1.4 TDCi throttle behaviour
Discussion
Hello,
My wife's car is 2007 mk5 Fiesta 1.4 TDCi, and it exhibits some strange throttle behaviour.
When stationary, the throttle response is quite good, with the engine responding to your foot in a quick and linear fashion. You can blip the throttle quite readily. However, as soon as the car moves the throttle response dies away completely and getting the engine to rev requires a press-and-hold of the throttle.
This behaviour seems to be related to the car moving - as soon as the car is doing 0.5mph the throttle response disappears. It's quite weird. It happens regardless of the car being in gear, clutch up or down. You can be blipping the throttle, let the car start rolling and the throttle response will turn to sludge.
This makes the car rather sluggish and unresponsive to drive (it's very easy to stall pulling out of junctions). The car is clearly capable of much better throttle response, however it seems as though the throttle response has been deliberately reduced, perhaps to make the car easier to drive smoothly for dimwits.
The car would be much nicer and sharper to drive if the throttle response the car has when stationary was available when the car is actually moving! Has anyone any ideas how to make this possible (short of unplugging the wheel speed sensors!)?
Many thanks,
ND
My wife's car is 2007 mk5 Fiesta 1.4 TDCi, and it exhibits some strange throttle behaviour.
When stationary, the throttle response is quite good, with the engine responding to your foot in a quick and linear fashion. You can blip the throttle quite readily. However, as soon as the car moves the throttle response dies away completely and getting the engine to rev requires a press-and-hold of the throttle.
This behaviour seems to be related to the car moving - as soon as the car is doing 0.5mph the throttle response disappears. It's quite weird. It happens regardless of the car being in gear, clutch up or down. You can be blipping the throttle, let the car start rolling and the throttle response will turn to sludge.
This makes the car rather sluggish and unresponsive to drive (it's very easy to stall pulling out of junctions). The car is clearly capable of much better throttle response, however it seems as though the throttle response has been deliberately reduced, perhaps to make the car easier to drive smoothly for dimwits.
The car would be much nicer and sharper to drive if the throttle response the car has when stationary was available when the car is actually moving! Has anyone any ideas how to make this possible (short of unplugging the wheel speed sensors!)?
Many thanks,
ND
No, you misunderstand.
An experiment: gear in neutral, clutch pedal up, left foot on brake on a slight incline. Blip throttle stationary, engine blips happily. Continue blipping as you release brake. As soon as the car starts to roll, (bear in mind, gear, clutch and engine load haven't changed) the throttle response turns to sludge. The car starting to move under its own momentum is the only change.
An experiment: gear in neutral, clutch pedal up, left foot on brake on a slight incline. Blip throttle stationary, engine blips happily. Continue blipping as you release brake. As soon as the car starts to roll, (bear in mind, gear, clutch and engine load haven't changed) the throttle response turns to sludge. The car starting to move under its own momentum is the only change.
I know - it is quite weird. I repeated the experiment time and time again, and each time the car kills the throttle response whenever the car is moving. Very frustrating. I can only think it's done deliberately so that the engine seems responsive when stationary, but has a very soft delivery when moving to make it easier for the lead-footed to drive smoothly.
I imagine this behaviour is hard-wired into the ECU and not easily corrected. Is it even possible to alter the throttle maps via the OBD2, or would the ECU need to be re-mapped?
I've googled this a few times and can't find anyone reporting anything similar, although I'm guessing not many people heel n' toe their TDCi's so probably don't really notice!
This is why I prefer cables. You know where you are with a cable! There's nothing wrong with a DBW system in principle, but it does sadly give manufacturer's an opportunity to muck about with what they should leave alone...
I imagine this behaviour is hard-wired into the ECU and not easily corrected. Is it even possible to alter the throttle maps via the OBD2, or would the ECU need to be re-mapped?
I've googled this a few times and can't find anyone reporting anything similar, although I'm guessing not many people heel n' toe their TDCi's so probably don't really notice!
This is why I prefer cables. You know where you are with a cable! There's nothing wrong with a DBW system in principle, but it does sadly give manufacturer's an opportunity to muck about with what they should leave alone...
Hello Max! I'd half-wondered if you'd turn up on this. As usual, your post is very informative and contains quite a few things I didn't know.
I think you're being a bit harsh on the ol' cable throttle by saying they make cars difficult to drive. I don't have memories of people kangarooing their cars down the road and struggling with stalling back in the 90's when the majority of cars still used mechanical throttles. In fact, this Fiesta is the most stall-able car I've ever driven – you have to learn to press-and-hold-and-wait on the throttle before you can pull out of a junction. Want to get into a gap quickly? Don't bother.
In my personal experience, your point that a mechanical interface results in 'high non-linear torque responses' isn't really relevant – it might be non-linear on a test rig, but in real life it was intuitive and consistent. Again, in my experience I've found mechanical throttle cars easier to drive than DBW cars – mechanical throttle responses were more predictable, and more immediate, whereas DBW cars usually forced me to behave in a certain way and to make allowances, like just giving up on heel n' toeing, or accepting there will be a big pause when I re-apply the throttle mid-corner. As a car guy, I hate this.
On the subject of my wife's car (she bought it before I knew her!) your point about torque slew rates changing in different gears is very interesting, and I think might bear out in driving the car. From first gear, a stamp of the throttle elicits a reluctant and ponderous response, however a similar off/on prod of the throttle in fifth seems to yield a slightly quicker response.
In the case of this car, however, the neutering of the throttle really does seem excessive. As I said, when stationary the engine revs quite reasonably and it doesn't seem to result in any greater vibration or harshness, or at least not more than that horrible little engine usually does. However, someone in Ford Marketing (can I really blame this on Engineers?!) seems to have decided that a throttle response of less than 1 second is clearly unnecessary and the throttle turns incredibly sludgy as soon as you try to move. This does not make the car easier or nicer to drive, regardless of the engineering or marketing logic behind the decision.
As you say, this behaviour is probably hard-wired into the car, and would require substantial work to rectify. My preferred solution is to buy a Toyota Celica instead, but sadly she's not having any of it! At least my three cars have cable throttles – shock horror, one of them even uses carburettors!
Is it really true that you couldn't get a manual throttle car to pass emissions? I could accept that if DBW throttles were mapped to reflect the response of a manual throttle – I can fully believe this is possible – however, maddeningly, car manufacturers seem to think a straightforward, intuitive throttle response isn't something we want, certainly not in mass-market cars. I've said it before: in this brave new world, driving fun seems to be reserved for the privileged - the rest of us just get horsepower when the computer says we're allowed.
Ah well, bring on the google car. I'm going to dig out my dwell meter.
I think you're being a bit harsh on the ol' cable throttle by saying they make cars difficult to drive. I don't have memories of people kangarooing their cars down the road and struggling with stalling back in the 90's when the majority of cars still used mechanical throttles. In fact, this Fiesta is the most stall-able car I've ever driven – you have to learn to press-and-hold-and-wait on the throttle before you can pull out of a junction. Want to get into a gap quickly? Don't bother.
In my personal experience, your point that a mechanical interface results in 'high non-linear torque responses' isn't really relevant – it might be non-linear on a test rig, but in real life it was intuitive and consistent. Again, in my experience I've found mechanical throttle cars easier to drive than DBW cars – mechanical throttle responses were more predictable, and more immediate, whereas DBW cars usually forced me to behave in a certain way and to make allowances, like just giving up on heel n' toeing, or accepting there will be a big pause when I re-apply the throttle mid-corner. As a car guy, I hate this.
On the subject of my wife's car (she bought it before I knew her!) your point about torque slew rates changing in different gears is very interesting, and I think might bear out in driving the car. From first gear, a stamp of the throttle elicits a reluctant and ponderous response, however a similar off/on prod of the throttle in fifth seems to yield a slightly quicker response.
In the case of this car, however, the neutering of the throttle really does seem excessive. As I said, when stationary the engine revs quite reasonably and it doesn't seem to result in any greater vibration or harshness, or at least not more than that horrible little engine usually does. However, someone in Ford Marketing (can I really blame this on Engineers?!) seems to have decided that a throttle response of less than 1 second is clearly unnecessary and the throttle turns incredibly sludgy as soon as you try to move. This does not make the car easier or nicer to drive, regardless of the engineering or marketing logic behind the decision.
As you say, this behaviour is probably hard-wired into the car, and would require substantial work to rectify. My preferred solution is to buy a Toyota Celica instead, but sadly she's not having any of it! At least my three cars have cable throttles – shock horror, one of them even uses carburettors!
Is it really true that you couldn't get a manual throttle car to pass emissions? I could accept that if DBW throttles were mapped to reflect the response of a manual throttle – I can fully believe this is possible – however, maddeningly, car manufacturers seem to think a straightforward, intuitive throttle response isn't something we want, certainly not in mass-market cars. I've said it before: in this brave new world, driving fun seems to be reserved for the privileged - the rest of us just get horsepower when the computer says we're allowed.
Ah well, bring on the google car. I'm going to dig out my dwell meter.
AW111 said:
re Max's post :
I have a 1999 NA engine with factory quad throttle bodies controlled by cable.
While I enjoy its characteristics, you do have to be aware of them, eg
If you floor the throttle at low revs, it bogs down. For best acceleration you need to feed in the throttle to match the revs.
If you jump on and off the throttle rapidly at higher revs, the car will lurch unpleasantly.
Neither attribute bothers me, but a DBW throttle would eliminate them.
See also CV carbs eg SU vs butterflies.
In a way, you're agreeing with me. Although there are engine characteristics of which you have to take account, the response is logical and you're still in control. If you want instant response, you can crack the throttle open for an instant response within the characteristics of the engine; if you want a smooth response, you open the throttle smoothly. With DBW mapped by the manufacturer's, stamping the throttle yields a pause followed by a smooth response, and being smooth with the throttle yields a pause followed by a smooth response. The choice is taken away. I guess the answer to that is the 'sport' button available in newer cars - are any of them linear? Or do they simply allow you to swap between a spongy map and an over-hyped map?I have a 1999 NA engine with factory quad throttle bodies controlled by cable.
While I enjoy its characteristics, you do have to be aware of them, eg
If you floor the throttle at low revs, it bogs down. For best acceleration you need to feed in the throttle to match the revs.
If you jump on and off the throttle rapidly at higher revs, the car will lurch unpleasantly.
Neither attribute bothers me, but a DBW throttle would eliminate them.
See also CV carbs eg SU vs butterflies.
AER said:
You missed the point about power levels having more-or-less doubled and torque even more so. A non-linear system works OK when the maximum result is a limp biscuit. Not so much when you can destroy your shopping trolley tyres in a couple of sittings.
I didn't miss that point. Bear in mind, to quote MT 'It's not a Ferrari'. We're talking about a Fiesta with a raging 67bhp. An incredibly soft fuelling map isn't really needed to stop it tying itself in knots, and yet the manufacturer's have made a rather dull and unresponsive car even duller and more unresponsive. It would almost be better if it didn't have a relatively responsive throttle when stationary. It would at least be consistent.Max_Torque said:
Not to mention back in the day, everything was N/A. so flywheel torque was at any given engine speed, proportional to pedal position. Today, everything is turbo'd, and torque is absolutely NOT proportional to throttle position even at a fixed engine speed.......
That's a very interesting point - particularly when people want Turbos but without the characteristics. Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff