Hey I've had my SSM Sport Manual for about a month now. I've only read in a few places about the tendency for the engine to keep reving after you lift off the throttle during moderate to heavy acceleration. Is there a way around this, besides not accelerating as hard? Someone also said that it shifts smoother if the engine does that. I'm still a novice at stick, so can someone explain why rev hang would make the shifts smoother? From the passenger's point of view it just sounds like the driver doesn't know how to use stick.

 

It's not so much that it keeps revving higher, but that it maintains the revs for a split second after you get off the gas in a shift. It's done for emissions sake, and there's nothing you can do about it to make it go away. Realistically, it's no big deal -- it just makes the car feel like it has a heavy flywheel somewhat. You just have to get used to the timing when you shift and after a while you'll never even pay attention to it.

 

How does it help emissions? Does it not use any gas as it maintains the revs?

 

What I've read is that when the throttle closes suddenly the lack of air leads to unburned fuel dumped in the exhaust, which will damage the catalytic converter.

I don't really follow that explanation, though. Doesn't the ECU control each injector pulse directly? It should be able to cut the fuel in sync with the closing throttle.

 

It's not that it can't do it, it's programmed not to; i.e. -- the ECU is programmed to hold the revs. The Fit has an electronic throttle which is controlled by the ECU, so you have no direct connection to the throttle body. You let off the throttle, and the ECU keeps it open just a split second longer, long enough to burn off the unburned fuel, etc.

 

Is there any other car that does this?

 

I believe the new SI's do, I know they have an electronic throttle and do recall hearing the revs hang somewhat as well. The 2nd gen S2000 also has drive-by-wire, though whether it hangs the revs or not I have no idea. Merely having an electronic throttle doesn't mean a car will hang revs, though, it's still a function of the ECU programming.

 

Yes, the ECU controls the throttle and the injectors. So where is this unburned fuel coming from? That's what I don't understand.

 

I notice this delay in the throttle response when you lift as well.

When I was researching the Fit and its competitors, I read that the Versa also has this issue with hanging revs. But they apparently had a ECU program update for it. The only thing we can hope for is that enough Fit owners bring this to Honda's attention and they will issue a reprogram as well. Otherwise, we're stuck with it since it's drive-by-wire.

 

Most cars with an electronic throttle are programmed to hang. Everyone that I've heard of, anyway. The Si's rev hang was somewhat disturbing at first and it's something you either get used to or you don't. I recall GTIs and 350Zs, as well as numerous others having the same issue, although it's a lot less noticeable in factory turbo vehicles since they generally have some kind of lag anyway.

The TSX also uses an electronic throttle (or DBW) but it's still physically connected by a mechanical cable.

 

I don't think it's a good thing honestly. This was a recall to FIX on the new 06 Civic Si's. After seeing before and after videos of the reflash, the no rev hang seems much better, more like the older non DBW cars. I think this is just a DBW issue that needs to get fixed. I'm hoping if all Fits have this rev hang, then a reflash is in order. Honda did so for the SI and it helped tremendously, hoping the same for the Fit.

Youtube rev hang civic si, you'll see the issue before and after reflash, it shouldn't be there, manual transmissions should drop instantly after letting in clutch...

 

Is this the reason why shifting is so jerky, or is it just me?

 

If, for whatever reason, it's programmed to hang for a noticable fraction of second, it should hang at exactly the rpm required for the next gear. That would make for extremely smooth shifting.

(Excuse me, I need to go phone the patent office....)

 

haha that'd take some great programming but it would be awesome.

 

It's practical, I think. The ECU can tell the load is gone from the manifold pressure (on future cars, switches to tell it that you've actually pressed the clutch or shifted into neutral would help). It can tell what gear you're currently in from your speed and RPM. It can tell whether you're shifting up or down by whether you're decreasing or increasing accelerator pressure. And it can calculate exactly the RPM required in the next gear at the current speed. So for the next second, it can adjust the throttle and injectors to hit and hold that RPM. Perfect shifts every time, and the clutch and synchros last forever. Somebody needs to do it.

 

I'm a mechanical engineer. I'll do it. Unfortunately only Chrysler is hiring me at the moment.