Drive by wire.

[Dave Plowman (News)]

My old Rover SD1 has just about the earliest EFI on a UK car. Basically Bosch, but the ECU made by Lucas, who also did the mapping. The TPS on that is a vast carbon pot which does wear out - at about 100,000 miles. Luckily, Vishay make a conductive plastic generic type which can be persuaded to fit, and being just an electronic product, under half the price.

There are no diagnostics on early Lucas injection, so it requires some skill to fault find. But electronics fault finding is usually well above the pay grade of the average garage fitter.

Lucas produced a number of test sets to make it easy for them - basically good or bad LEDs in a box. At vast cost. Which tell you nothing a DVM can't.

[Dave Plowman (News)]

Could be. The fact that it happens just above idle - where a pot would get the most wear - made me wonder if it was.

I've looked up spares on Ebay. Of course it doesn't say how it works. But does appear to have more than the three wires you'd expect with a simple pot. And looks nothing like one - more like an electric motor.

[Dave Plowman (News)]

The fault I have is nothing to do with idle control. Although I suppose the same servo that opens the throttle could be used for that too. Mechanical throttle systems usually had a separate idle valve.

[Dave Plowman (News)]

With some of the super long warranties now available, the days of cost cutting to that extent may be gone.

But I don't know what a Gray encoder is either. ;-)

[Capitol]

Thel last one I had trouble with used a stepper motor at the engine end. The problem showed up as an idle error, but was actually a faulty oxygen sensor which via the on board computer was causing the wrong setting of the stepper motor, but only when hot. It came and went which was very frustrating, the diagnostics did not show the faulty sensor, it was only by replacing all the bits one by one, that I cleared the fault.

[Dave Plowman (News)]

Just to try and clarify what it is to those who still don't understand.

It merely in essence replaces the throttle cable. Could be used on a carburettor car if you wanted to. Doesn't need to interface with the ECU of an injection system - although may well in practice.

[David]

I had an intermittent drive by wire fault on the Fiat Ducato camper (2001 engine/chassis).

This was also intermittent and more likely to happen when warm.

The effect was that it wouldn't accept anything less than half throttle, which made for interesting driving.

The engine warning light did come on during the fault condition, though.

After the main dealer finally getting the diagnostic kit to work it turned out to be intermittent throttle sensor (or near offer). They then checked through all the wiring for the throttle and found a couple of poor connections. Once these were cleaned up then it all worked fine.

Cheers

Dave R

[Dave Plowman (News)]

I'd certainly considered a poor connection, as the car is low miles and I'd expect such a device to last for at least 100,000 miles.

Just hoping the dealer finds the fault. There was no warning light. I'd expect anything which stored a code to give a warning something is amiss? Of course this sensor doesn't *have* to be connected to the ECU.

[Andrew]

£400 is the part price. You also need to fit it and use a diagnostic kit to tell the ECU about it.

Post number 10.

[Andrew]

Break open a stepper motor and you should find one. Instead of a variable resistance that gives an analogue output (which can vary with wear) a grey encoder is a series in interlaced fingers with a slider that passes across them and the output is normally a series of pulses that the ECU can count. Presumably avoids the need for an analogue to digital encoder and analogue calibration. A grey encoder only needs a method to tell the ECU when it is at a zero position.

[Dave Plowman (News)]

So there is still a sliding contact of sorts? Bit like an old stud fader?

I'd have thought contactless Hall effect etc would be the way to go these days.

I've bought a pirate copy of the Porsche factory manual off Ebay for 10 quid. Everything in PDF format. Shows the pedal value sensor (Porsche speak) as being a twin pot device.