Odd Issue: S-Mode and A/C

DIGItonium

I started noticing my car acting funky today with the A/C running. For a long time I never liked running the A/C since it kills throttle response making it difficult to get smooth shifts. After getting test pipes, the response got better so it wasn't as laggy.

However, today I notice the throttle is acting funky. When I depress the clutch pedal and change gears, the throttle blips and holds for a little bit. I know S-Mode helps with upshifts, but the timing was so odd I had trouble getting smooth shifts. Once I turned off S-Mode, I was able to get smooth upshifts without the weird pre-mature throttle blipping.

Even without the A/C running, I'm starting to notice S-Mode not holding revs properly or at all. In between shifts, the RPM drops way too quickly, which jerks the car. I try to manually hold the revs by keeping my foot lightly on the throttle or rev it higher before switching gears.

All of this started happening the past few days.

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6spd

I noticed that happen in my old Z's last year or so. The RPM's weren't as exact as they had been previously. No idea why, it just happened.

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falconfixer

Digi, it's not throwing any codes or anything? I wonder if a low level fault is in the system that someone with a reader can catch. I know you've been around here for a bit so how's the belt looking? Maybe it's starting to slip with the increased drag from the A/C condenser running? Just throwing random easy ideas out there aside from the usual "disconnect the battery" trick.

DIGItonium

No codes. A/C is running fine. Just some oddities with S-Mode. Clutch depress, change gear, and rev hold kicks in before I even get to lift the pedal. It's just odd and throws off my rhythm. Downshift rev match seems to be working fine, so I've not had any issues with that part.

I wonder if it's the flywheel. Seems like it's making more noise, and it's a single piece from Southbend that ZSpeed sells.

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DIGItonium

Okay, so it's not really the A/C, but really S-Mode.

Half the time I have trouble getting smooth engagements in any gear, and I notice the RPMs drop quick then S-Mode tries to rev match at some awkward moment. I turn it off, and the RPMs drop slower so I'm able to get smooth engagements. Downshifting with S-Mode active doesn't seem to give me any problems.

It's just weird why the RPMs drop so quickly and rev match a bit out of sync. Basically I purposefully depress the clutch pedal, shift into gear, and let the engine rev down. It'll rev down quick, then the throttle blips slightly.

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juld0zer

interesting mate.. i'm snooping around here trying to find a solution to my problem. essentially it's at the point where i think i can rev match better than the car (and i'm terrible at it).

if yours coincides with the aircon on, i'd say the aircon compressor might kick on as u press the clutch pedal in, so the engine RPM drops (which really it shouldnt because the ECU should raise the idle to compensate). so one of the computers (TCM?) is trying to compensate for reduced engine speed to determine how much to blip the throttle?

im having trouble with up and down shifts.

DIGItonium

The throttle is too laggy or the engine isn't as eager to rev, and this makes it difficult to blip the throttle. It was easy with the 350Z. With the 370Z, it's like I have to briefly floor it just to get it to rev a decent amount... overall, too slow.

A couple of things to notice when I had this issue was that the car was slow to up rev when I up shift. Depress the clutch pedal and upshift without releasing it, and you can see the delay before the up rev. The issue I felt was that there were times it was either too late or it didn't up rev at all, which threw me off. Maybe my RPMs were too low, but higher RPMs seem to help a bit.

I just had a new belt put in yesterday, so I've not notice much issues. The last belt started to fray at the threads. So far I haven't noticed it, but I've not tested the A/C either.

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juld0zer

i thought you cured the sluggish response with a new brake pedal switch? or was that something different. from memory you experienced a limp mode-like reaction at the lights.

it's a real shame that it seems Nissans have quite a few common problems yet no real effort seems to have been invested to fix them for good in future models. eg.
- dead throttle response on take off due to defective brake pedal sensor(s)
- clicking noise from axle spline/hub area due to lack of (suitable/adequate) grease applied during factory assembly
- Air mix door motors/doors in the HVAC system failing due to lack of lubrication and/or materials not durable enough. Resulting in self destruction of said door.

Just to confirm, your foot is right to the very end of the clutch pedal travel each time yeah? So far it sounds to me it's the gear lever sensor but try backing out the lower clutch pedal sensor a bit. Backing it out will result in the system blipping a tad earlier. Measure how much of the thread is protruding prior to adjustment so you can revert back if result is no discernible difference.

It's early days for me but i think i fixed mine. My sloppy SRM action (not enough blip resulting in rough unpredictable shifting) was due to fine metal particles stuck to the tip of the input speed sensor. The sensor is on the left side of the gearbox almost perpendicular to the rear cat flange. I found no visible damage to the loom due to heat or physical damage.
Think of the crap that gets stuck to a magetic engine oil sump plug. That's the amount and fine-ness of this silvery coloured substance i found on the tip.
From my experience with these type of sensors, any metal on the tip can interfere with signal production.
The same type of sensor is responsible for sloppy shifts in automatic transmissions of orher cars.
There seriously wasnt much of this material on the sensor but cleaning it was enough to restore smooth up and down shifting at various rpm. No more holding breath as i re engage clutch!
I will report back in 1000km to see if it holds up. but i will look into fitting a magnetic gearbox drain plug to keep those metal particles at bay.