Tachometer RPM Needle Bounce

[Superteeth]

Hello everyone. I noticed something odd today in my car. When I accelerate lightly (shifting at about 2250 RPM, usually from 4th to 5th and 5th to 6th), the RPM needle bounces a bit (about 100 RPM, down and then up and down to the correct RPM) right after the shift. I do not hear a corresponding change in the engine speed, but that may be because the change in engine speed is not enough to hear a difference. This does not happen when I accelerate hard. What could be wrong?

[EZcheese15]

Hello everyone. I noticed something odd today in my car. When I accelerate lightly (shifting at about 2250 RPM, usually from 4th to 5th and 5th to 6th), the RPM needle bounces a bit (about 100 RPM, down and then up and down to the correct RPM) right after the shift. I do not hear a corresponding change in the engine speed, but that may be because the change in engine speed is not enough to hear a difference. This does not happen when I accelerate hard. What could be wrong?

It sounds like you might just be lugging the engine. Shifting at only 2250 RPMS is pretty early. Try shifting at a higher RPM. Also, 100 RPMs is barely noticeably on the gauge anyway, are you sure that's all it is? It doesn't sound like it's much to worry about.

On another note, your profile says 2012 G37, is it not under warranty? And I'm assuming you have a manual transmission since you said you are shifting, or do you have an automatic that you are shifting yourself (via paddle shifters)?

[Superteeth]

I guess I was a bit unclear when I said that I "shifted" at 2250 RPM. Since I have a 7AT, what I meant was that I give enough gas to cause the computer to shift at about 2250 RPM. But this also happens when I use the paddle shifters to shift at about the same engine speed. I would guess that I was not lugging the engine when using the paddle shifters to shift at this speed since the computer does so all the time (and even shifts at as low as 1500 RPM).

Also, a correction: This occurs only on the 3-4 upshift, and 4-5 upshift, and only when I give enough gas to shift at somewhere between 2000-3000 RPM (it does not occur when I accelerate harder, or lightly enough to shift below 2000 RPM).

Is it even possible to lug an automatic? Presumably the computer would have the transmission downshift if you attempted to accelerate in too low of a gear. I also know that if you attempt to shift too early using the paddle shifters, a beeping noise is heard and the upshift is not allowed to occur.

[EZcheese15]

No, I was assuming you had a manual since you said you shifted it.

If you have an automatic, the computer is controlling everything. If you aren't feeling anything, and only seeing the needle move, I would ignore it. Because the throttle is also controlled by the ECU, I'm guessing it is quickly adjusting the intake valves to match the throttle to correspond to the drop in RPMs after the gear change. The slight fluctuation in the needle is probably just picking up the quick engine adjustment after compensating for the gear change.

[Superteeth]

Why does it only happen on certain gear changes, and why did it never happen before? Also, is it possible that the small change in engine speed is simply imperceptible to me?

I really seem to be prone to worrying, especially since the car was so expensive. But I do not want to go to the dealership because they may make things worse, and the needle fluctuation is not causing any issues in the car that I can tell.

So to clarify, it should be impossible to lag an automatic transmission car, right? Thanks for helping out.

[EZcheese15]

Why does it only happen on certain gear changes, and why did it never happen before? Also, is it possible that the small change in engine speed is simply imperceptible to me?

I really seem to be prone to worrying, especially since the car was so expensive. But I do not want to go to the dealership because they may make things worse, and the needle fluctuation is not causing any issues in the car that I can tell.

So to clarify, it should be impossible to lag an automatic transmission car, right? Thanks for helping out.

It makes sense that it only happens in higher gears because you have less torque in the higher gears, causing it to be less stable when shifting. I'm guessing you just didn't notice it before.

And no, you can't really lug an automatic because the computer is controlling the shift points, so the only lugging it will do is taken into account by design.

[Superteeth]

Alright, thank you. One last question, if you do not mind answering. Why does this not happen on the 5-6 and 6-7 gear shifts, if it is due to low torque in higher gears? Thanks again.

[audtatious]

Try resetting the ECU. I don't have a 7sp A/T and neither of my G's with the 5sp A/T do this.

Anyone else with a 7sp notice this?

[Superteeth]

Re-setting the ECU by disconnecting the battery for some time and re-connecting it? Or do I need to go to the dealership to get the ECU flashed?

While searching online for what my problem could be, I noticed that a lot of 350Z owners seemed to have the problem that I have. The problems may be related.

[audtatious]

Battery drain does not fully reset the ECU. Check this thread for some additional procedures to try:

post6422673.html

[Superteeth]

So this should work if it is a problem with the ECU, even if there is no check engine light? I guess I will try it out.

[audtatious]

You may have codes even if there is no check engine light as well.

If this does not solve anything then drop it off at the dealership and tell them to fix it. If they say it's normal then go for a test drive in a loaner 2012 to see if it happens. If it does not happen then the dealership will have to do further research into the issue.

[Superteeth]

Well, I did want to avoid the dealership if possible, but I guess that if this does not fix it I will have to go. Thanks for the help.