Stalling when applying brakes

[proveitwithdata]

Working on a 2001 sentra 1.8 xe with a stall problem when rapidly depressing the brakes and Im lost.


SIL told me they threw in a new MAF and IAC (oem) and did the pedal dance to reset the idle.

Tested the brake booster and it checked out fine. Fuel trims are -3-3. Checked for any visible or audible vacuum leaks.

Is their something Im missing here in terms of nissan logic?

 

[dumkid]

It's an automatic/cvt?

 

[Warstud]

Vacuum leak comes to mind but I see you checked it .

 

[proveitwithdata]

It's an automatic/cvt?

A/t Jatco 4 speed

 

[dumkid]

Does it stall if you put it in neutral before stopping?

 

[supton]

I wonder if the brake switch is an issue, maybe it isn’t unlocking the torque converter?

 

[proveitwithdata]

Does it stall if you put it in neutral before stopping?

stall scenarios:
Shift into D/R, apply chocks/parking brake
begin rapid brake application, stall

Shift into P, idle at 850 rpm as per nissan fsm
begin rapid brake application, rpm drops a few hundred but doesnt stall

While driving, with the ac on, at stop light.
car will try to stall or stall

 

[proveitwithdata]

I wonder if the brake switch is an issue, maybe it isn’t unlocking the torque converter?

point of note. I asked the SIL, a few years ago brake light switch and cruise bushings were replaced.
in addition the jatco seems to be having issues. Fluid was replaced 50k ago and the fluid is still dark red, but I can feel it shudder on part throttle during 30-40 mph. punch the throttle and its shifts down.

 

[proveitwithdata]

update, i was brainstorming, and decided to see how the vehicle would perform without a maf sensor.

vehicle runs wonky, idles poorly, as expected. However, when i tried pumping the brakes in park, the idle steadily rides up before plateauing at 1.2k.

 

[twX]

Recently, while data logging on my Subaru, I noticed that my MAF reading would drop a bit if I was on the brakes while stopped. So, naturally, I started pumping the brakes like a madman to see what would happen. RPM dropped a lot and engine almost stalled, AFR went very lean then very rich, then everything settled back to normal after releasing the brakes for a couple of seconds.

It seems like it's normal for the brake booster to affect idle vacuum pressure. It could be that your brake system is fine, but your engine is in a poor state of tune that makes it sensitive to disruptions. Low idle rpm, poor spark, lean fuelling at idle from bad O2 sensor, low compression etc.

 

[mk378]

A properly working brake booster dumps a bunch of unmetered air into the intake when the brake pedal is first released from a stop. That doesn't disrupt driving much since the driver usually pushes the gas pedal at that time anyway. By testing the booster I assume you turned the engine off and confirmed that it holds vacuum to boost the pedal for the next 2 or three presses. Then it should get hard to press.

With a detected sensor failure, the PCM goes into a "keep the engine running at all costs" fail-safe mode. So that doesn't prove much about what it is going to do in normal closed-loop.

The brake lights are a significant electrical load and will cause the alternator to demand more hp from the engine.

I'd agree with @twX, it is not running well in the first place.

 

[dubber09]

update, i was brainstorming, and decided to see how the vehicle would perform without a maf sensor.

vehicle runs wonky, idles poorly, as expected. However, when i tried pumping the brakes in park, the idle steadily rides up before plateauing at 1.2k.

In that case, go from exhaust forward toward engine.
Check cat, O2 sensors, what do you see in live data scans? How does that affect fuel mix, lean, reach?

 

[Warstud]

From the info you provided ....... it looks like as you increase the load the car stalls . Possibly a weak Fuel Pump so Check Fuel Pressure .

 

[proveitwithdata]

Update: I was only able to pull some logs pre-MAF replacement, and it seems in gear, STFT is around -3, upon rapid brake application, STFT becomes positive to about +3.