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

I’ve just returned from the supermarket run in my 4/4...... I held the throttle still at a constant 50mph in 4th gear whilst braking slightly with my left foot. The car just slowed down because of the braking and thats all, the engine did not show any signs of cutting out.

I’m sorry I can’t answer your question, I’m not familiar with the Sigma. But re the sensors, looking at the picture I think you will have an Accelerator Pedal Position Sensor and a Throttle Motor Position Sensor (B138 & B169).

Fortunately for me the +4 Duratec ECU was discontinued by Ford in 2006 so does not have some of this ‘clever’ stuff.

If as you can see in the Ford Focus schematic the second switch on the brake must be interrupted when you don't brake then I have the wrong switch. Thanks to this thread I am only aware of this switch (brake pedal sensor). My son and I have tested it thoroughly. It conducts electricity when you don't touch the brake.
The background is that the 4/4 has again this interruption since I changed the airfilter recently.

While other measures to repair the stuttering gas were always of limited duration, today we disconnected the switch. The car drives very constantly without the slightest interruption of the gas pedal. I will repeat both constellations over the next few days. Then I will have experiences which are no longer determined by coincidence and which lead to the assumption that the reason for the error has been found and that the error can be caused intentionally.

And there is something else as well. The car drives much better, as if it had always had to fight against the intervention of the current-conducting brake pedal switch since I had it. It sounds fuller, it accelerates more vehemently and the gas pedal is more sensitive. This means that everyone who has a 4/4 that doesn't stutter but has (perhaps also) the wrong switch will benefit.

In North Rhine-Westphalia we are allowed to drive a car without giving reasons. I don't have to overdo it but for testing purposes in not nice weather and in boring surrounding I use it.

I will report whether this measure is permanent. I have a very good feeling. Without wanting to say anything negative, it is possible that a whole series of 4/4 got the wrong switches, if we assume that the Ford focus schematic is correct. Intuitively I would say that the schematic is correct because you would have an open circuit under normal driving and you would send an impulse for what purpose ever (stopping fuel, deactivating a speed control etc.). If the good results are confirmed I will buy a switch that works the other way round. It is also obvious that an unattractive interruption is exactly what the switch is supposed to do...if it does it at the right moment for the right purpose and not at the wrong moment.

A note of caution, please ever disconnect any wiring which leads to the ECU before making a measurement of this switch.Not only to get the right impedance values but in first line not to damage the ECU because any impedance meter is using active current.

For those who are curious if the car drives better when the switch is out of function (or to see if it is the right or as in my case the wrong one), you must not demount anything because on the left side the cable can be pulled off easily with your fingers.If your switch is correct nothing will change, if not you may have a more pleasant drive experience. Please insulate the end of the teared off cable plug.

Heinz

From my understanding of what you say, both the brake light switch and brake pedal sensor should only have a current flowing when the brake pedal is pressed down/depressed.

If your brake pedal sensor has current flowing/ ie a circuit when the brake pedal is NOT pressed down/ NOT depressed then it sounds like your brake pedal sensor has an internal fault.

Replacing the brake pedal sensor switch should confirm this shouldn't it?

Rob, your conclusion when and when not the current should flow is absolutely correct.
I didn't examine the brake light switch yesterday but I assume that the current only flows there when you step on the pedal. In other words only when the push button of the switch comes out. Such a switch resp. BPS would be needed as well.

I have disconnected and insulated the wires of the BPS which is technically the same as an open circuit when not touching the brake pedal. And now the cars runs very good without a fault. Of course I will monitor it in the long run and report.

The switch is really not damaged at all. It is ok working. It reads 0,001 Ohms in closed position and infinity when open. It is controlled and stable working. But it works the wrong way around, it is a wrong item. So after 5 years of driving this beloved car it was the first time yesterday that the throttle pedal and the reaction of the engine feels „right“.

My intention and concern is that it could be possible that I am not the only one who has a 4/4 with such a wrong way working (not damaged) BPS beside that I think I have found the reason for the interruptions.
The subtle thing is that the car can drive without jerking, with a closed circuit...or even with jerking, or just sometimes with jerking. But if the BPS works the wrong way round then drivers who have installed such a BPS never have experienced their engine running when the circuit is open.

Well done Heinz, I know you were very sceptical about the functioning of the 2nd brake pedal switch when I first mentioned it in the thread and as I no longer own a 4/4 Sport couldn't prove it to you one way or another which was a little frustrating in my attempt to help the OP

Heinz, in the UK an on off type of switch, may be identified by the operation of it`s internal contacts.

Normally Closed (NC) or Normally Open (NO) when the switch is not being operated.

Thus in the case of a spring loaded push button switch it will be selected and identified as either NC or NO dependant on it`s desired function.

Both an NC or NO switch can look identical physically though their internal switching function is entirely opposite from each other..

Hope I have not added confusion.

Hi Heinz

I expect Melvyn Rutter will know if both the brake sensor and brake switches are the same part and they aren't expensive at £6.30. Hopefully you have found the intermittent fault with your car and probably Stuarts is a similar fault too.

So fingers crossed for a solution to both your and Stuarts problems!

ADDENDUM... Should perhaps have added that if the switch has four terminals, then two of them can be NC and the other two NO when the switch is not being operated..

OR if the switch has three terminals each of them may an identification NO, NC, and COM com equating to being common connection to both NO and NC dependant on the position of the switch, thus either NO or NC will be chosen relative to the desired action required..

Many thanks, Richard, George and Rob. Yes I was sceptical re the BPS and in another sense I am still so.
George that is a very helpful information. So „normally closed“ when not operated is the right switch for both, Brake Light and BPS because it is all the time operated by the brake pedal (pushed in) to stay open when not braking.
I will check which item Melvyn Rutter has on offer to replace the BPS because I need the NC version anyway.