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Midrange Flat Spot...

25GTV

By 25GTV,
in Engines & Forced Induction

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  • 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?

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