Jump to content
SAU Community

Only Rarely Makes Full Boost?

mattis96

By mattis96,
in Engines & Forced Induction

 Share

Recommended Posts

mattis96 Proficient

mattis96

Posted
Posted

Excuse the long story, so i'll try and keep it quick and to the point, i have tried googling first but to hard to pinpoint.

My boost is set to 18psi for high boost, 13psi low boost, although when driving it only hits 15psi most of the time. I went for a drive down a private road and it was making 18psi again ( which it hardly ever does this even though it is suppose to). Went driving around that road again later and still constantly maxing out at 15psi, with exactly the same driving style. Nothing was touched or changed between drives. The car doesnt feel like its struggling or choking, no flat spot with high boost, it just will hold at 15 psi through all gears.

What should i look for as I'd like to get back the 50+hp i am not making, and this was all setup at a workshop if that changes anything.

setup is RB25, Tial 44mm external gate with 1 bar spring, greddy profecb 2, gt3040, wolf v500.

Link to comment
https://www.sau.com.au/forums/topic/423381-only-rarely-makes-full-boost/
Share on other sites
benelli Rookie

benelli

Posted
Posted

Set your boost controller on high mode (18psi).

Your wastegate spring is set for 1 bar (~14.5psi-15psi) which means there is no way you will be able to hit 13psi.

15psi/1Bar is the lowest pressure you'll be able to run in your setup.

mattis96 Proficient

mattis96

Posted
  • Author
Posted

Why would it be a restriction in the pipe work for if sometimes it does reach full boost?

Pipe work is all stainless anyway, 3 inch from turbo to inter cooler all 1 piece, inter cooler to throttle body is 3 inch all 1 piece, 4 inch intake piping, 3.5 inch turbo back exhaust.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Hmmm.....simple things like rubber elbows that are under mechanical load and crimp off when hot. Or variations on the theme. Use your imagination.

Let's face it. If a turbo cannot reach even wastegate pressure then there can only be one a rather short list of things wrong. That would be;

Restriction in the turbo's inlet or outlet pipework.

Wastegate stuck open.

Massive boost leak.

/spoon

mattis96 Proficient

mattis96

Posted
  • Author
Posted

I don't know if it matters they are silicone joiners. I don't think it's a boost leak cause rarely it does make 18psi which is what it's set to, and I don't have a vacuum leak if its the same as boost leak?

I might not have worded my problem properly.

Lo boost is 13 psi and it stays on that no problem

Waste gate spring is 1 bar (14.7 psi if I remember correctly)

Hi boost is 18 psi but only reaches 15 (might be 14.7, to close on gauge to tell) but rarely does go to 18 :(

I don't want to go replacing parts cause knowing my luck the last thing I change it will be :(

So could it be waste gate stuck open? If it was I assume lo boost would be stuck on 1 bar (but it isn't)

Solenoid? But it does hold lo boost fine.

Anything else? Does the wolf v500 have a safety boost cut as it could be the map sensor?

I don't know...

Hanaldo Grand Master

Hanaldo

Posted
Posted

I'd be looking for boost leaks mate. Boost leaks aren't the same as vacuum leaks, if you have a split in a hose somewhere that seals itself under vacuum but leaks air at 15psi then that explains your problem.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Faulty boost controller is another option. If your wastegate is 14.7 psi and that's what it runs to when set on high boost, then the boost controller may be failing to do what it has to do (basically bleed enough air or otherwise limit the signal to the wastegate) so that you can go higher. If it does it sometimes and not others then you are looking for an intermittent problem, which is the sort designed to send you insane.

But, as has been said by benelli above, it should not be possible for you to only get 13 psi out of the thing at low boost setting. This is because 13psi is less than your wastegate actuator, and it is not normally possible to achieve that. The wastegate is the physical device with the spring in it. You can fool it to give you more boost by losing some boost on the way to it, but you cannot fool it into giving you less boost, because there is no way to do it.

On that basis, you are back to looking for changeable restrictions or your boost gauge being crap. If the boost gauge is telling you lies, then that is easy to understand. Put a known good boost gauge on it and check. If you have a restriction in your plumbing, then it would be possible for you to get 13 psi against a 14.7 psi actuator, because the turbo could be working to a 14.7 psi output pressure but then you waste some of that boost on the way to the plenum, where the gauge sees boost. That would explain both the 13 psi vs 14.7 wastegate spring and the 15 psi vs the 18 psi high boost setpoint.

mattis96 Proficient

mattis96

Posted
  • Author
Posted

Yeah it is driving me crazy. But I definitely get 13psi at lo boost, gauge tells me and dyno printout with map pressure from wolf tell me.

I might try turn boost controller off and see what happens then, don't know why I didn't try this yet.

Bought new silicone hose for vacuum and boost lines so I'll replace all that.

Jayden.K Collaborator

Jayden.K

Posted
Posted

Do actually notice the 15 to 18 psi difference because what If its going to 18 psi but your believing your faulty displays? And when it hits 18 is it a cold time of the day and when it doesn't its hot??. Your boost controller may have a faulty control solenoid

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

    • Duncan
      7 Speed Auto transmission fluid change (Skyline, Q50, Q60, Fuga, Q70, A62 Titan and probably heaps of others including Navara...)

      By Duncan · Posted

      OK, so regardless of whether you did Step 1 - Spill Step 2 - Trans pan removal Step 3 - TCM removal we are on to the clean and refill. First, have a good look at the oil pan. While you might see dirty oil and some carbony build up (I did), what you don't want to see is any metal particles on the magnets, or sparkles in the oil (thankfully not). Give it all a good clean, particularly the magnets, and put the new gasket on if you have one (or, just cross your fingers)
    • Duncan
      7 Speed Auto transmission fluid change (Skyline, Q50, Q60, Fuga, Q70, A62 Titan and probably heaps of others including Navara...)

      By Duncan · Posted

      One other thing to mention from my car before we reassemble and refill. Per that earlier diagram,   There should be 2x B length (40mm) and 6x C length (54mm). So I had incorrectly removed one extra bolt, which I assume was 40mm, but even so I have 4x B and 5x C.  Either, the factory made an assembly error (very unlikely), or someone had been in there before me. I vote for the latter because the TCM part number doesn't match my build date, I suspect the TCM was changed under warranty. This indeed led to much unbolting, rebolting, checking, measuring and swearing under the car.... In the end I left out 1x B bolt and put in a 54mm M6 bolt I already had to make sure it was all correct
    • Duncan
      7 Speed Auto transmission fluid change (Skyline, Q50, Q60, Fuga, Q70, A62 Titan and probably heaps of others including Navara...)

      By Duncan · Posted

      A couple of notes about the TCM. Firstly, it is integrated into the valve body. If you need to replace the TCM for any reason you are following the procedure above The seppos say these fail all the time. I haven't seen or heard of one on here or locally, but that doesn't mean it can't happen. Finally, Ecutek are now offering tuning for the 7 speed TCM. It is basically like ECU tuning in that you have to buy a license for the computer, and then known parameters can be reset. This is all very new and at the moment they are focussing on more aggressive gear holding in sports or sports+ mode, 2 gear launches for drag racing etc. It doesn't seem to affect shift speed like you can on some transmissions. Importantly for me, by having controllable shift points you can now raise the shift point as well as the ECU rev limit, together allowing it to rev a little higher when that is useful. In manual mode, my car shifts up automatically regardless of what I do which is good (because I don't have to worry about it) but bad (because I can't choose to rev a little higher when convenient).  TCMs can only be tuned from late 2016 onwards, and mine is apparently not one of those although the car build date was August 2016 (presumably a batch of ADM cars were done together, so this will probably be the situation for most ADM cars). No idea about JDM cars, and I'm looking into importing a later model valve body I can swap in. This is the top of my TCM A couple of numbers but no part number. Amayama can't find my specific car but it does say the following for Asia-RHD (interestingly, all out of stock....): So it looks like programable TCM are probably post September 2018 for "Asia RHD". When I read my part number out from Ecutek it was 31705-75X6D which did not match Amayama for my build date (Aug-2016)
    • Duncan
      7 Speed Auto transmission fluid change (Skyline, Q50, Q60, Fuga, Q70, A62 Titan and probably heaps of others including Navara...)

      By Duncan · Posted

      OK, Step 3, if you need to remove the valve body, either to replace it, the TCM, or to do a more complete drain.  First, you need to disconnect the TCM input wires, they are about half way up the transmission on the drivers side. One plug and the wires are out of the way, but there is also a spring clip that stops the socket from sliding back into the transmission. On my car the spring clip was easy to get, but the socket was really stuck in the o-ring of the transmission housing and took some.....persuasion. You can see both the plug to remove (first) and the spring clip (second) in this pic Incidentally, right next to the plug, you can see where the casting has allowance for a dispstick/filler which Nissan decided not to provide. there is a cap held on with a 6mm head bolt that you can remove to overfill it (AMS recommend a 1.5l overfill). Final step before the big mess, remove the speed sensor that is clipped to the valve body at the rear of the box.  Then removal of the Valve Body. For this the USDM Q50 workshop manual has a critical diagram: There are a billion bolts visible. Almost all of them do not need to be removed, just the 14 shown on the diagram. Even so, I both removed one extra, and didn't check which length bolt came from which location (more on that later....). Again it is worth undoing the 4 corners first, but leaving them a couple of turns in to hold the unit up....gravity is not your friend here and trans oil will be going everywhere. Once the corners are loose but still in remove all the other 10 bolts, then hold the valve body up with 1 hand while removing the final 4. Then, everything just comes free easily, or like in my case you start swearing because that plug is stuck in the casing. Done, the valve body and TCM are out
    • Duncan
      7 Speed Auto transmission fluid change (Skyline, Q50, Q60, Fuga, Q70, A62 Titan and probably heaps of others including Navara...)

      By Duncan · Posted

      OK, so if you are either going for the bigger fluid change or are changing the valve body which includes the Transmission Control Module (TCM), first you should have both a new gasket 31397-1XJ0A and a torque wrench that can work down to 8Nm (very low, probably a 1/4 drive one). You can probably get by without either, but I really didn't want to pull it all apart together due to a leak. First, you now need that big oil pan. The transmission pan is 450 long x 350 wide, and it will probably leak on all sides, so get ready for a mess. There are 24x 6mm headed bolts holding the pan on. I undid the 2 rear corners, then screwed those bolts back in a couple of turns to let the pan go low at that end, then removed all the middle bolts on each side. Then, undo the front corner bolts slowly while holding the pan up, and 80% of the fluid will head out the rear. From there, remove the remaining bolts and the pan is off. You can see it is still dripping oil absolutely everywhere...it dripped all night.... I got another couple of litres when I removed the pan, and then another few when I removed the valve body - all up another 4l on top of the 3 already dropped in step 1.
×
×
  • Create New...