Jump to content
SAU Community

Midrange Flat Spot...

25GTV

By 25GTV,
in Engines & Forced Induction

 Share

Recommended Posts

  • 2 weeks later...
666DAN Grand Master

666DAN

Posted
Posted
The variable length manifold could be sticking....

+1

Has someone recently fitted a pod filter to the car and just blocked the line that runs from the control solenoid on the butterfly valve? (actuator between the dual entry)

This line must go to the intake as when it opens it needs flowing air, blocking it prevents the butterfly from opening up.

Most people accidentally do that when they remove the air box, as that's where the line goes, they just plug it...big no-no and loses you massive amounts of power.

N-DAWG Mentor

N-DAWG

Posted
Posted

hmmm interesting reading this as since having my turbo conversion done i've been noticing a flat spot in the mid range. Sometimes I'll be around 2-3k revs in 2nd or 3rd (tiptronic auto) and WOT just sort of struggles? It's like it wants to up n go but can't until it gets to around 4-5k. I thought maybe it's just the characteristics of this set up, or just the auto transmission isn't getting the power down well enough in the mid-range.

Now I just thought this valve was controlled electronically based on revs, didn't realise it was controlled by vacuum lines. Since reading this thread I've decided to check the online R34 workshop manual http://www.scribd.com/doc/5332929/Nissan-S...-Manual-English to see how the vacuum lines run.

On page 15 of the navigation on that link, I followed the vacuum lines from the canister to where it meets the first hard line, and also done the same for the airbox vacuum line, and then compared it to how it is on my car. The result is that they're switched around at the first pair of hard lines. Basically what appears to be the hard line that leads to the variable intake solenoid is getting a vacuum signal from where the airbox used to be. The line isn't plugged though just tucked away.

Now it seems to me that this seems to be the reason I'm having a midrange flat spot. Could be the same case for the OP?

Would there any reason why my vacuum lines are being run this way or is it more than likely human error in reconnecting them? More to the point, given that it's been tuned the way it is, would reconnecting the vacuum lines to match what is in the workshop manual cause me any issues with the tune?

iseekool Veteran

iseekool

Posted
Posted
think this is the problem i mioght have..r33 n/a auto...

happens usually around 60km/hr i notice tho struggles and slows for a bit then goes back to normal

anyone show pics on what to do/ to fix?

thanks

I'm assuming you are on light throttle? If that is the case - it is due to the car being too high in gear (4th) and the torque converter locking - to help save fuel.

The reason the the car then feels "normal" afterward is because the ECU/TCU detects the engine is "struggling" so to speak, therefore it releases the tourque converter lock and lets the trans slip in 4th or will down shift to 3rd.

Do you feel the engine has problems reving up smoothly?

_bobo_ Mentor

_bobo_

Posted
Posted
I'm assuming you are on light throttle? If that is the case - it is due to the car being too high in gear (4th) and the torque converter locking - to help save fuel.

The reason the the car then feels "normal" afterward is because the ECU/TCU detects the engine is "struggling" so to speak, therefore it releases the tourque converter lock and lets the trans slip in 4th or will down shift to 3rd.

Do you feel the engine has problems reving up smoothly?

Usually not full throttle medium-had throttle it sometimes happens, speed just dies down a bit then goes bak up( not when changing gears but while its revving through out it)..and not usually in a high gear but say if i use 1 2 D on gear shift.

666DAN Grand Master

666DAN

Posted
Posted

Kinda right, it is triggered by the output from the ECU, it uses the same pin as the GTt which triggers the boost solenoid from low to hi boost.

In the 25GT it controls the actuator for opening up the intake, but when it actuates it pulls air through that hose. If the hose is blocked it forms a vacuum sucking against nothing, so doesn't open up. That hose needs to go to atmospheric for the actuator to fully function.

so you need two things

-Signal from the ECU telling it to open (can wire 12v directly to it and it's open 24/7)

-hose going to air intake, no obstruction so the valve can open, on a turbo car pick it up from the pressure side.

hmmm interesting reading this as since having my turbo conversion done i've been noticing a flat spot in the mid range. Sometimes I'll be around 2-3k revs in 2nd or 3rd (tiptronic auto) and WOT just sort of struggles? It's like it wants to up n go but can't until it gets to around 4-5k. I thought maybe it's just the characteristics of this set up, or just the auto transmission isn't getting the power down well enough in the mid-range.

Now I just thought this valve was controlled electronically based on revs, didn't realise it was controlled by vacuum lines. Since reading this thread I've decided to check the online R34 workshop manual http://www.scribd.com/doc/5332929/Nissan-S...-Manual-English to see how the vacuum lines run.

On page 15 of the navigation on that link, I followed the vacuum lines from the canister to where it meets the first hard line, and also done the same for the airbox vacuum line, and then compared it to how it is on my car. The result is that they're switched around at the first pair of hard lines. Basically what appears to be the hard line that leads to the variable intake solenoid is getting a vacuum signal from where the airbox used to be. The line isn't plugged though just tucked away.

Now it seems to me that this seems to be the reason I'm having a midrange flat spot. Could be the same case for the OP?

Would there any reason why my vacuum lines are being run this way or is it more than likely human error in reconnecting them? More to the point, given that it's been tuned the way it is, would reconnecting the vacuum lines to match what is in the workshop manual cause me any issues with the tune?

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

    • davemoto63
      My new to me M35 Stagea wagon

      By davemoto63 · Posted

    • davemoto63
      My new to me M35 Stagea wagon

      By davemoto63 · Posted

      Just bought a 2002 Stagea 250tRS VR-X Four AERO VQ25DET and spent the last two weekends cleaning and detailing it.. still have to do the wheels and the engine bay but the rest of it came up nice. Imported 2011 to S.A. and I'm the third owner since it was imported. I met the guy who brought it over, he went to Japan and picked out the car, bought it and ordered the wheels. He also gave me a list of stuff he did to the car with receipts. Coil overs (I have the original springs), 3" exhaust from the dump pipe back no cat, Custom dump pipe,(I have the original exhaust), Plenum spacer, 18" custom Work XSA wheels (need restoring, I've made a start..), Shift kit put through the 5 speed tiptronic auto, TV and menus/screens changed to english, Australian DTV tuner installed in rear. I've just had four new discs and new pads as well as all the fluids including the brake fluid replaced. I have all the receipts for the last 15 years and the import papers in a nice folder. Car looks great, goes like hell but fuel economy is not a thing lol.. pics next..
    • silviaz
      Steps to DIY sanding car back ready for respray....

      By silviaz · Posted

      I ended up in this rut again lol, and used a shit ton of filler. One thing I can't understand is, even after using a big long block and going in long X pattern strokes, I always end up at bare metal again with no filler, and my repair started at one end of the door and now I've chased my tail to almost the other end of the door. I was thinking of hitting the panel with a hammer where it might be a high spot and making everything low then filling it, I did this on a small section on my other door by mistake and I think I fixed it lol. Is this a bad idea? The other thing is with guidecoat, whether it's the powder or spray, after I sand all the guide coat off, it doesn't reveal anything for me in terms of high spots and low spots and makes it especially hard when it's bare metal (at least in powdered form), am I doing something wrong here, or likely a high spot I keep going over and creating valleys? Lastly, stupid question but, is it possible that after sanding if I only sand over the filler area where I know to be a dent that it's impossible for me to dig into that dent? Unless there are other problems which I missed.  
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      Yeah the rule of thumb with an LS is 7psi per 1000rpm. That is decidedly not enough at 6800rpm. I mainly looked for the scenarios where knock started to be picked up and it was later in the session when things were hotter, and oil was thinner, and the pressure was lower than it should be. (i.e very horrible). I am hoping with thicker oil (I was running Penrite ten tenths 10-40, the manual specifies 10-30) that does not leak that it's much improved at that time!!! I am using Project Mu Club Racer CR pads. I'm also using the Project Mu 335C fluid. The symptoms imply that it was fluid that boiled, but no bubbles seemed pretty weird to me when I bled it today. I want to try Castrol SRF as it has a much higher wet temp but, well, I have new Project Mu fluid lol... so I should at least use that. The pedal on track was really noticable. It went from basically normal feeling to instantly near-floor. The car did pull up as before, it was just very much nearly at the floor before the brakes engaged. At that point I pretty much decided the day was very done, it did *kinda* come back during that very slow cooldown lap into the pits. Felt perfectly fine driving home.
    • fatz
      Beers and skylines Fatz style

      By fatz · Posted

      f**king around with the bro
×
×
  • Create New...