3 replies to this topic

[NLinPEN]

Hello all, my first post here. I could not find a similar topic in the search so I try a new topic.

 

My car has SPi and automatic gearbox. The issue I'm facing is that when I start the car and then push the brake pedal the engine dies. I have tried a few things but those did not help to solve the issue.

(1) I replaced the four vacuum hoses as a previous owner had installed ordinary rubber hoses (which I didn't like). I discovered that the fuel trap was clogged, so I installed a new one. This did not solve the issue.

(2) The vacuum tube from the manifold to the brake servo looks very old and wasn't flexible at all. I replaced this, plus the inline non-return valve. This did not solve the issue.

Then I ran an experiment to see whether the brake servo is leaking: I disconnected the vacuum hose from the manifold to the brake servo. And temporarily plugged the connector at the manifold to avoid a vacuum leak here. The behavior was unchanged, so my conclusion is that it is not the brake servo that's causing this.

I now don't know what else I should check.

 

This is what I am observing: I start the car with the gearbox in P and the handbrake on, without pushing the brake pedal. The car revs normally (initially approx. 1000 rpm, after a couple of seconds approx. 850). I then push the foot brake and the engine stalls immediately. I tried to give it a bit throttle (e.g. 1,500 ~ 2,000 rpm) and then push the brake: the same happens, the engine stalls. Stalling is not limited to low (idle) rpm only.

I am not sure whether this problem is specific to SPi cars, or that other Mini's have it too. As a starter have I posted it in this SPi forum section.

 

Are there any suggestions out there? What could I investigate to find the cause of this problem?

[weef]

You appear to have covered the brake servo side of things and any related vacuum leaks by plugging and replacing the appropriate pipework.

If you are sure there are no vacuum related faults I can only suggest that there may be some electrical problem.

I would first try starting the car as normal, pressing no pedals, if all is fine stop the engine, press the brake pedal and try to start the engine. Depending on what the result of this test is i.e. if the engine starts or not depends on how you move forward. If it starts I will need to give things more thought. If the engine does not start , take the wire off the brake light switch, start the engine again and press the brake pedal to see if it makes any difference.Try this and see what results, if it makes no difference and the engine still stops I will have to give your problem more thought.

Another thing to check is to make sure there are no wires being trapped under the dash  when the brake pedal is pressed.

[coopertaz]

first thought was also servo diphragm but you seem to have ruled this out above, so check around brake pedal and linkage in engine bay to see if it fouls anything when operated

[NLinPEN]

Thank you both for your replies. Today I continued my search. It is indeed pointing in the direction of an electrical failure. I disconnected both wires from the brake light switch (at the brake pedal). Now I can push the brake pedal and the engine won't stall: it keeps on running without the slightest difference in engine sound or revs. However, if I don't push the brake pedal but connect the two wires from the switch together the engine immediately stalls. This gave me the impression that there might be a heavy load on the battery, or a short circuit. I removed both light bulbs from the rear. Now I can connect both wires and the engine won't stall. The (aftermarket) third brake light is still connected and works during this test. This confirms that there is no short circuit in the wiring in the car. Both light bulbs seem to be fine, nevertheless I exchanged them for some spare GLB380 light bulbs. Even with only one light bulb installed the engine stalls. Then I recalled that I have done a lot of testing over the last couple of weeks, started the car many times over, and might have drained the battery. I have put it on a charger and will check tomorrow whether that made any difference. If so, that would make me wonder whether the ECU measures the battery voltage? Does the ECU switch off in case of a too low battery voltage? This car is relatively new to me, and I don't know exactly how the ECU performs.