hours to get home and it had these problems starting during that trip. So something went wrong during that. 

Whoever did this changes from stock blocked off the stock 'nipples' they were no longer using. 

The inlet on the boost control solenoid is one of what was missing. 

that water tube air line that comes from the plenum, stock, is one that was hanging loose with a cracked end and is exactly long enough so I wasn't sure if they were instead using that for the boost controller. Where is this 'water tube' inlet for that? I wanted to see if that was blocked off or rerouted to confirm but I can't find that. It fits the 'pre throttle boost source' if so. 

The one from the back of the engine was Td up for something, i do not have an extra boost gauge or anything, so i'll trace that out and see if maybe they were using that. 

Thanks for the info. 

 

Quote

An alternative (much shorter) option is to take this source from any point after the 2 turbo outlets merge and run straight to the boost control valve mounted on the passenger side, then back to both wastegates, this can reduce spiking due to the shorter runs

I've been considering doing it like this but I want to make sure I catch if anything is messed up.

 

edit: they put a T on the fuel pressure regulator line for a map sensor. 

Edited by Kanaric
GTSBoy Grand Master

GTSBoy

Posted
Posted
On 11/18/2021 at 8:52 AM, Kanaric said:

edit: they put a T on the fuel pressure regulator line for a map sensor.

Not the smartest place to interfere with the vacuum lines because if you manage to have a problem (ie, it falls off/open) you get uncontrolled boost at the same time that you don't get boost referenced fuel pressure. Ideal for rapidly beating the engine to death.

  • Like 1
joshuaho96 Veteran

joshuaho96

Posted
Posted
On 11/17/2021 at 2:53 PM, GTSBoy said:

Not the smartest place to interfere with the vacuum lines because if you manage to have a problem (ie, it falls off/open) you get uncontrolled boost at the same time that you don't get boost referenced fuel pressure. Ideal for rapidly beating the engine to death.

I've never understood why people do this when there is a dedicated fitting on the back of the balance tube for the factory boost gauge.

  • Like 1
GTSBoy Grand Master

GTSBoy

Posted
Posted
On 11/18/2021 at 10:15 AM, joshuaho96 said:

I've never understood why people do this when there is a dedicated fitting on the back of the balance tube for the factory boost gauge.

It's because it is the easiest to see and touch. Do not underestimate the laziness and stupidity of your typical Skyline modifier.

  • Like 1
joshuaho96 Veteran

joshuaho96

Posted
Posted (edited)

Regarding this picture:

post-8901-1212837949.jpg

 

The leftmost hose barb is for boost control. The "water tube assembly" you're talking about has both vacuum lines and coolant pipes. That is the green line pictured on the vacuum diagram labeled as the boost source. The second from the left is the air feed for the cold start air valve, Nissan calls it an intake air regulator. That's a valve with a bimetallic strip in it that closes as it heats up. This piece is right under the intake manifold and is basically impossible to get to without pulling everything else off first. The rightmost is the AAC valve air feed as you have mentioned.

The factory system is super basic bleed-style, when the solenoid opens it is bleeding the green boost source line to the rear turbo pre-compressor inlet, the wastegate actuator sees less boost as a result and doesn't open as far. As for how you should set up your MAC (presumably 3 port) solenoid, I would reference this article which details it pretty well: https://www.onpointdyno.com/boost-control-plumbing-get-it-right-save-money/

My entire intake side of the engine is still in pieces scattered across the garage so I can easily take photos of all this crap if need be, including how the lines should be and what they should look like. Keep in mind there are special orientations for a lot of these hoses, the manual likes to make mention of this multiple times.

Edited by joshuaho96

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • RP1421
      S15 Spec R

      By RP1421 · Posted

      As discussed in the previous post, the bushes in the 110 needed replacing. I took this opportunity to replace the castor bushes, the front lower control arm, lower the car and get the alignment dialled in with new tyres. I took it down to Alignment Motorsports on the GC to get this work done and also get more out of the Shockworks as I felt like I wasn't getting the full use out of them.  To cut a very long story short, it ended up being the case the passenger side castor arm wouldn't accept the brand new bush as the sleeve had worn badly enough to the point you could push the new bush in by hand and completely through. Trying a pair of TRD bushes didn't fix the issue either (I had originally gone with Hardrace bushes). We needed to urgently source another castor arm, and thankfully this was sourced and the guys at the shop worked on my car until 7pm on a Saturday to get everything done. The car rides a lot nicer now with the suspension dialled in properly. Lowered the car a little as well to suit the lower profile front tyres, and just bring the car down generally. Eternally thankful for the guys down at the shop to get the car sorted, we both pulled big favours from our contacts to get it done on the Saturday.  Also plugged in the new Stedi foglights into the S15, and even from a quick test in the garage I'm keen to see how they look out on the road. I had some concerns about the length of the LED body and whether it'd fit in the foglight housing but it's fine.  I've got a small window coming up next month where I'll likely get a little paint work done on the 110 to remove the rear wing, add a boot wing and roof wing, get the side skirt fixed up and colour match the little panel on the tail lights so that I can install some badges that I've kept in storage. I'm also tempted to put in a new pair of headlights on the 110.  Until then, here's some more pictures from Easter this year. 
    • joshuaho96
      R32 GTS (RB20DE) Injectors Replacement

      By joshuaho96 · Posted

      I would put a fuel pressure gauge between the filter and the fuel rail, see if it's maintaining good fuel pressure at idle going up to the point when it stalls. Do you see any strange behavior in commanded fuel leading up to the point when it stalls? You might have to start going through the service manual and doing a long list of sensor tests if it's not the fuel system for whatever reason.
    • perry_r33
      R34 GTR Vspec Garage Sale - All must go!

      By perry_r33 · Posted

      Pm sent 
    • Robot
      Skyline v36 350GT sedan hunting on idle

      By Robot · Posted

      Hi,  Just joined the forum so I could share my "fix" of this problem. Might be of use to someone. Had the same hunting at idle issue on my V36 with VQ35HR engine after swapping the engine because the original one got overheated.  While changing the engine I made the mistake of cleaning the throttle bodies and tried all the tricks i could find to do a throttle relearn with no luck. Gave in and took it to a shop and they couldn't sort it. Then took it to my local Nissan dealership and they couldn't get it to idle properly. They said I'd need to replace the throttle bodies and the ecu probably costing more than the car is worth. So I had the idea of replacing the carbon I cleaned out with a thin layer of super glue and it's back to normal idle now. Bit rough but saved the car from the wreckers 🤣
    • GabsReDeal
      R32 GTS (RB20DE) Injectors Replacement

      By GabsReDeal · Posted

      After my last update, I went ahead with cleaning and restoring the entire fuel system. This included removing the tank and cleaning it with the Beyond Balistics solution, power washing it multiple times, drying it thoroughly, rinsing with IPA, drying again with heat gun and compressed air. Also, cleaning out the lines, fuel rail, and replacing the fuel pump with an OEM-style one. During the cleaning process, I replaced several hoses - including the breather hose on the fuel tank, which turned out to be the cause of the earlier fuel leak. This is what the old fuel filter looked like: Fuel tank before cleaning: Dirty Fuel Tank.mp4   Fuel tank after cleaning (some staining remains): Clean Fuel Tank.mp4 Both the OEM 270cc and new DeatschWerks 550cc injectors were cleaned professionally by a shop. Before reassembling everything, I tested the fuel flow by running the pump output into a container at the fuel filter location - flow looked good. I then fitted the new fuel filter and reassembled the rest of the system. Fuel Flow Test.mp4 Test 1 - 550cc injectors Ran the new fuel pump with its supplied diagonal strainer (different from OEM’s flat strainer) and my 550cc injectors using the same resized-injector map I had successfully used before. At first, it idled roughly and stalled when I applied throttle. Checked the spark plugs and found that they were fouled with carbon (likely from the earlier overly rich running when the injectors were clogged). After cleaning the plugs, the car started fine. However, it would only idle for 30–60 seconds before stalling, and while driving it would feel like a “fuel cut” after a few seconds - though it wouldn’t fully stall. Test 2 – Strainer swap Suspecting the diagonal strainer might not be reaching the tank bottom, I swapped it for the original flat strainer and filled the tank with ~45L of fuel. The issue persisted exactly the same. Test 3 – OEM injectors To eliminate tuning variables, I reinstalled the OEM 270cc injectors and reverted to the original map. Cleaned the spark plugs again just in-case. The stalling and “fuel cut” still remained.   At this stage, I suspect an intermittent power or connection fault at the fuel pump hanger, caused during the cleaning process. This has led me to look into getting Frenchy’s fuel hanger and replacing the unit entirely. TL;DR: Cleaned and restored the fuel system (tank, lines, rail, pump). Tested 550cc injectors with the same resized-injector map as before, but the car stalls at idle and experiences what feels like “fuel cut” after a few seconds of driving. Swapped back to OEM injectors with original map to rule out tuning, but the issue persists. Now suspecting an intermittent power or connection fault at the fuel pump hanger, possibly cause by the cleaning process.  
×
×
  • Create New...