Tach hang and inconsistent RPM drops

[DeHackEd]

I think the subject says it all, but even the tach hang is inconsistent.

Some days when I'm shifting, the RPMs start to drop quickly and do so at a good rate. Other days when I clutch in the RPMs hang or the engine even revs a bit when the weight of the car is removed from it and then the RPMs casually come down. And yes, I'm careful to come off the gas first, though I still do it as quickly as I reasonably can. The effect can also be witnessed in the form of a delay between coming off the gas and engine braking kicking in. I think the ECU is possessed.

Some days a 1->2 shift is painfully slow unless I want to wear on the clutch more than I really should. Other days it's more what I would call reasonable. I don't know why.

If it matters, my vehicle is as indicated below.

[AHTOXA]

Cue in Mr. Bovine and his love affair with rev hang.

[jomotopia]

if you've got drive-by-wire, that's probably your answer. everyone seems to have these issues with DBW except me.

Some days a 1->2 shift is painfully slow unless I want to wear on the clutch more than I really should.

really, dragging the rpms down with the clutch for the 1-2 shift is not going to wear the clutch that much. it's already slowing down, and that is the clutch's job, to synch the engine and transmission. i think doing this several times is still going to be far less clutch wear than a single normal launch.

[theholycow]

Cue in Mr. Bovine and his love affair with rev hang.

What, me show up in a thread about rev hang? Naw, that could NEVER happen! Really, google only shows 68 results for me posting about rev hang on this site...
http://www.google.com/search?q=site:sta ... ev+hang%22

DeHackEd, rev hang sucks. I hate it. When I take my foot off the gas, I want it to quit making power and begin slowing at whatever rate the flywheel allows. I don't mind if RPM falls slowly, even very slowly, but I want it to begin falling immediately. I don't think it's too much to ask. I don't think it should be a "feature" limited to sports cars; in fact, IMO, rev hang should be the feature limited to sports cars, while grocery getters should not hold the RPM at all.

It's not related to the flywheel. A heavy flywheel makes RPM drop slowly, but it doesn't make RPM hang steady before dropping. It's not related to some stupid safety feature that prevents excessive engine braking on slippery roads. I guess it exists for people who want to take 5-6 seconds to execute a shift.

I usually complain about drive-by-wire throttle, but really, rev hang doesn't require DBW. Newer cable throttle vehicles have throttle actuators, and older ones might be able to use the IACV for rev hang (though it would be less awful rev hang).

really, dragging the rpms down with the clutch for the 1-2 shift is not going to wear the clutch that much. it's already slowing down, and that is the clutch's job

jomo, it's NOT already slowing down. That's the problem with rev hang. It's holding steady. If rev hang happens at 3021 RPM, it will stay at 3021 RPM until the engine can't make enough power to hold 3021 RPM...and if it can make enough power then the car's going to shoot off like you're racing, once you engage the clutch.

I address the problem, as well as improving my fuel economy and reducing engine noise, by shifting as low as possible. When I enter my next gear it's usually near idle and I have just enough power to accelerate reasonably. YMMV.

[jomotopia]

jomo, it's NOT already slowing down. That's the problem with rev hang. It's holding steady. If rev hang happens at 3021 RPM, it will stay at 3021 RPM until the engine can't make enough power to hold 3021 RPM...and if it can make enough power then the car's going to shoot off like you're racing, once you engage the clutch.

i had assumed it would hang for a second and then the revs would begin to fall. surely it won't just stay at 3k indefinitely with you off the throttle? if so that sounds like a more serious problem that wouldn't be considered normal behavior even for a pain-in-the-ass DBW setup. but then i don't have any problems with my DBW so i haven't experienced these things. i still think it's not going to wear the clutch too much to pull the rpms down with it on the 1-2 shift.

[theholycow]

If it only happened for a second it might go unnoticed, since even a quick shift probably takes about a whole second before you engage the clutch. In my car the usual length of rev hang is 3 seconds.

[DeHackEd]

Yeah, it bites.

What really sucks is that it's inconsistent. Sure a 3 second (minimizing clutch wear) sucks, but when it suddenly becomes 1.5 seconds when you hop in the next time - that's what annoys me. The learning curve is jagged.

[gear323]

Guys,

For anyone that has a Volkswagen car, there is a petition online that you can sign if you have the 2.0T engine and have the rev hang issue.

You can read about and sign the petition here: http://www.ipetitions.com/petition/peti ... -rpm-hang/

[theholycow]

gear323, you don't have to exhume every dead thread about this stuff, we get the idea and the people in these ancient buried threads who don't come around probably aren't subscribed for email notifications of their old threads getting bumped.

[Squint]

Guys,

For anyone that has a Volkswagen car, there is a petition online that you can sign if you have the 2.0T engine and have the rev hang issue.

You can read about and sign the petition here: http://www.ipetitions.com/petition/peti ... -rpm-hang/

Don't know if you looked at the date, gear323... but this is a slight necro-thread

[tankinbeans]

Necrothreadia. o_0

[Shadow]

if you've got drive-by-wire, that's probably your answer. everyone seems to have these issues with DBW except me.

It seems that rev hang is pretty common on new DBW cars, but the fact of the matter is that not all DBW cars have rev hang. My car has none at all. And I mean absolutely none. If I didn't know any better, I'd think the car has a cable between the accelerator pedal and the throttle plate.

Another thing to consider is that there are lots of cars that can be tuned to eliminate (or at least greatly reduce) rev hang.

[AHTOXA]

In my personal experience, VW has been the worst for rev hang. I've owned, what, 3-4 vehicles with DBW since then and never had an issue with it as much as I did in the VW. In fact, I don't feel or see it on my current car at all - none.