VTC question

[Tom N]

Looking to double check something before I do a bunch of work for nothing. I believe me VTC sprocket is bad. I have a S15 motor that started to make a loud rattle/tapping noise at idle. Only does it at idle. My searching has lead me to believe it is VTC related. I have removed the solenoid and applied 12v to it and moves the plunger in and out. With the solenoid back in the head and the plug removed I applied 12v to it and I can hear it ticking as it pushes the plunger in and out but my idle does not alter or get lumpy not does the Taylor/tapping noise change. Would it be safe to assume at this point that its the the VTC sprocket gear that is bad and needs replaced.

[jr_ss]

I believe the cam gear is only active when the ECU sees a change of state in the TPS value(just off idle) and 5200. I cant give you specifics on it because I do not have access to my FSM. Below the activation point(just off idle) it will not change idle. If the noise goes away upon rev and/or once the motor is warm, it's the gear and not the solenoid. It's common on higher mileage motors and with upgraded cams/springs.

[rwtf]

i seriously always wondered wtf the vtc actually does...

[oni jake]

Serious question?

It advances timing on the intake cam. It gives the SR a significant boost in low-end torque.

[s14_mike]

Change the vtc sprocket. I had the same problem as the one that you are explaining. It's common and the sprocket gets worn out over time.

[Tom N]

I believe the cam gear is only active between 1700 and 5100. I csnt give you specifics on it because I do not have access to my FSM. Below the activation point(1700) it will not change idle. If the noise goes away upon rev and/or once the motor is warm, it's the gear and not the solenoid. It's common on higher mileage motors and with upgraded cams/springs.


But from what I can tell through reading if I pull the plug on top of the VTC solenoid and supply 12v power to the solenoid then it should cause it to activate the VTC and which will in turn cause the idle to get real lumpy like a car with a real aggressive cam would sound. This doesn't happen though. When I supply 12v power to the solenoid I can here the solenoid click but no change in idle.

[jr_ss]

But from what I can tell through reading if I pull the plug on top of the VTC solenoid and supply 12v power to the solenoid then it should cause it to activate the VTC and which will in turn cause the idle to get real lumpy like a car with a real aggressive cam would sound. This doesn't happen though. When I supply 12v power to the solenoid I can here the solenoid click but no change in idle.

Tom, do you have the FSM? I'll be home Thursday as stated and I can give you more solid answers on your questions.

[Tom N]

Tom, do you have the FSM? I'll be home Thursday as stated and I can give you more solid answers on your questions.

I have a digital copy of the FSM.

[DET240SX]

Hi Tom,
Did you ever fix this issue? I'm might be having the same problem. At idle my motor makes the clicking noise periodically. I haven't checked minor ground locaitons but it lead me to believe the VTC solenoid based on this thread and Headup240's build thread. Pls let me know - thanks!

[Tom N]

Hi Tom,
Did you ever fix this issue? I'm might be having the same problem. At idle my motor makes the clicking noise periodically. I haven't checked minor ground locaitons but it lead me to believe the VTC solenoid based on this thread and Headup240's build thread. Pls let me know - thanks!

It was the VTC cam gear. Not the solenoid.
The solenoid is easy to check though. Just put power and ground to it and it should click.

[Tom N]

i seriously always wondered wtf the vtc actually does...
http://www.glpp.info/hu6j.jpg

It gives you more low end power with out sacrificing top end.

[jr_ss]

It retards/advances(+/- 20*) intake cam timing to increase lowend power...

[Kingtal0n]

On my S15 the solenoid would make an audible "click" whenever you pressed the gas pedal (moved the TPS) even slightly at idle. That tells me that the VTC was disabled at idle, but enabled once you hit the gas, and re-disabled at 5200RPM while at wide open throttle.

IIRC there was some kind of FSB involving the VTC on early s15 engines.

And I believe the reason they leave it disabled at idle is due to oil pressure. If there is no enough oil pressure and you activate the solenoid to move the camshaft, it could slop around and potentially starve other components in the head.

[jr_ss]

It is enabled just off idle, when the ECU sense a change of state in the TPS value.

[Kingtal0n]

It is enabled at 1700-1800rpms.

I know what "they say" but you must be aware not all engines and ecu are created equally. When I installed a PFC to the S15 engine, I had the ability to adjust the on/off point of the VTC. By playing with that setting, I verified that the VTC would come on at 900rpm when you touched the gas because it would make an audible click. I did this by essentially turning the VTC off at 500rpm (always off). The solenoid would refuse to click, indicating that it was no longer advancing the camshaft.

[jr_ss]

So just to clear this thread up of misinformation, I spoke with Martin(R.S. Enthalpy) about the engagement points.

"VTC should engage once the ECU recognizes a change of state in the TPS value. Once engaged, it operates up to 5200rpms."

So it's safe to say I was previously misled and I'm glad to get the correct information in this thread for those of you that care.

Kinglaton, those set points in your PFC should be accurate, however most factory ECUs configured around the same engine/setup contain the same algorithms and shouldn't vary much. Obviously there is a variance, but not a 900rpm one.

[dorkidori_s13]

i seriously always wondered wtf the vtc actually does...

from my understanding, since the OEM SR is SOOOO prone to boost lag (any redtop owner will know what i am referring to), nissan integrated VTC on the intake cam to help with low end torque and the boost lag feeling. especially since they upped the boost a bit and utilized a much larger T28 (over the S13s itty bitty T25) on the S14/S15 motors.

[Kingtal0n]

"VTC should engage once the ECU recognizes a change of state in the TPS value. Once engaged, it operates up to 5200rpms."


Kinglaton, those set points in your PFC should be accurate, however most factory ECUs configured around the same engine/setup contain the same algorithms and shouldn't vary much. Obviously there is a variance, but not a 900rpm one.

How is that different from what I said?


On my S15 the solenoid would make an audible "click" whenever you pressed the gas pedal (moved the TPS)

[jr_ss]

How is that different from what I said?

Do you have problems understanding things? I confirmed what you stated, that is all.

[Kingtal0n]

Do you have problems understanding things? I confirmed what you stated, that is all.

No, you said something about an algorithm and a 900 rpm "variance". There is no algorithm, and 900rpm was the idle speed of that car not a variance.

[jr_ss]

Perhaps you should go back and reread what I wrote...