RPM Hold on Up Shift

[Boogeyman]

So I picked up my car yesterday and while driving around today I noticed that if you slowly upshift the car holds the rpms at the level they should be when moving to the next higher gear. I found this odd but kind of cool. So the manuals don't quite have rev matching but it does look like Ford has been working on it. Anyone else notice this?

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[SVTFreak]

So I picked up my car yesterday and while driving around today I noticed that if you slowly upshift the car holds the rpms at the level they should be when moving to the next higher gear. I found this odd but kind of cool. So the manuals don't quite have rev matching but it does look like Ford has been working on it. Anyone else notice this?

Manufacturers have been doing this awhile. My 91 has he same functions that's tuneable in it. It's gotten better over the years. Some people like it. Some don't.

 

[Norm Peterson]

It's an emissions tweak - suddenly closing the throttle results in emissions spikes (not sure which ones). Momentarily holding the throttle open reduces or eliminates that, and emissions requirements are so tight now that it matters.

In normal, part-throttle driving there really isn't any need to be hurrying the upshifts, and if you do take a little more time this rpm hold will be far less objectionable. Maybe even unnoticeable (I don't notice it in any of my cars unless I'm specifically intending to pay attention to it, which is almost never).


Norm

 

[aeropaul]

It's an emissions tweak - suddenly closing the throttle results in emissions spikes (not sure which ones).

When the throttle is open to hold 3k rpm, the injectors are spitting enough fuel to match the air flow calculated by the MAF to keep a 14:1 Air/Fuel ratio. When the throttle butterfly is closed off suddenly, and before the injectors have enough time to respond properly, this causes the air content of the charge to go down without changing the fuel content. The AF ratio drops causing a rich spike, generating a lot of unburnt hydrocarbons. This is what spikes during sudden throttle close-off.

 

[Boogeyman]

I understand the A/F ratio reasons for not just cutting the throttle completely but that is not what I was talking about really. I am saying the car rev matches on up shifts. It holds the revs at whatever they should be in the next highest gear at the speed you are going when the clutch is depressed.

 

[Horse]

When the throttle is open to hold 3k rpm, the injectors are spitting enough fuel to match the air flow calculated by the MAF to keep a 14:1 Air/Fuel ratio. When the throttle butterfly is closed off suddenly, and before the injectors have enough time to respond properly, this causes the air content of the charge to go down without changing the fuel content. The AF ratio drops causing a rich spike, generating a lot of unburnt hydrocarbons. This is what spikes during sudden throttle close-off.

I am no engineer; but I would rather believe/prefer the following is the case: When gas pedal is lifted suddenly, and before the injectors have enough time to respond properly, the ECU keep letting sufficient air though the throttle. This should make sure that no unburnt fuel will get released to the atmosphere.

 

[Horse]

I understand the A/F ratio reasons for not just cutting the throttle completely but that is not what I was talking about really. I am saying the car rev matches on up shifts. It holds the revs at whatever they should be in the next highest gear at the speed you are going when the clutch is depressed.

Are you saying that the 15 Mustangs (manual) will rev match for you when up shifting?

How about shifting up VERY slowly (say taking 3 seconds)? I doubt the ECU will hold up at the correct RPM for your next gear.

Again, I am talking about stick shift 15 Stangs. The auto should rev match automatically for you (be it up shift or downshift).

 

[aeropaul]

I am no engineer; but I would rather believe/prefer the following is the case: When gas pedal is lifted suddenly, and before the injectors have enough time to respond properly, the ECU keep letting sufficient air though the throttle. This should make sure that no unburnt fuel will get released to the atmosphere.

What you just said is the logical cure for the rich spike condition. Modern EFI systems are designed to enable that type of compensation. Whether it's through delaying/damping of the throttle plate closing action in a throttle-by-wire car, or with an idle-air control valve on engines with a cable-actuated throttle. Air cutoff is metered to reduce rich-spikes and thus unnecessary tailpipe emissions.

Trust me, I am engineer....[ame] really...

And to boogeyman, I was more trying to explain what emissions are increased during uncompensated throttle cutoff, and why.

 

[Boogeyman]

Are you saying that the 15 Mustangs (manual) will rev match for you when up shifting?

How about shifting up VERY slowly (say taking 3 seconds)? I doubt the ECU will hold up at the correct RPM for your next gear.

Again, I am talking about stick shift 15 Stangs. The auto should rev match automatically for you (be it up shift or downshift).

Yes I have a manual 2015 GT w/ PP andit holds the rpms for several seconds. It doesnt rev match on downshifts, which we all knew, but this feature surprised me when I picked it up.

 

[Horse]

What you just said is the logical cure for the rich spike condition. Modern EFI systems are designed to enable that type of compensation. Whether it's through delaying/damping of the throttle plate closing action in a throttle-by-wire car, or with an idle-air control valve on engines with a cable-actuated throttle. Air cutoff is metered to reduce rich-spikes and thus unnecessary tailpipe emissions.

Trust me, I am engineer.... really...

And to boogeyman, I was more trying to explain what emissions are increased during uncompensated throttle cutoff, and why.

Gocha

 

[Horse]

Yes I have a manual 2015 GT w/ PP andit holds the rpms for several seconds. It doesnt rev match on downshifts, which we all knew, but this feature surprised me when I picked it up.

Interesting.

Maybe Ford did write something there on the ECU that holds the rev for you, as you suspected...

 

[KP6Five]

Yeah I just noticed the other day... pretty cool. I also noticed if don't give it any gas in first and slowly let out on the clutch the RPM's will jump up to about 1200. I think this is why I have had some issues being smooth shifting on this car. So the other day I decided I was getting into the gas to early while I was letting the clutch out causing it to not be smooth at all. Also contributing is the late clutch engagement. You have to let out quite a bit on this car. So anyway... I also noticed the RPM maintaining on shifts and didn't touch the gas on the shifts. Then eased into the gas late and it was so much better I can't even explain. I have drove a standard all of my life and can drive anything but this car had me puzzled until this discovery. So I was over compensating for something the car is helping me do. Crazy...

 

[Ruby305GT]

Can a tune take this RPM hold out? I noticed it while changing gears, the RPMs wouldn't drop and it'll just hover over a bit like if I was still accelerating when I was just pressing the clutch. It really throws me off, but I figured I would get "used" to it.


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[TurboAg]

Does the rpm hold stop if you go into neutral and release the clutch?

 

[Ruby305GT]

Not for me when I test drove, more of a feels like you still accelerating right when you shift. I drive a buddies S2000 recently and it did the same thing, must be lack of practice.


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