HELP! Severe acceleration lag

juld0zer

ok, so the brake switch theory might hold some merit. Not sure if it's the brake light switch or the one which kills the cruise - more experimentation to follow.

Basically what i did was at various speeds and gradients i pressed the brake pedal enough to switch the brake lights on, then floored the gas pedal. The result is the throttle remains as it was just before the brake pedal was pressed. So acceleration is still available but at a much lower rate. It still didnt feel the same as the last few times i experienced the issue. Acceleration was still reasonably strong
Another thing i observed was that once i released the brake pedal, within a second the throttle would behave as per my gas pedal input. So if my foot was to the floor, release brake and it roars to life.

Back to the issue, i still could not replicate the dangerous lack of throttle response. I am guessing this could be because i cannot press brake and take off from a standstill at the same time (dont have 3 feet to operate all pedals) so the best i could do was feather it into 1st and get the car rolling, then brake and gas.
Once i find a safe place to test, i will disconnect brake switch and test again.

If there is an issue with brake switches on my car, i'm betting it's the cruise control one because i dont see my brake lights staying on longer than they should or spontaneously blinking. No one following me seems pissed off either, so i doubt the brake lights are blinking.
Cruise still works ok too..........

140BPM

I've been following these throttle response / lag threads for some time, and I keep seeing people mention the brake switch as a possible root cause. Though I can't seem to find a thread that covers the symptoms and fixes for it. Is it a new part replacement fix? An adjustment?

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2009 370Z Touring w/Sport 6MT

DIGItonium

Look here:
I have a serious engine problem

@juld0zer, the switch might be intermittent. I added a shimmy and it stopped working after awhile, so that's when the switch was replaced. The engine definitely sounds different when it actually opens up. It screams! Haha. At 60k miles it's definitely time to clean the intake system... just lazy.

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juld0zer

cheers for your guidance - if the switches are cheap enough i'll just replace both. let me test more first

140BPM

[QUOTE=DIGItonium;2865205]Look here:
I have a serious engine problem

Thanks a ton for this. I recently purchased my Z and it has over 60k miles on it, and throttle response/lag is very random but becoming bothersome. Most likely needs to be inspected anyway.

On a side note, while reading all these hesitation/loss of power posts, I have been keeping track of everyones reported oil temps - most seem to be 200 or lower during normal driving. Seriously? It's been upper 80s and humid here in PA lately and I'm at 220 while driving very cautiously. If I get on it even briefly I'm up between 230-240 almost instantly. From what I understand limp mode isnt until the 260-270 range, but does it seem normal for my oil temps to be consistently that high?

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2009 370Z Touring w/Sport 6MT

juld0zer

09 model doesnt come with the factory oil cooler so that can be a factor. until you start getting live data from your engine's sensors it's hard to pinpoint the cause

juld0zer

Ok, so i finally had some time to do some experiments - because driving around with no brake lights or brake lights constantly on is not cool. In short, i was eventually able to replicate the problem/induce it.

The system is more complex than one would expect, so i don't understand why Nissan chooses to do it this way on all their cars. My gf's Mazda2 makes do with just one switch assembly which activates the brake lights, cuts the cruise control and frees the gear selector.

If you press the brake pedal while accelerating, you will NOT be able to open the throttle any further than the position it was in the moment you pressed the brake pedal. When you let go of the brake pedal, the motor will roar back to life and accelerate as it should. Sort of feels like brake boosting in a way. This is supposed to be a safety feature, preventing you from accelerating while braking.

The brake lamp switch is a normally CLOSED switch. Ie. continuity only exists when the pedal is pressed.
The ASCD (cruise control) switch is a normally OPEN switch. ie. no continuity when the pedal is pressed.
These two switches act like an interlock, as described on page EC-505 of the FSM.
Therefore, disconnecting both switches or one at a time will not induce the problem.

To induce the super-lag, i had to simulate a depressed pedal. I did not want the brakes to interfere with my experiment as we all know the brakes can easily slow down the car. I already knew that pressing the brake pedal even lightly while accelerating will not allow me to go any faster, even with my foot to the floor.

To simulate a depressed pedal, i disconnected the ASCD switch and used a jumper wire across the terminals of the brake light switch connector (loom side). This is the point where i blew 2 fuses because the jumper wire shorted to ground. OOPS! Be careful

With this set up, i was able to induce the lag and learn a little more.
I could not get the throttle to open up more than 18 degrees. Test conditions were similar to the night i created the logs.

It seems that once the ECU realises you've been trying to accelerate while braking for a certain period of time (or distance?), it will switch to this limp mode where the throttle plates open extremely slowly and only to a narrow angle/range. I realised this when i removed the jumper wire and reconnected the brake light switch. Brake lights worked as they should (when jumpered, the brake lights were constantly on), but i could not escape this limp mode. The ECU at this point must be thinking the car is in a runaway situation. This explains why the problem vanishes after the engine is shut down and restarted.

Now, as i've outlined above, having one faulty switch shouldn't cause the problem. Bizarre? I think so.
Being electronic, i wouldn't rule out both switches failing at the same time as they are used equally as often as each other. My theory is that the rubber blobs on the pedal assembly could be worn out or causing the switches to stick in their respective pedal down positions or some gunk has accumulated inside the switches.

DIGItonium

The other day I accelerated at WOT in 2nd from 1.5k RPM because the car wouldn't scoot at the light. It took forever for it to reach redline. Even if it did, the engine wasn't screaming even at redline. It felt like a 3rd to 6th shift at low speed. I am starting to feel a bit of "roughness" as if he car isn't sure if it wants to accelerate or let go while the foot is planted, so it's pretty rough getting in gear. Plus, it feels like the motor briefly shuts off in between shifts as it bogs. The entire weekend I couldn't get anything close to 7-9 PSI. In fact, the car barely hit 5 PSI at full throttle in 2nd gear and it's obvious the throttle wasn't fully open. You're right. Back then when I had this issue I had to shut the car down, wait a bit before starting, and the "problem" went away.

Too we can't apply throttle with skill without the nanny ware kicking in. Looks like it's time to get it checked again.

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juld0zer

disconnect the brake light switch and give it a go. do it in a quiet area though. it's the right side one with a chunky connector (white)

esfourteen

I plan on cutting the brake light signal to the ECU and disabling the DTC via uprev, I'll report back if it actually fixes things for me, if not at least I can do some fun burnouts

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juld0zer

next time it happens to me, i'm going to disconnect the brake light switch & see what happens. oh wait... that's futile.....

juld0zer

the problem is becoming more frequent for me. i will either adjust the brake light switch or change that rubber stopper for a stiffer object

tjlazer

I wonder if anything can be done with a tune to disable this brake check sensor, etc...

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2009 370Z Monterey Blue,Nismo Conversion,RE-11's, K&N Typhoon intakes,Blue Kickplates,Homelink,FI 18" CBE,ERZ HFCs,Hotchkis sways, Swift Spec-R, EVO-R Highwing, UPREV

juld0zer

i believe disabling ETC via uprev might do just that. except you'd lose features like SRM etc

juld0zer

ok so the issue became so frequent and random that i deemed the car unsafe to drive. i ended up doing a dodgy fix to keep me going until i have more time to investigate it further.
the fix is simply a paperclip jammed into the harness side connector, simulating the brake pedal at rest position (ie. closed circuit).

works a treat and it's a cheap troubleshooting trick for anyone suspecting a faulty/incorrectly adjusted brake pedal sensor