HELP! Severe acceleration lag

juld0zer

hey guys, what are your thoughts on the possibility of VDC interfering due to a slight difference in tyre wear (rears naturally being slightly more worn than the fronts)?

I switched VDC off via the button when i last experienced this lag but it didn't make any difference.

The thing that stands out most to me is the huge difference in accelerator pedal voltage vs throttle body voltage.

During lag: 4.66v pedal vs 1.03v throttle.
Normal: 2.01v pedal vs 1.13v throttle.
These figures are taken from logs where vehicle speed and acceleration requirement was similar - ie. taking off from a stand still in 1st gear, 10mph, similar rpm, afr and mass air flow. I assume 4.66v is pretty much foot to the floor so it clearly shows a huge lack of correlation between the pedal and throttle.

Intake cam solenoid duty % were similar for both logs.
However, "INT/V TIM(B1) (Deg CA)" shows another huge difference.
During lag: 7 deg CA
Normal: 49 deg CA.
(nb: just specifying Bank 1 readings for simplicity, bank 2 readings were different but similar)

Dud cam angle sensor? Dud throttle position sensor?? Or a false failsafe trigger. Whatever it is, there is no CEL or error codes

DIGItonium

You can still hit redline, right?

Can you blip the throttle past 2k RPM and then get the car rolling in 1st like normal? I hate how the throttle fully won't open up under 2k RPM causing the surge in power after 2k RPM after nearly stalling.

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juld0zer

yep, but it just takes forever to get to redline. getting up to 60kmh takes a lot of effort and gearbox rowing.

Yep, i can take off at any revs (i actually have to ride the clutch for a while with the revs above 2000 to avoid stalling when this happens) but i cant feather to clutch without touching the gas pedal - let's say like backing out lf a carpark spot. It literally feels like i am driving an old hatchback.

Surge is a good way to describe it when the revs reach about 2000. It's not a smooth drive.

I thought you fixed your problem?

Plasmite

Glad to know this is "normal"

I always attributed that to the fact I always leave VDC on

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WISHLIST

juld0zer

it's not normal mate. what you are experiencing is probably heat related. Something along the lines of heatsoak or warm intake air temperatures. That will easily cause a lag on take off that feels more like nothing is happening for a second or 2, then the engine roars to life.

i drive with VDC on 98% of the time too.

another way i can describe my issue is to imagine your gas pedal has been remapped to only open the throttle plate up to 1/4 of its full range. so foot to the floor = 25% throttle. halfway = 12.5%... painful. Scary when merging into traffic - esp if you expect normal acceleration but get nothing.

Page EC-481 of the fsm describes this as being the cause for P1805 (brake switch fault) : "A brake switch signal is not sent to ECM for ex- tremely long time while the vehicle is being driv- en."
This supports the highway driving situations where some people have experienced this problem. but i've had it happen to me while driving in urban areas where there are a lot of turns, traffic, speed bumps etc - basically lots of brake use

DIGItonium

Mine's not a temperature problem, but more of a the tune that came with the kit. I've decided to leave it alone for now since it's driving fine.

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juld0zer

but when you had a faulty brake switch, you had the same problem as i have ay? except yours seemed constant but mine comes on randomly and stays on when it does.

have you tried the 2300 curve? or do you only have the basic Uprev license?

cheshirecat

IMO, this sounds like the tune. Throw the stock tune on and see if the issue persists. This is beyond problems caused by temperature. I would have also indicated the brake switch as a possible condition but that seems to be ruled out.

DIGItonium

I don't have the tuner license, and I can't quite justify $700 for a tuning session at the moment (60k on the motor). That doesn't include the mini road trip to a shop in TX either.

The brake switch issue definitely resolved the power cut issues I had when the car was bone stock. The car literally stalled under 2k for a couple of seconds while making a left turn! I've even floored it in 1st and 2nd while making the turn. There were issues where I could feel power cutting at each 1k intervals to redline, and the tech thought it was fuel cut. The engine is fine, but the throttle wouldn't open up. Once I had the issue remedied, the car sounded different. The motor sounded different, and it hauled angrily to redline and even spun the tires.

Right now it's just the tune under 3k RPM that's a bit sluggish, but I guess it's keeping my rods from snapping. Basically the throttle response is not 1:1 or is limited under 2k or so. The 350Z never had this problem, and it felt great. It might require more skill on the foot, but I rather deal with that than a lazy response.

How many miles do you have now? Have you taken a look at the throttle bodies? That's what I plan to do sometime in August whenever I have time to work on the car.

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scionide

I had a very similar issue, it was in my tune, though I'm not sure what about the tune caused it. It would happen after the car warmed up, I checked to see if it was my brake switch but messing with that did nothing. After getting my car re tuned the issue was gone.

DIGItonium

Mine right now is happening as the car is warming up or starting up after the engine is already warm. It takes about 5-10 minutes for the throttle start opening up. I can see this by monitoring the boost with my foot planted in 2nd or 3rd. At 4k RPM it barely makes 2-4 PSI, and it ramps up slowly. Once it starts opening up, though it easily hits and exceeds 5 PSI at half throttle.

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juld0zer

i have 52000km so about 33k miles. Throttle bodies appear fine but i have never removed them from the manifold collector tk inspect the dirty side. I have bypassed the coolant lines completely so they do feel stone cold after a good run - would that cause an issue? Definitely no subzero temps here though so i doubt ice formation.

i have a Scanguage II in my car so i can watch some parameters live. When i am experiencing the issue, throttle position (TPS) gets pegged at 25 degrees max. Even with my foot to the floor.

What do you guys think about the MAP sensor theory? if the throttle plate opens no more than 25deg under full load then there would be a lot of vacuum right? I'm not sure how vacuum for brake booster is managed on our engine but my guess is that under certain conditions, the throttle flap closes slightly to generate vacuum - thus avoiding the need for a separate vac pump

tjlazer

Sounds like the issues that have been discussed on here for years. The lag off the line when engine temps hit 180+ Mine did it before my UPREV and it's still an issue after, even with Fan Control Mod. I am thinking heatsoak is the issue. It never happens when Engine oil temps are under 180.

I was able to get Intake temp readings with a OBD2 reader and saw Intake temps go from 90 to 180! That's why it bogs off the line sitting at a red light for a few minutes!

aftermarket intake experience

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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

this is definitely not the heat related timing pull lag.

i'll get a video recording next time it happens but if you flick thru my logs posted on the first page of this thread, you'll get all the data and a good baseline to comparw against

scionide

Mine wasn't just a lag either, it felt like I had no power or just wasn't WOT all the way to redline, in any gear. It also took more effort to take off in 1st compared to normal, had to feather the clutch for longer.

Even if my car wasn't hot, as long as it was running for about more than 15 mins and well warmed up, this no power state would happen on my previous ecutek tune. Wish I could tell you exactly what it is but I'm fairly sure it's something in your tune, based off your description.