Acceleration Cutting Out.

[andrewwynn]

Originally Posted by Peezen

I’ll try your test on a little hill shortly and report back. Is it just a light tap as opposed to a full brake press? Or would both things cause it?

Just enough brake for the light to come on.

I noticed this happen when I tried to "brake stand" and turn my tires like I used to with my Z28. The engine got to about 3000 RPM before it coughed and sputtered.

[andrewwynn]

Originally Posted by nick325xit 5spd

The brake override that BMW has requires fairly high brake pressure AND high throttle as I understand it.

I did have the brake on fairly firm so it may in fact need pressure but wouldn't fit the symptoms here so I think just brake on at all will after time kill engine power.

My e53 is "down for the count" at the moment due to a deer committing suicide by BMW so I can't test it. I just recall instantly thinking I broke my engine trying to turn my tires while not moving.

[Peezen]

Ok so I ran the test and two things happened. First I used the Creader to monitor brake light switch function as live data, then I drive to the bottom of the hill.

When I started up the hill and pressed the brakes a bit the live data changed to ‘operated’ and did not change back to ‘not operated’ once I took my foot off the gas.

It didn’t cut throttle this time, though I was going pretty slow and didn’t drive long. When I got back into the driveway I pumped the brakes a bit and once again the brake light switch live data switched back and forth from ‘operated’ to ‘not operated’. I tried it in drive as well just to make sure that it does indeed change while driving.

Is there a brake override live data option I wonder? I’ll have to have a look.

[Peezen]

This sounds exactly like what my X is doing given that the brake light switch is staying in ‘operated’ position after taking my foot off the gas.

https://auto.howstuffworks.com/car-d...de-systems.htm

[nick325xit 5spd]

Originally Posted by Peezen

This sounds exactly like what my X is doing given that the brake light switch is staying in ‘operated’ position after taking my foot off the gas.

https://auto.howstuffworks.com/car-d...de-systems.htm

I can tell you that all of my BMWs will let me drag the brakes on throttle well past the point where the brake booster runs out of booster. Even the E90.

[Peezen]

Well, I took the panels off to access the brake switch to swap it out and low and behold the switch was all the pushed in, as in it was not even in contact at all with the pedal. I pushed the brake pedal in, extended the arm and the slowly released the pedal and let it adjust the arm.

I took it for a spin with the reader plugged in, active testing the brake switch and there was not even any lag, let alone staying in the ‘operating’ position. I did not have the engine yet and slow me down at all, nice spirited driving action. I’ll obviously keep tabs on the issue and see if it comes back, but man oh man, what a soul crushing behaviour from the X for such a simple and free fix (potentially)!

Thanks for everything peeps, that was really helpful, and hopefully this will help other folks who run into this problem.

[Peezen]

Originally Posted by nick325xit 5spd

I can tell you that all of my BMWs will let me drag the brakes on throttle well past the point where the brake booster runs out of booster. Even the E90.

Yeah but that would be a lot different than you riding on the brakes and gas for minutes at a time, endlessly really.

It doesn’t seem to activate immediately, but when it notices both sensors are activated at the same time for an extended period of time, it tries to slow the vehicle down just in case. Makes sense.

Remember, my code was saying that the brake switch sensor was on permanently.

Thanks for your help!

[nick325xit 5spd]

Originally Posted by Peezen

Yeah but that would be a lot different than you riding on the brakes and gas for minutes at a time, endlessly really.

It doesn’t seem to activate immediately, but when it notices both sensors are activated at the same time for an extended period of time, it tries to slow the vehicle down just in case. Makes sense.

Remember, my code was saying that the brake switch sensor was on permanently.

Thanks for your help!

That is a fair point. Glad you're sorted.

[jdstrickland]

Originally Posted by Peezen

Hi all, happy holidays



Am I looking at an issue with the accelerator pedal? Or the throttle body? To be able to trust my new friend in the winter here I really have to get this issue sorted out, but without any codes to start with I’m wondering if anyone in here has any experience with this?

I would think NOT the pedal or the throttle body, if the pedal was moving but the throttle was not, this should give a code for the failure to see the pedal, or for the throttle body's fail to move as commanded.

The throttle body is a stepper motor, and the pedal is a pulse generator. The pedal moves 15 pulses (whatever) and this tells the computer to command the throttle body to move 15 pulses. Because this is an essential system, I should not be possible that the pedal or the throttle body to fail without the ECU reporting the trouble.

[Peezen]

At this point It looks like it was BMW’s brake override system kicking in because the brake light sensor was stuck indicating ‘operated’ which the computer looks at as abnormal behaviour (pushing the gas while holding down the brake for an extended period of time.

According to the link above the X then goes into a mode where it works to slow the vehicle down to a crawl just in case you’re having an issue.

I readjusted the brake light sensor and it seems to drive fine now.