Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Diagnosis please?

Sorry if I said it wrong, Stuart, my BPS switch is absolutely top notch. I had to interrupt its current flow to get the car running again without that awful jerkiness. And with your car, it could be the same reason.

Uther has confirmed what I suspected that there are intentionally different switches.
Richard (+8Rich) said in this thread that his 2009 4/4 also had two switches. That one was still Euro4. Of course it might depend on the different programming of the software. The diagram above only shows that this switch can be used to influence the accelerator pedal value. And exactly this I notice very painfully as long as the circuit was closed. So again my question...why is it a NO version of the switch? To me it would make sense only the other way around and using a NC switch. Then, the brake would influence the accelerator pedal when needed during braking and not when driving.
Luddite, I am very sure that the brake lights do not go through the ECU but only through the fuses.

Many thanks for conformation that the brake lights are not wired through the ECU Heinz, It is good to know that some of my logic might still be applicable on occasion, though with aircraft falling out of the sky because a whole team of " expert" programmers and others "never thought of that" entirely flawed sequence of operation.....!!!

Except on the 3.7 Roadster which has only one brake switch to operate lights and provide a trigger to PCM.

Regarding the type of switch that Heinz was considering, if used solely to provide an ECU trigger, it could be either NC or NO depending on the expected logic.

Bingo! Correct wire colours too. Thank you Jon

BY shows again on the right of the diagram you sent. Is this an Earth?[/quote]

Yes is given ref Chassis Earth on layout

This is the 'body harness' bit showing the other switch

Richard thanks for the heads-up on the 3.7 Roadster`s ECU dependant brake light operation... No real surprises there then..Call it evolution Shrug..!

Logically, as an input device a designer can select either NO or NC, though replacement of any such switch in a system the choice must be on a like for like basis.

I also called my Morgan garage now. They're always very experienced and helpful, as in this case. They confirm that the BPS sensor is a NO switch...so if the brake pedal is not depressed the circuit is closed.
According to the expert, the main purpose of this switch is that you cannot press the brake pedal and the accelerator pedal at the same time wanting to drive further. However, the expert has said that if both pedals are used repeatedly, the effect of stopping will remain off.
The reason is that if both pedals are pressed repeatedly, the driver's intention becomes apparent to the ECU and it will give way. The classic case is drying the brake after washing, where the expert says that he has to press both pedals (or just the BP, I forgot) twice and then the car will drive on with the brake and gas pedal pressed at the same time (of course gently).

If everything is in order and functional, then the ECU should ensure that driving is possible without disturbance even if the BPS circuit is closed. Because, as I understood it, the "decision-making authority" lies with the ECU. And it cannot intervene in this case if the BPS switch is removed. (Richard Wood says that triggers are possible in both directions, changing to open or to close, depending on the circuit, here it is the case obviously that it triggers when changing to open - activating by pressing the brake pedal down - when I am right).

But if, as in my case, the throttle closes unintentionally sporadically while driving, then I should leave the cable disconnected from the BPS switch, said the expert of my garage as well. Because it can be that the ECU itself does not "cleanly" keep it permanently "digitally open" when normal driving...or maybe the ECU needs an update. Because, with an update such irregularities are mostly repaired, so the experience of the expert.

At the end he said (very rightly) that I should continue to observe whether the error has really disappeared forever. The side-effect and great benefit is that the car drives better than ever before when she drove with the "digital" open BPS circuit.

So, all in all I am happy now and I will see if the failure keeps away, what I think it will. And others with the same issue can have an easy try, be it the repair of the interruption or addressing the overall throttle pedal quality.

Sorry Heinz our posts crossed.
So the switch passes current when the brakes are not in use.
One side of the switch feeds from the throttle pedal, the other is to Earth.
If the switch fails,
A) it either interrupts the feed from the throttle, creating the same effect as using the brake pedal, or,
B) It doesn’t interrupt the circuit when you do press on the brake.

In my case, more throttle overcomes the problem.
In Heinz’s case, leaving a wire off the switch creates case A), so his car should not maintain power - but as reported, he’s got a power boost!

I now understand that your advice was that the ecu has learnt to interpret the BPS wrongly and so over-rides it most of the time. We should then disconnect the switch for a time, and the ecu will re-learn normal driving, rather than react wrongly to the BPS.
I take it that the wire can be restored eventually.

Hope I’ve got that right. I’ll drive with the wire off the BPS for a while. I think I’ll also try to find that Earth and clean it

Stuart, when you can drive again, just try it, I am very familiar with this „more throttle“ makeshift solution.

I owe you a beer if it will not work.

Stuart, I've only just now seen your post. I'm not sure how the wires of the BPS run exactly. But in any case, the control unit plays a role. What it does exactly when it's working wrong or right, I don't know. I also do not know how many other variables, e.g. other sensors, also play a role. I only understood that for driving there should be no unintentional wrong intervention of the ECU. To avoid this I have prevented the ECU from working on this special job (among many others which the ECU has to manage further on) by keeping the BPS out of the way, so the circuit is always open.

Ok happy to claim that!