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

Guys, I don't want to bother and bore you. For me personally it is also an interesting topic to learn something. My good friend Mike from Chicago would approach the topic the other way round as I did. His opinion is valuable to me because he develops software and hardware for a known company.

Getting confirmation on the intentional type of switch is important for debugging.....So when not pressing the brake pedal, your throttle BPS switch should register a connection. It's quite possible in my mind that your NO switch is damaged or misaligned?

The engineer in me would hook up some test leads and monitor the voltage at the ECU. If there was ever an intermittent disconnection along the entire path of the wires, then the ECU would register a brake pedal press and cut fuel. It could also be as simple as the brake pedal being calibrated too sensitive and the bouncing from its own momentum causes the switch to disconnect briefly, etc....

I think for a more reliable behavior, I would probably short the two wires together? Just to make sure the fuel map is running in the normal mode? Or does it actually flip back to normal after extended disconnection is detected? I'm wondering how it responds to temperature differences, etc...

But I guess that's a lot of work when you're happy with the changes you've experienced? Like I said, it's that engineer desire to fully understand the entire system, haha.

Me again:
i have a feeling you got it right. it's a good idea to just bridge the switch to try if it also works fine this way. Well, the opposite of what I did. You're right, this way it would remain exactly at the intended setting of all parameters. Maybe the ECU is ok but the switch wiggles uncontrolled between open and closed.
These switches are known for inferior quality anyway.

This has been a fascinating post and something to look forward to hearing more about each day. I do hope that Heinz and Stuart will keep us updated as time progresses so we can see the final solution confirmed.
Brilliant stuff. Thanks guys.

Interesting stuff Heinz,

I like your friends thinking on pedal bounce and the possible affect of temperature, Though I suspect you may not have sent him the pics of the switch set-up showing them located on the floor and subject to picking up crud and perhaps even a degree of water ingress, as he might have mentioned that too..? Intermittent faults can be a real pain to identify and never more so when connected to an ECU/PLC as an input..

George, you are right, such a search can become a nightmare. I sent him the pics of the switches mounted respectively the link to this thread. I will give his suggestion a go to make both wire ends with direct contact. Of course in the whole path a bug in the wiring can be hidden but that would be a point of start. He is right that only this way I can be sure that the parameters for normal driving are keeping correctly, at least as long as someone in the know could tell that the parameters will be the same each way.

He commented the picture of the brake pedal with this words:

My guess from looking at the mechanical design of your brake pedal configuration that it's an issue of "underdesigned overtravel". Overtravel is the spec for how far the switch plunger can travel after the actuation point. The switch will get damaged if it's ever allowed to overtravel. It only takes one time of overtravel to permanently deform the parts inside the switch.

Heinz, thanks for the update, guess we can just the general switch spec and pedal interface design to the list of Morgan ..err.. foibles…(-:

As opposed to just introducing a shorting wire, I might be inclined to temporarily wire in a flick switch which can be operated while you are driving...That way you might advance your thinking on the way the programming works under different situations...

That is a valid point as well Luddite to use for a while such a switch! Even if the car drives subjectively well with the circuit always open it could be the case that the parameter are not as intended for normal drive. E.g. the engine brake force keeps stronger. Just to mention one point I can directly notice. So I will see what happens if I can switch to a permanently closed circuit before I order a new BPS switch.

BTW regarding the switches my friend writes:

I'm also thinking the actuation point for a NO and NC switch in the same switch body is often different. Like you have two switches with the same outside mechanics, but different function inside. The actuation, pre travel and overtravel specs are going to be different. If you are setting the position using the brake light, then it's possible the fuel switch is just sightly not fully engaged and becomes intermittent enough for the ECU to think you're often but not always on the brake?

So many theories that can get ruled out with an oscilloscope 🙂 I'm so blind without that lens....

No problem on the quoting, haha.

On this point I see more the danger of overtravel because both switches are almost fully pressed down due to the brake pedal.

Heinz, modifying Morgans to improve on the specification of standard equipment has been normal practice for many years, perhaps this is something to add to the list...?

As your friend suggests if incorrectly adjusted and there was a possibility of the switches acting as an involuntary stop for the pedal`s spring return(?) then perhaps the switch could be damaged internally..

Update.
It is impossible to overlook in my last posts how euphoric I was after we took out the switch. The main reason was that for the first time the stuttering of the accelerator was gone. But unfortunately the performance got worse and worse after another 100 kilometers. In the beginning the car really drove very well. But the program for the brake action (open circuit) had changed the CPU more and more. The sound of the engine became more and more dull, the exhaust was coal-black and at high revs the performance became more and more asthmatic and the fuel consumption increased. For this reason there is no need for a comparative trip with a manual switch.

So I connected the switch again today. Immediately the jerking was permanent again. I have now the impression that the defective switch had a negative influence on the ECU even at higher speeds and full throttle, even if in this driving condition the jerking was masked.

Now I have implemented the idea of Mike to bypass the switch. So to realize the closed circuit for the driving program without switch.
I must confess that I am very relieved now. Hard to believe, but the jerking is completely gone and the engine sounds very healthy and it yaws for speed. In other words, it runs as it should, as programmed by Ford.

I am also very happy for another reason. I don't have to keep looking for an error any further. Because if this switch bypass hadn't changed anything, I would have had to look further in the wiring harness or in the ECU, which I personally cannot do.

Again for Stuart, I'm sorry if I was so euphoric, but don't drive with an open circuit. If you want to find the fault in the switch, then drive with a closed circuit, as shown in the photo below. Of course, after the picture was taken, we isolated the blank areas with tape.

I am very, very happy now...after a new accelerator pedal, a new MAF sensor, a new coilpack, another throttle body and a lot of stupid trying around.

I owe it to the forum that I became aware of this switch in the first place. And I owe it to the switch that it was so consistently bad in the end. Because nothing is worse than finding a mistake that only occurs twice a week.
Unbelievable how badly such a cheap switch can cause damage by permanent loose contact. So, for me the search has come to an end, thank heaven. If I order another switch I will see... And sorry about the crumbs in the footwell.

Absolutely agree, which is why I used the term "expected logic". I think you mis-understood my explanation on Roadster operation though. The brake lights operate conventionally with no electronics intervention. The powertrain module is just wired in to be aware of brake pedal action as well for whatever reason.

Note also my comment earlier that the switch trigger logic can be reversed by mechanical location and actuation. Something to be aware of when considering the switch function logic.

Hello Hienz, I admit I’m still a bit confused by the explanation of what to do next , so
1. You disconnected the switch - no stuttering but gradually worsening performance
2. Reconnect switch- stuttering still there- switch is faulty?
3. Bypass the switch - stuttering is gone, car is healthy?

So you are driving with the circuit constantly connected (as if never using the brakes) and the car is working perfectly ( over how many kilometres?)
Surely this means that you are gradually confusing the ecu again?
It seems that you have a faulty switch (and so do I!). I tested mine and it seemed to be working, but the fault was intermittent. Did you test yours?

I am going to order a new switch from Melvyn. I will try the car before and after I fit it, and compare.

The saga continues!!!!