147 TS throttle behaviour?

[bazzbazz]

I would simply put it in 3rd or 4th gear, floor it till it started to run out of steam then slowly reduce throttle to see if there was a corresponding reduction in engi e speed/power.
Or is that over simplifying things?

[johnl]

Baz,
I've played this way already, though in 2nd and 3rd gears. Flooring it in 4th until it "runs out of steam" gets a bit faster than is wise on the public thoroughfare...

What I have found is; with my car (pre pedal mod), with the pedal flat to the floor and rpm climbing into the higher reaches (but not nearing redline), that the pedal can then be lifted about an inch or so before there starts being any obvious reduction in acceleration, then deceleration.

This moment is accompanied by a subjective sensation of the car very briefly accelerating even more than with the pedal fully on the floor, from the instant the pedal starts being lifted to the instant the deceleration starts being obvious. This is obviously not a real thing, the car is not actually accelerating harder for this brief moment, it is a false perception related to the conscious and subconscious expectation that the car should begin to decelerate at the very moment the pedal is lifted, but it doesn't. It's like when you brake on a very slippery surface and the brakes lock up, the car feels as if it acelerates, even though this is an impossibility (physics don't you know...).

Keep in mind the subjective nature of this 'test', and that attention is split between 'observing the test' and not crashing the car.

Regards,
John.

[johnl]

For anyone intrigued enough by my experience with this, it would be very easy to repeat the experiment. All you'd need is a small block of wood and some duct tape.

I'd be interested if anyone had a seemingly similar result, or if I'm just going a bit gaga in my old age...

Regards,
John.

[bazzbazz]

All you'd need is a small block of wood and some duct tape.

Images from Indiana Jones & the Temple of Doom come flooding back with Short Round driving like a maniac through Shanghai.      

[johnl]

I've been wondering whether this phenomena (seemingly more power at partial pedal throttle than pedal WOT) might be less to do with absolute butterfly opening, and more to do with the ECU defaulting to a very rich AFR in WOT open loop mode (as it is my understanding is a common practice, because the rich AFR is very 'safe'), and the rich mix resulting in some power loss.

So, I went looking on the web and found nothing definitive to support the idea, but a few things suggesting it might not be a crazy notion.

I've stolen the following explanation from some Mazda enthusiasts forum. I'm not saying this is unarguably a correct diagnosis of the issue, but it does pretty much mirror what I have been suspecting. It is a succint explanation, so rather than rewriting it I'm just cutting and pasting, with attributuion to 'Josh'. 

"The reason there is more power at partial throttle than full throttle is because of the ECU's fuel delivery system. At WOT, the ECU basically dumps the maximum amount of fuel it can for that particular engine speed. This is called "open loop" operation because it ignores feedback from the O2 sensor. At partial throttle, the ECU is still operating in "closed loop" mode, where it injects the appropriate amount of fuel based on engine speed and O2 sensor readings. So at partial throttle, there is a more stoichiometric mix in the combustion chamber, providing a quicker, more complete burn, which ultimately results in more power.

This practice is the same for just about every car I've heard of, turbo or not. The intention is to avoid detonation at WOT by making the fuel mixture as rich as possible. This is not a problem or anything the dealer can address. It is a common design for fuel injection. It merely requires a little more attention to detail when learning how to drive your car fast.
-Josh"

I somewhat disagree with some of the last paragraph, I think it is a problem. Still happy with my lump of wood...

Regards,
John.

[johnl]

It seems nobody is attempting to replicate my experience with this...

With more familiarity all I can say is that my engine is now much more 'fun', feels significantly more 'lively' than before, and even the gear shifts feel better (maybe rpm drop starts to occur slightly more quickly in response to pedal lift, because the pedal doesn't have to come back / up through that part of the pedal travel that increases power above what WOT seems to produce?).

My speculation is that maybe the TB is at least a bit bigger than it really should be, or, that WOT causes the ECU to default to a 'safe' open loop map wherein the AFR is so rich that it is affecting power, or, that with WOT something (i.e. detonation, mapping?) is causing the ignition timing to become somewhat retarded, or some combination of the above.

If the TB butterfly is not reaching fully open (with reduced pedal travel), and it isn't too big, then this might suggest that more improvement could potentially be possible (if full pedal travel were reinstated) if the ECU could be 'persuaded' to remain in closed loop when the butterfly approaches / reaches fully open...

It's all a bit weird, but I'm pretty sure I'm not imagining this.

Regards,
John.

[Citroënbender]

I've been reading with some interest, you really need a second car of identical spec (without modifications) to validate the postulations though. 

[johnl]

CB,
Of course you are completely correct to imply that what I am describing is an utterly subjective experience. This is a data free zone so far, and the engineers' credo should be kept in mind; "in God we trust, all others must provide data". For my own purposes with this I am happy to accept the feedback from my arseometer...

However I don't think that a second car is needed to validate / quantify this. One car and a rolling road would do it.

For experimental purposes the mod itself is dead easy, a block of wood and some tape to hold it in place. So it costs almost nothing to try it (unless you just have to have data, and so were to be paying for dyno time). But before that, I'd try the 'hold it flat to the floor and then back off a bit' experiment first.

If the car seems to accelerate a tad harder at some degree of partial throttle than it does actually at full throttle, or ever seems to not start slowing as soon as the pedal is backed off from the floor, then I think there is an issue worth exploring...

Regards,
John.

[Citroënbender]

I'm just trying to convince you to acquire a second 147. Purely for experimental purposes, of course. 

Have pondered the behaviour you describe on and off.  A question came to mind; the interplay of intake tract and variator solenoids against the ECU map.

The other more general comment is, driving a car in the city you want pretty instantaneous acceleration from a dead or near stop, but not to insane speeds. Possibly the car is programmed with this in mind?

[bazzbazz]

Don't forget kids, the Variator cuts in at 3000 rpm.

[Citroënbender]

Irrespective of load and throttle position? I'd have credited it with more sophistimacation.

[johnl]

I'm just trying to convince you to acquire a second 147. Purely for experimental purposes, of course. 

Last thing I want / need / have time / funds for is another car...

Have pondered the behaviour you describe on and off.  A question came to mind; the interplay of intake tract and variator solenoids against the ECU map.

It is a question, and I have no idea how to investigate or answer it. However I have no reason to think the variable intake tract and / or valve 'variator' are not working as they are supposed to, and don't suspect these things to be a problem or player here with this issue, but I can't say either one couldn't be...

The other more general comment is, driving a car in the city you want pretty instantaneous acceleration from a dead or near stop, but not to insane speeds. Possibly the car is programmed with this in mind?

I suspect this to be a potential motivation for why a manufacturer might fit a slightly oversized TB (or at least to err on the oversized side), i.e. for a given engine size and all else being equal it would tend to create a 'zippy' feeling when accelerating from rest to moderate speeds, or from low to moderate speeds, i.e. typical urban operation. Of course if the TB were excessively oversized then the car might become somewhat more difficult to drive, with too much response for a small throttle opening.

And another of course, a similar 'zippy' characteristic could be achieved electronically (I presume), i.e. just how the TB butterfly responds to pedal input, one not necessarily equalling the other. It could likely be done either way, i.e. mechanically or electronically, or maybe both ways at once...

With my car, limiting the throttle pedal travel has not resulted in a discernible reduction in higher speed acceleration. If anything it is better the higher the speed. It is also much better for pedal modulation when backing off / on /  off etc. at higher speeds / rpms / larger throttle openings. Now, a small lift has a significant affect, rather than a large lift being needed for a significant reduction / increase in power.

Previously, once past X pedal position, the response to the pedal became 'doughy', whether hammering down or lifting off. Lifting off was weird, because lifting the pedal from the floor would initially cause no reduction in power, or even a slight increase (at least it sometimes felt like a slight increase). This meant that (from pedal on floor) quite a big lift was needed to make a modest reduction in power.

I will say that I rarely rev this engine over 5,500rpm. There is just no point as there is little power increase above this, and the gear ratios are close enough that shifting at 5,000 to 5,500rpm doesn't drop the engine out of the power band (i.e. below 3,500rpm or so). This is the same now as it was prior to limiting the pedal travel.

Regards,
John.

[johnl]

Don't forget kids, the Variator cuts in at 3000 rpm.

CB responded: "Irrespective of load and throttle position? I'd have credited it with more sophistimacation."

"sophistimacation"...?

I thought it was 3,500 rpm, but I really don't know. Would it not be possible to rig up a dash light that illuminated whenever the variator was activated? This would give some idea of just how strictly the variator was locked to rpm, or how much the point at which it activates 'floats' depending on other inputs...

Regards,
John.

[Citroënbender]

From memory you can see its status on the ECU parameters listing with MultiECUscan. It's a two person job, though - one to drive and the other to observe.

[baldrick]

Ok, I'll bite.... what's a variator?