Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Aero 8 S4 Fly-by-wire throttle

I notice when accelerating in my S4 (manual) that the first c.1 inch of throttle pedal travel delivers no engine response. Thereafter it performs perfectly. It's rather like having some cable slack in a cable connected throttle. It's a little frustrating when braking and wanting to "blip" the engine revs between gear changes.

Can anyone tell me if it is possible to adjust this "slack" out.

David

Sounds like throttle position raw min and max and actual have not been set right. I think you should get the ecu readings for the throttle position sensor checked.

I don't know about Aero -specific FBW throttles, but you will probably find that the pedal site is measured by ascertaining the difference between two potentiometers, one running 0 to 5V and one 5V to 0. The ECU will map these voltages to specific pedal sites. It is probably set to ignore small variations or differences in voltages. Beware that if you get someone to remap these, you may well end up with a very sensitive throttle.

It is a standard feature of most FBW throttle systems these days that they don't permit fast throttle blipping. it's bad for emissions and not necessary for smooth changes. Unfortunateley it does have some significant side effects liek slow throttle response.

But I find the compensations more than enough. I get over 200bhp/tonne out of my 4/4 and 38mpg, so I'm happy to give up a bit of throttle blipping!

To be honest I don't spend a lot time blipping the engine revs between gear changes. It was just an easy way of describing the effect. I've always liked the accelerator on my cars to respond straight away rather than there being any slack: no particular reason, just preference. So in the past, particularly with my previous Morgans, I've always removed any slack. But it was a bit easier with throttle cables! I shall investigate a bit more but if there's no easy fix I'm sure I shall get used to it.

Thanks for the technical detail - it's always interesting to find out how things work.

David

I suspect that a great deal will ultimately depend on how much the BMW engineers have done to the map to suit the physical installation in the Aero.

It's possible that they haven't changed the sensitivity map for the pedal position sensor from the standard BMW installation - which means that if the Aero installation has a different pedal arrangement with a different range of movement, then the 'dead zone' could be caused not by the map, but by the revised pedal layout: a different arc of movement would generate a different rate of movement in the pedal position sensors.

If you have a look at the hinge end of your throttle pedal, there will be some kind of linkage to convert the essentially linear movement of the pedal to the actuation required by the pedal position sensors - which are almost certainly going to be simple potentiometers, and thus probably with a rotary motion. If there is some kind of adjuster here, there may be a mechanical fix to the 'dead' zone at the start of the pedal travel - it may be as simple as adjusting a pedal stop screw. But as I said, I haven't had a close look at the exact way this is done in the Aero, so I may be blowing smoke here - I'm just extrapolating from my general knowledge of how FBW throttles work, and how it has been implemented in my car.

The danger here of course is that you adjust the pedal stop position to give a nice pickup, and then you find the pedal pad itself is now in an awkward or uncomfortable position for your foot.

With my 4/4 VVTi conversion, I found I had to bend the arm about quite a bit to give me the positioning I wanted - fortunately easy because the shaft itself is mild steel. But what's fine to do with an out-of-warranty car with a completely non-standard engine conversion may not be wise to attempt with a rather more valuable Aero, still under warranty :-)

Thanks for this - I'll have a look this week-end.