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Non Linear Throttle Response.


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#1 termin8r

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Posted 19 December 2012 - 05:24 PM

Hello everyone. I'm new to ford ownership. Bought a pre-reg with 0 miles smax in October. It is 2.0 TDCI zetec. Already had the window motors replaced on the front. Bad start..

Next issue seems to be the non-linear reponse from the accelerator which causes difficulty in taking off from stopped. If i press the accelerator slowly whilst in neutral , there is no reponse from the engine. At a certain point it then jumps straight to around 2000rpm or higher. Why is this? My friend you co-incidently bought the same car seems to have the same problem although i have not tested their car.

ECU anomaly?
It certainly makes the car hard to drive without either conking out or revving it excessively,

Any ideas?

Sam.

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#2 FOCA

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Posted 19 December 2012 - 05:59 PM

There may be a number of reasons for this -

1 - The throttle is a potentiometer (variable resistor) it sends an analog signal to the ECU - (like a mouse on a computer) it is not connected directly to a carb or thottle bodies like in the "old days" it is far more complicated than that - the symptoms you are experiencing may have nothing to do with the throttle itself (as you have suggested)

2 turbo lag, these engines can suffer from turbo lag, where the turbo takes time to boost up, it can be worst off the line/ in the lower gears

3 power band - the engine may have a "power band" where the power & torque is in a relatively narrow band - for example the engine may be "gutless" below 2k, then there is a sudden rush of power, then the power drops off above 3.5k - some engines are like this - the mondeo TDDI was like that, and the PSA Mondeo 162 is like that -

a remap, bluefin or tuning box can help this

4 - there is a microswitch on the clutch pedal - this sends a signal to the ECU to "!Removed!"/ restrict the engine, this stops you from revving the engine when the clutch pedal is down, "slipping" the clutch "racer" style, by reducing the power/ torque during a change (all this protects the DMF/ clutch and is supposed to smooth out the gear change ) - i have disconnected this switch on my car and it makes a big difference, gearchanges are sharper, engine picks up better etc (i return it back to normal for snow etc)

5 the Maps/ setup of the engine may be biased towards emmisions/ economy throttle response/ drivability may be a low priority in the way the car is set up - again, a remap/ tuning box would help here, or perhaps an update on the manufacturers map

6 - all this stuff may be (is) interconnected, it could also be connected to the EGR and DPF

7 - anti stall - ECU is boosting the revs to prevent stalling? and otherwise reducing revs for better emmisions/ economy

you probably have the PSA engine, a joint venture including Peugeot amd Citroen

#3 termin8r

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Posted 19 December 2012 - 06:46 PM

Thanks for your response. I also have another car which is petrol and "fly by wire" accelerator also. It idles around 7-800rpm. When i (in neutral) press the accelerator extremely gently the revs rise slowly as expected and it is a very linear and smooth response.
In the SMAX it idles around the same but pressing the accelerator in the same manner results in no increase in engine revs until a certain point where it just snaps to 2000rpm or above.
This symptom would indicate point 1 or 5 above. It is not turbo lag or clutch related as I am in neutral and the car is not moving.
I ran the ford garage and they told me to ring the technical number. But at £1 per minute, why should i have to do that on a new car??

Just wondering if anyone else has an 2012 smax and whether it does the same thing.


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