Nissan 370Z Forum - View Single Post - New thoughts on "Ice Mode" & possible solution?

SonicVQ · 08-06-2021, 11:32 AM

Over the years, there has been a lot of talk and worry about "ice mode".
I don't know why, but I find this topic very interesting...

After reading this thread Lock up and ice mode I started to dig into what could be going on...

From what I have read, the common item is sudden hard braking after a straight and if you get off and then back on the brakes, it is back to normal.
That got me thinking about brake booster vacuum. Low vacuum = low brake boost = very little brakes.

When the VVEL is controlling the air intake to the engine (typically during light-mid engine load) the intake manifold has very little vacuum of about 4 in/Hg (data logged via OBD)

Also, when the VVEL system is controlling the air intake to the engine, if you lift off the accelerator pedal, the throttle bodies quickly close have vacuum for the brakes. It is like a quick "recharge"

Because of this, our brake booster has its own pressure sensor. This is used to make sure there is a specific amount of vacuum in the booster. If it gets low, the throttle plates close for a moment to "recharge" the booster.

However, during wide open throttle, there is almost no intake vacuum.

What if the brake booster or check valve in the brake booster hose has a slight leak, allowing the booster to loose the stored vacuum while going WOT down the straight?

Then add a very quick transition from WOT to brake, where booster vacuum may be low and if your transition from WOT to brake is quicker than the time it takes for the ECU to close the throttle and create vacuum, you won't have much brake boost or vacuum and little brake function.

People have said that when it happens to them, if they get off the brakes and back on, full braking is restored... I wonder if that slight bit of extra time, allowes brake booster vacuum to build up?

So, how to test this theory?
I have two thoughts:

• Since the brake booster pressure sensor's voltage is available through enhanced ECU diagnostics (OBDLink or OBDFusion with $14 enhanced add on) the voltage can be easily data logged and monitored.

• Add in an electric vacuum pump to the brake booster before the check valve.

So, that's my thought/theory.
What do you think?

08-06-2021, 11:32 AM	#1 (permalink)
SonicVQ Base Member Join Date: Jan 2016 Location: Ontario Posts: 230 Drives: G37 Sport Rep Power: 6721	New thoughts on "Ice Mode" & possible solution? (Nope!) Over the years, there has been a lot of talk and worry about "ice mode". I don't know why, but I find this topic very interesting... After reading this thread Lock up and ice mode I started to dig into what could be going on... From what I have read, the common item is sudden hard braking after a straight and if you get off and then back on the brakes, it is back to normal. That got me thinking about brake booster vacuum. Low vacuum = low brake boost = very little brakes. When the VVEL is controlling the air intake to the engine (typically during light-mid engine load) the intake manifold has very little vacuum of about 4 in/Hg (data logged via OBD) Also, when the VVEL system is controlling the air intake to the engine, if you lift off the accelerator pedal, the throttle bodies quickly close have vacuum for the brakes. It is like a quick "recharge" Because of this, our brake booster has its own pressure sensor. This is used to make sure there is a specific amount of vacuum in the booster. If it gets low, the throttle plates close for a moment to "recharge" the booster. However, during wide open throttle, there is almost no intake vacuum. What if the brake booster or check valve in the brake booster hose has a slight leak, allowing the booster to loose the stored vacuum while going WOT down the straight? Then add a very quick transition from WOT to brake, where booster vacuum may be low and if your transition from WOT to brake is quicker than the time it takes for the ECU to close the throttle and create vacuum, you won't have much brake boost or vacuum and little brake function. People have said that when it happens to them, if they get off the brakes and back on, full braking is restored... I wonder if that slight bit of extra time, allowes brake booster vacuum to build up? So, how to test this theory? I have two thoughts: • Since the brake booster pressure sensor's voltage is available through enhanced ECU diagnostics (OBDLink or OBDFusion with $14 enhanced add on) the voltage can be easily data logged and monitored. • Add in an electric vacuum pump to the brake booster before the check valve. So, that's my thought/theory. What do you think? Last edited by SonicVQ; 08-07-2021 at 12:53 PM.