ANXIOUZ

iTrader: (13)

All of the people I know with Z's that have spun out and had damage have been experienced guys who turned off TCS for more fun. Base model or not, you just need to know when to be prudent. For example, sharp cloverleaf turn in the rain at high speed...not prudent.

MustGoFastR

iTrader: (13)

Correct. The way to accomplish this without doing a massive burnout until the SLIP light comes on and stays is by installing the switch that I mentioned.

Spike100

Now I am confused about at least the VDC function. I get the TC function: Apply too much power, and TC kicks in and kills that excessive power (hopefully before you lose the rear-end grip and start spinning like a top). But, what does VDC do?

I have a 2003 Performance model (which has VDC). I’m in Minnesota where we have ice on the road for about 4 months. I have never driven my Z in winter until this year (so far this winter has not been typical in Minnesota; it was 40 degrees today). Since we have not seen much snow this year, I am still driving the Z. Life is good. I have summer performance tires (not a good idea in winter) so I am doing the occasional slide. With VDC on (of course I always leave it on in winter), and when I make a mistake (like I did a couple of days ago, jumping on the accelerator doing a left turn in front of traffic), VDC works great keeping the car going straight with just a little bit of drifting on the ice.

I read your posts (about how VDC does not turn off completely) and decided to do a test. I went to an empty parking lot that had some ice.

TEST 1 – VDC (on)
Action: Accelerate to about 30mph, turn hard left on the ice while accelerating.
Result: TC (or I guess VDC since I have the Performance model) kicks in, power kicks off, car slides to the side (drifts), car straightens itself. Reapplying power sends the car back into a straight line without adjusting any steering. VDC obviously works pretty well.

TEST 2 – VDC (off) (i.e., one press on the VDC button)
Action: Accelerate to about 30mph, turn hard left on the ice while accelerating.
Result: Whoa baby: Back-end loses grip, and car slides around like a top (total loss of direction and control; that would be a spin-out).
----------------
Analysis: If there was any part or feature of VDC that was operational on Test 2 (with VDC turned off by pressing the VDC button), it was not apparent. In Test 2 the car “lost-it.”

Discussion:
1) Maybe it is simple TC that saved me on ice since TC cut power. I have no way of knowing what part or function-extension VDC did here.
2) My test, run on ice at slow speed, may not be a valid comparison to a high-speed test done on a track. There is no way I’m trying this test at higher speed on a dry surface. I’m not enough of driver to do this. But, maybe someone else has done this and can report the result.

I would like to know if you can turn VDC off. I thought you could, but maybe not?

--Spike

MustGoFastR

iTrader: (13)

You basically answered all you own questions. As far as VDC compared to TCS in your tests, in test 1, the car would have spun out; TCS can stop the rear wheels from spining, but not the car itself in a turn. The individual wheel braking in addition to the YCS, which is VDC is what straightened you back out and kept the car on it's intended path.

In test 2, you are correct, VDC was off and did not interfere. Where it HAS been shown to interfere even when in the off position is not while accelerating around a curve, but when you BRAKE going into a curve or in the middle of it. You didn't do this; that's why you saw no interference from it.

"I would like to know if you can turn VDC off. I thought you could, but maybe not?"

I don't get why you are asking this. By your own account, you turned off your VDC and by your test it appeared for all intents and purposes to be off, so why would you be thinking this way? At any rate, to cut it off completely, you can either put a switch inline with the power wire to the yaw sensor or hit the button and do some donuts until the SLIP light comes on and stays on along with the VDC OFF light and will not go out regardless of what you do with the button until you restart the car.

Spike100

re: "I don't get why you are asking this."

Hello... because you are saying: "At any rate, to cut it off completely, you can either put a switch inline with the power wire to the yaw sensor or hit the button and do some donuts until the SLIP light comes on and stays on along with the VDC OFF light and will not go out regardless of what you do with the button until you restart the car."

...Which means to me that you are saying simply pressing the VDC switch won't completely turn-off VDC.

Did I get this right?

--Spike

Kolia

iTrader: (2)

The « Is the VDC off is 100%? » argument has been going on for a while. We haven’t agreed on that yet. My opinion, which seems to be backed by Nissan literature, is that the VDC is fully OFF once the button is depressed.

The thing is, there are still plenty of other electronic systems still active even after the VDC is OFF, like ABS, EBD and ABLS. That last one will affect the car’s behavior as it acts as a secondary differential lock.

Your test showed what the VDC does. It selectively applies brake pressure to individual wheels to correct the car’s trajectory. It compares the steering angle (where YOU want to go) with data from the yaw and G sensors (where the car IS going) and decides what corrective measures to take. Brake to outside front wheel to correct oversteer, brake on inner rear wheel to correct understeer. These measures will almost always include a signal to the TCS system to cut power. TCS affects the throttle, possibly ignition too.

The main argument guys have that VDC is not off, is that they can do big burnouts/donuts and eventually SLIP and VDC OFF lights turn ON and it becomes easier to do new burnouts/donuts. My opinion is they just got the ABLS (Active Brake Limited Slip) system to freak out because it couldn’t control the rear wheels’ different speeds without extreme brake application. Instead of burning up the brakes and stressing the drive train, it shuts off. It’s now easier to do burnout because you’re basically spinning only one wheel. This by the way works wonder on the temperature sensitive VLSD. These guys are blowing their diff doing that…

My 2 cents.

ANXIOUZ

iTrader: (13)

You guys raise interesting points but I'm a simple man and so are my theories.

I believe VDC does turn completely off. I just think the sensors remain on with the ECU just not "correcting" things. I think the ECU still recognizes quirky sensor data and when things get crazy it might cause SLIP lights and the other "hey is my VDC on?" things to happen.

I have no proof or anec-dotal evidence. Just speculation based on my own experiences.

Fletch69z

iTrader: (50)

VDC does not fully disengage unless you shut off the power to the unit.

MustGoFastR

iTrader: (13)

Can you explain this more completely?


Not sure I agree with the rest of your reasoning. It makes sense in the terms you describe it (low speed burnouts, donuts and such), but I've seen accounts of VDC interfering (when "off") of people coming into corners and braking into the turn. ABLS only functions at speeds up to 20MPH, IIRC, so it would not be the source of the interference in the situation I described.

Isn't it redundant (and thus basically stupid) for ABLS to be active on any car other than the base model? If you've got a mechanical LSD (viscous or otherwise), what purpose does ABLS serve?

Kolia

iTrader: (2)

I've never heard anything about a 20mph limit to the ABLS. Where did you get that info? I'm not flamming, just asking.

Yeah, braking hard into a turn is prone to set the ABS off. Killing speed and often inducing crazy understeer. That's to be expected and not the action of the VDC. The VDC would actually help to get the car turning...

ohSIXz

first thing i do after turning the car on is turning TCS off. i have an enthusiast, so no vdc.. i thought i remember a thread like... a year ago about disabling vdc completely. if u take off the shift boot there is a wire connected to a "bosch" unit, if u cut the wire you will never have vdc again. that is if i remember correctly.

when tcs is off, its off.

MustGoFastR

iTrader: (13)

It's been a while, but I either read it in the service manual or the car's manual back when I was trying to figure out what the heck it was. If I get bored this weekend, I'll try to find it.

As for the ABS, that's pretty easy to recognize when it's doing it's thing; I'd think the people saying it was VDC would be able to tell the difference, but who knows?

MustGoFastR

iTrader: (13)

Or just put a switch in-line with the power wire to the unit like I have.

Kolia

iTrader: (2)

I'll check on my side.

Frankly, the simple fact that people experience the VDC problem under braking tells me It's probably not the VDC. The chances that it's the ABS, or something else, like I discribed is much more probable.

Plus, by definition, if the VDC was active, any form of hard counter steering would set it off. I've never had any form of brake activation while spinning out, dispite my best efforts to steer in the spin. Try it, you'll stop at 180 degres when the engine stalls... Silly understeer on full lock woud also set it off.

Spike100

Exactly. I did go back to my "test site" tonight, and ran the same tests I did and posted about earlier here except this time I did the test with no-power-on and no braking, and did it again with no-power-on and with braking. Both tests with VDC ON and OFF. In these tests TC never happens (of course), VDC when OFF never seems to do anything, but touching the brakes always activates ABS when sliding (VDC ON or OFF). --Spike

MustGoFastR

iTrader: (13)

Hmm, I've been digging around the service manual and haven't been able to find a thing on ABLS; no mention of it whatsoever, despite notations I've found elsewhere on the web of it being one of the VDC related functions.

I did find this:
That's what happens when you do a crazy burnout or something after turning VDC off. I guess if ABLS was a function of VDC that remained active when VDC is off, it could have something to do with all this; you still can get the slip light to flash even with VDC off, so maybe it is the ABLS kicking in at that time and if you completely defeat the system by making the slip light come on and stay on, then ABLS is deacivated?

Odd, though, that I cannot seem to find ABLS in the manual...

Kolia

iTrader: (2)

References to ABLS is pretty hard to find! I'm still looking...

I did find this in section Brake Control System (BRC) page 87 of the 2005 Technical Manual:

At least that is in line with our findings!

Kolia

iTrader: (2)

The only reference to the ABLS I've found so far is from the owner manual.

Page 5-23 of the 2006 Manual, Starting and Driving

MustGoFastR

iTrader: (13)

Hmm, well, given that info., then it IS most likely the ABLS that people are feeling intervene even with VDC off, so throwing the car into the VDC failsafe mode by sliding around like crazy or putting in a switch is th ticket to getting rid of that as well. Aslo, this, then answeres the question that VDC is NOT completely off when you hit the button, as ABLS is a function of VDC and remains active when the button is pressed.

I don't know where, then, I saw the reference about it only being active up to 20 MPH... damn odd, too, that there seems to be no reference to it in the service manual.

Still, from the description of the operation of this system, I don't understand the purpose of it being present on a car that has a mechanical LSD, since it's the LSD's job to do exactly what ABLS says it does.

Kolia

iTrader: (2)

We're getting into sementics here. But if we look at the definition of what each systems are designed to do, we'll find that the VDC is there to change the car's direction relative to the steering input. That part of the electronic package is completely turned OFF when we hit the VDC button.

I think people are confusing VDC OFF with an imaginary "All electronic OFF" button and thus have the wrong expectations.

For the ABLS + VLSD thing, I'm not a drivetrain designer but I know that visous lock LSD can't be 100% lock ever. The lock ratio is a function of the temperature of the viscous fluid. The hotter, the ticker it gets. It get warmed up by a speed differential between the left and right wheel. So as soon as they both spin at the same speed, lock is released and one wheels can go free spinning again.

The ABLS will be able to assist the VLSD (which would have a hard time locking at low speed, might be the 20mph you've found) to make sure the wheel speed is kept equal. I suspect the ABLS will also be aware of the car's attitude so it doesn't try to lock the diff in a sharp corner. So it's still getting data from the yaw and steering sensor as long as it's active.

Why add the ABLS to the VLSD in the first place ? Pricing I guess. The diff is a cheap one to get and all the electronic hardware for the ABLS is present with the VDC package. So it's "free".