[wanderhermit]

Originally Posted by bobbyblr

Does Jimny has any sensor to measure the Vacuum generated from the engine that is supplied to the Brake booster? If yes, then should this sensor give the ECU the error message and the dashboard brake light should get ON or something ?

Or may be one should add an external Vacuum Gauge like below on the dashboard:
https://www.amazon.in/ESUPPORT-Turbo...00SMDR3Z2?th=1

This I feel is the best solution to find the problem. Anybody tried this?
Also, anybody tried switching off Micro-hybrd system?

[TheCamShaft]

This is one of an interesting topic to follow that goes across air pressure related behaviours, and tons of learnings . Given initially it was mentioned that at 2k rpm the braking got back to it senses suggests there is not enough vacuum created otherwise unless it was forced enough. It might be an interesting study for MSIL as to if there is a fundamental shift on RPMs side (near idle rpms) at high altitudes with Jimny than what it is at plains, which might also impact the operation of the vacuum pump, and thus vacuum creation capacity. Total respect for everything that is being discussed on this thread. It's been enlightening.

[dsr001]

Any difference in the high altitude brake behaviour with AC on/off ?

[purohitanuj]

Originally Posted by dsr001

Any difference in the high altitude brake behaviour with AC on/off ?

Generally it does. For most petrol cars, if you keep the brake pedal pressed and it the same time of the AC compressor goes off, you will feel the pedal move slightly downward. I have experienced this is numerous cars in Jams ( I mostly drive AT now which means I get to keep the pedal pressed ). One can test this by switch AirCon off with brake pedal pressed. I guess that happens due to sudden spike in RPM when engine is unloaded of the excess load.
In my case, AirCon was on 90% of time.

[SnakemanJohny]

Originally Posted by amalji

Are you sure? I think EGR is present in all modern petrol and diesel vehicles.

I think you are right. EGR is present in MPFI Gypsy, and must be there in Jimny too.

But how is that related to the issue of poor braking at high alt ?

[purohitanuj]

Update [ 08 October 2023 ]

As per my scheduled visit, I reached the service center where I was informed that few engineers from Maruti Suzuki were waiting.
They connected a VCI OBD and started to capture all parameters as a log file while they drove my Jimny and tested the brakes at different RPMs. I too then drove. Nothing out of ordinary was observed.

Note that the VCI does capture the vacuum brake boost pressure in kPA.


I suppose they will correlate this data from another Jimny tested similarly in higher altitude.


The brake fluid filter had this gunk like substance.


Brakes were cleaned. When I asked them to bleed them once, the service engineer told me that they were specifically asked to "not" touch much on the brakes as they didn't wanted to disturb the brake setup too much for future analysis.



However, post the brake cleaning process, the pedal became spongy and I had lost the brakes all together. Hence they had to do the bleed process which resulted into this oil coming out which was filled in by a brand new bottle of DOT3 brake oil.



During the brake shoe removal, a pin ( which is used to hold the brake shoe) broke which might have resulted in the spongy brake pedal.

The pin is marked as part number 6 in red.

As for the update further, I have asked to wait for few days / 1 week.

[sammysossa]

Originally Posted by purohitanuj

As for the update further, I have asked to wait for few days / 1 week.

Great. This is quite heartening to see. Thank you Anuj.

[bobbyblr]

Originally Posted by purohitanuj

Note that the VCI does capture the vacuum brake boost pressure in kPA.
Attachment 2515055

First of all good to get the readings from the Brake Booster Pressure sensor.
I converted the kpa to in.hg and got 20.79 in.hg of pressure for 70.4 kPA.

I suspect that at the high altitude the outside atmospheric pressure is less than at the ground level. So there could be very less pressure difference between the outside & inside the brake booster as per the below graph (Source: Wikipedia). Hence the vehicle needs to check the outside air pressure also.
For example for Leh at an altitude of 3,524 m, the pressure will be around 70kPa or less.

[purohitanuj]

Originally Posted by bobbyblr

First of all good to get the readings from the Brake Booster Pressure sensor.
I converted the kpa to in.hg and got 20.79 in.hg of pressure for 70.4 kPA.

I suspect that at the high altitude the outside atmospheric pressure is less than at the ground level. So there could be very less pressure difference between the outside & inside the brake booster as per the below graph (Source: Wikipedia). Hence the vehicle needs to check the outside air pressure also.
For example for Leh at an altitude of 3,524 m, the pressure will be around 70kPa or less.


Attachment 2515307

I guess they use a 2port differential sensor which has one end exposed to atmospheric pressure to get a relative delta between the two. If it had been an absolute reading, then what you say would be true. Only Maruti would know the implementation.
Then engine uses a vacuum pump to generate this delta pressure. Else how would it know when to cut and start?

[Kosfactor]

Originally Posted by purohitanuj

I guess they use a 2port differential sensor which has one end exposed to atmospheric pressure to get a relative delta between the two. If it had been an absolute reading, then what you say would be true. Only Maruti would know the implementation.
Then engine uses a vacuum pump to generate this delta pressure. Else how would it know when to cut and start?

Does this vehicle have a vacuum pump?

[purohitanuj]

Originally Posted by Kosfactor

Does this vehicle have a vacuum pump?

The engine creates vacuum which is also used for the air locking hubs for the front axles. The manual also state this. Snippet is shown below.

[Kosfactor]

Originally Posted by purohitanuj

The engine creates vacuum which is also used for the air locking hubs for the front axles. The manual also state this. Snippet is shown below.

Yes I read that but wanted to confirm with you since you have been to the workshop, so I guess it uses the manifold vacuum rather than a vacuum pump. Since this vehicle also has VVT, drive by wire throttle and possibly EGR too, my guess (based on why many cars now need a vacuum pump) is that this vehicle applies 'choke' through VVT rather than throttle itself during cold start, so less manifold vacuum available.

Why is it not a problem else where other than high altitude?

I think BHPian bobbyblr`s post about vacuum Hg calculation to Kpa would mean the brake pedal will be a lot harder , probably as good as no booster at all during this cold start condition at high altitude.

[TheCamShaft]

Originally Posted by purohitanuj

Attachment 2515545

Its interesting to see the owners manual also captures the Harder brake pedal condition with right attribution to the low vaccum. So far, this condition- the low vacuum generated by the pump emerges out as the top root cause. The next question would be what is MSIL going to do to resolve this condition as literally this is risking lives at high altitude if vacuum pump's capability isn't good enough to tackle low air pressure conditions at high altitudes. Any ECU updates to manage the other factors such as higher engine RPMs to compensate for that? (assuming this is a camshaft operated vacuum pump, which would theoretically mean vaccum capacity generated is a function of engine rpms)

[purohitanuj]

Originally Posted by TheCamShaft

Its interesting to see the owners manual also captures the Harder brake pedal condition with right attribution to the low vaccum. So far, this condition- the low vacuum generated by the pump emerges out as the top root cause. The next question would be what is MSIL going to do to resolve this condition as literally this is risking lives at high altitude if vacuum pump's capability isn't good enough to tackle low air pressure conditions at high altitudes. Any ECU updates to manage the other factors such as higher engine RPMs to compensate for that? (assuming this is a camshaft operated vacuum pump, which would theoretically mean vaccum capacity generated is a function of engine rpms)

Dont miss the disclaimer - "Depress the brake pedal as strongly as you need to"

[TheCamShaft]

Originally Posted by purohitanuj

Dont miss the disclaimer - "Depress the brake pedal as strongly as you need to"

No Kidding, they really tried to cover their base well with that disclaimer , knowing that will anyway be done by the driver to stop the vehicle