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

juld0zer

i got my car back from the dealer.
i had a list lf warranty issues to fix:
- boot doesnt release on first press (new hatch springs fitted)
- boot struts provide little assistance at upper half of travel (new struts fitted)
- ac/volume controls are jittery (control panel backordered from japan)
- clutch fluid disappearing (slave cyl replaced)
- severe lag when at operating temp...

i took the tech for a test drive when i picked up the car. they blamed my stillen intakes but i argued. they said the cam and crank sensors are fine even though i pointed them to the exact page in the service manual.

the fault did occur during the test drive. tech tried to mask it by demonstrating that it 'is normal' by driving aggressively (launching at 2500-3000+ rpm and keeping revs above mid range). i pointed this out that the car shouldnt have to be driven like that all the time. he took the car into the workshop and brought it back out for me to drive home and monitor its progress.

i have to say, whatever happened in the workshop prior to me taking the car home seems to have cured it. i cant seem to make it happen. i've crawled home thru traffic a few times, driven it hard and gently. so far so good. rpm still sags to 500rpm at idle sometimes.

as for the slave cyl, my clutch feels better than the day i picked up the car 2nd hand with 15000km on the clock! pedal is heavier but has more feel. gearshifts are really smooth. 1st to 2nd no longer clunks. rev match is pretty much flawless.

let's see how she goes

P's_Z

Good for you juld0zer! I should be taking mine in sometime the following week, things at work have been hectic but hopefully i can get Monday off.

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Zeta

juld0zer

looks like my joy was short lived. it was inevitable that the issue would eventually resurface but now it is more difficult to reproduce and it will occur in unpredictable circumstances. before i took it in, it would happen pretty much within 25mins of casual driving from the first start of the day.

so far i've had it happen mainly after driving for about 35mins or more, or whenever the coolant temp stays above 90*c for a while. but there was one time during a 1.5 non stop drive including heavy traffic crawling where the lag did not occur at all!! so that occurrence certainly makes my temperature related theory a bit muddy.

i was due for an oil change today. changed the oil to Valvoline 5w30 MST with the same model mobil 1 filter (108). Prior, i was running Nulon 5w40. viscosity is important for the VVT solenoid function so if Nissan designed the engine for 5w30 worldwide, i will run 5w30 until the issue is sorted (got lots of 0w40 and 5w40 at home)

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