[cosmos]

Originally Posted by download2live

I fail to understand how such an issue has got so little exposure on this forum. This thread is yet to go into second page !!!

What is Tata doing?? Just shrugging the shoulders???
Depressing the clutch totally before applying brake is not a recommended way. Will lead to premature brake pad wear. Also engine braking gives a smaller braking distance.

Thats exactly what the TATA are up to. I think it would have bothered them if it was an issue with their diesel vehicles as they comprise the majority of their sales. Both me and another fellow BHPian have got same kind of response from the showroom guys.

[cosmos]

Originally Posted by humyum

All I am trying to say is that AC and Braking have no connection at all as nothing is connected.

Sir, but this problem surfaces only when AC is ON. Never have I experienced it when AC is OFF for my 20000kms of driving in this vehicle. Logically AC should load the engine and should not have an impact on any other mechanisms in the vehicle.
Strange but this is true. TATA people never even bother to do anything. I'm complaining during every service.

[Sutripta]

Hi,
Not conversant with the Safire system, so exercise discretion.

With AC on, idling rpm goes up => less vacuum + engine trying to run the car at a higher speed.

I think it is a mix of two problems: vacuum leak, and poor ecu programming.
I feel the check valve in the vacuum line is leaking. Try this experiment: Start the car, idle it, and listen for hissing (= leakage) at the pipe connecting booster to manifold. Then press the brakes and get an idea of the feel. Now switch of the engine, wait approx 15 secs, and press the brakes again. If the brakes are now significantly harder, you have a vacuum leak.

What is the road speed in 2nd gear at AC idling speed?

ECU: Conjecture- when AC is on, on the overrun, fuel supply is not being shut off. And as it dips below its AC idling rpm, the closed loop nature of the system keeps on opening the throttle, increasing the engine power, and reducing the vacuum, both having a detrimental effect on braking. At this stage, see what happens if you knock it into neutral, and into first.

Regards
Sutripta

[jeeva]

I don't know how about the Indica Vista Saffire, but does the AC compressor and the Alternator run on the same belt?
If so, it might be something to do with badly designed pulley/mounting brackets/belt which probably fiddles with the belt tension when the AC is switched on, thereby making the vacuum pump unable to churn out sufficient pumping.

[rajeev k]

In Alto, during switching ON or OFF of AC while braking makes a change in pedal pressure could be felt. This I have experienced an many an Alto.

[dhanushs]

Originally Posted by humyum

An Ecu has got nothing to do with Hydraulics in the Brake lines. There is no provision to sense this.

Secondly I fail to understand what does AC have to do with 'braking' ? Even when the AC is running, it is sucking out engine power from the pully to the AC compressor and there is no vaccume pressure from the Engine required for the AC.

Even like someone said if the idling RPM is not going up by 100 or so rpms when the AC is switched on, that should not be a problem as the brake booster would be anyway fill itself with vaccume when the AC is not switched on and the RPM is same.

All I am trying to say is that AC and Braking have no connection at all as nothing is connected.

AC and Braking does have a connection. I'll explain.

Its the engine that delivers energy for the vacuum pump to churn out sufficient pumping and therefore maintain pressure along the lines.

When the AC is switched on, it sucks out a major portion of power from the engine, which the ECU should sense, and increase the fuel supply to cope up with the power/torque requirements.

In this case, when the engine is idling, the ECU might not be supplying enough fuel to the engine to cope up with the power/torque requirements and that includes power for the vacuum pump. And hence the hard pedal.

I'm quite sure that if, one could maintain revvs at 2k or more the pressure will be restored along the lines, and brakes more effective. Safire owners, next time, try to maintain revvs at or above 2k atleast for a minute or two and approach a signal or a hump, and lets see if the problem persists.

Its just like a high power ICE reducing the FE. For a novice, it would sound absurd.

[sureshkishore]

Originally Posted by jeeva

I pulley/mounting brackets/belt which probably fiddles with the belt tension when the AC is switched on, thereby making the vacuum pump unable to churn out sufficient pumping.

Originally Posted by dhanushs

AC and Braking does have a connection. I'll explain.

Its the engine that delivers energy for the vacuum pump to churn out sufficient pumping and therefore maintain pressure along the lines.

Dont think cars have vaccum pumps for brake. The Vaccum for the booster is drawn from the Inlet manifold.

Car engines normally should produce more than enough vaccum for the booster even at idling rpm of lets say 800rpm. More over the vaccum booster should hold enough vaccum for atleast one complete brake action even if the engine is off. If not the booster is leaking.

The problem in the vista case I feel is that when the ac is on the idle rpm is increased significantly lets say from 800 to 1100rpm and at that rpm engine produces enough torque (Unlike many other cars) to propel the car forward in second gear even without any acceleration.
So when you apply brakes you are working against the cars momentum and also the engine torque. Hence the feeling of ineffective brakes.

So, it makes sense in traffic conditions to depress clutch while braking.

The only solution is to reduce idling rpm with a/c to 800-850 rpm. Which requires ECU reprogramming.

[dhanushs]

Originally Posted by sureshkishore

Car engines normally should produce more than enough vaccum for the booster even at idling rpm of lets say 800rpm. More over the vaccum booster should hold enough vaccum for atleast one complete brake action even if the engine is off. If not the booster is leaking.

Usually true. but, the topic starter has specifically mentioned about brake pedal getting hard, and the only way for this to happen is decrease in pressure.

Originally Posted by sureshkishore

The problem in the vista case I feel is that when the ac is on the idle rpm is increased significantly lets say from 800 to 1100rpm and at that rpm engine produces enough torque (Unlike many other cars) to propel the car forward in second gear even without any acceleration.
So when you apply brakes you are working against the cars momentum and also the engine torque. Hence the feeling of ineffective brakes.

Safire being a petrol, would it have enough torque to pull the car against brakes at 1000 rpm in 2nd gear?. Also, imagine a situation,when you are at crawling speeds in 2nd gear. Depressing the clutch only increases the rpm, and not decrease it. May be Topic Starter can confirm.

[Abes]

I had this problem in M800 after AC was fitted. The service center guy told that this was due to a vaccum switch, the RPM being kept high to avoid engine stalling & provide enough power to compressor, and the lack of power brakes.

The solution given were to upgrade to power brakes, or dipress the clutch / turn off AC while braking to stop. I didnt upgrade the brake & was doing the second "solution".

But it did cause an accident; rear ended a jeep in a panic braking situation, when I didnt get the 'time' or pressence of mind to do anything other than applying the brakes.

There was no ECU in M800, I guess. And in vista's case, there is power assist for the brakes. Any guesses?

[mohandas]

^^^^
I wish vista was sold in the US. It would have been a real fun then. Mr. Obama would force Tata to sell his Ferrari CAlifornia to compensate the victims like you.

[humyum]

Originally Posted by dhanushs

Usually true. but, the topic starter has specifically mentioned about brake pedal getting hard, and the only way for this to happen is decrease in pressure.



Safire being a petrol, would it have enough torque to pull the car against brakes at 1000 rpm in 2nd gear?. Also, imagine a situation,when you are at crawling speeds in 2nd gear. Depressing the clutch only increases the rpm, and not decrease it. May be Topic Starter can confirm.

If the Zen MPFI can have the propulsion power to push the car forward with the ac on in 2nd gear in traffic, i am sure the Indica engines can do the same.

Originally Posted by sureshkishore

Dont think cars have vaccum pumps for brake. The Vaccum for the booster is drawn from the Inlet manifold.

Car engines normally should produce more than enough vaccum for the booster even at idling rpm of lets say 800rpm. More over the vaccum booster should hold enough vaccum for atleast one complete brake action even if the engine is off. If not the booster is leaking.

The problem in the vista case I feel is that when the ac is on the idle rpm is increased significantly lets say from 800 to 1100rpm and at that rpm engine produces enough torque (Unlike many other cars) to propel the car forward in second gear even without any acceleration.
So when you apply brakes you are working against the cars momentum and also the engine torque. Hence the feeling of ineffective brakes.

So, it makes sense in traffic conditions to depress clutch while braking.


The only solution is to reduce idling rpm with a/c to 800-850 rpm. Which requires ECU reprogramming.

Seems like the most probable scenario. Brake booster are run by vaccum from the manifold and there is no vaccum pump in the Indica petrol atleast.

A Swift diesel also 'seems' to have weak brakes in traffic because of its tendency to propel the car forward to stop it from stalling.

This engine braking thing has been pushed over the top. It's good to engine brake at high speeds but at 30's and 60's speed, it hardly makes a difference.

[supercars]

I have one idea.

My knowledge has been increasing reading about other people's problems.

I also felt that there is a connection between my Music System and the Engine.

I think that anybody who is having this braking problem should try to keep the AC at the lowest setting possible.
Please write here if my idea worked.

I also have another weird idea though you will have to find out how much another ECU(Non-Tata) would cost.

[Abes]

There is an old thread by high_octane titled: Indica Vista saffire brake problem when AC is on

[cosmos]

Originally Posted by Sutripta

Hi,
What is the road speed in 2nd gear at AC idling speed?

Hi Sutripta,

The problem is prominent at lower rpm in 2nd gear.

Originally Posted by dhanushs

I'm quite sure that if, one could maintain revvs at 2k or more the pressure will be restored along the lines, and brakes more effective. Safire owners, next time, try to maintain revvs at or above 2k atleast for a minute or two and approach a signal or a hump, and lets see if the problem persists.

Hi dhanushs,

Keeping the engine on boil does help. The vacuum is intact. In 2nd gear and at lower rpms there is severe problem.

Originally Posted by dhanushs

Safire being a petrol, would it have enough torque to pull the car against brakes at 1000 rpm in 2nd gear?. Also, imagine a situation,when you are at crawling speeds in 2nd gear. Depressing the clutch only increases the rpm, and not decrease it. May be Topic Starter can confirm.

I'm confirming. When you slow down by taking your foot off throttle, the engine rpm refuses to reduce. It stays where it is! The car keeps pulling without throttle or clutch being pressed and brake pedal is very very hard.

But if engine rpm is above 2k, the brake is normal and I'm able to stop. Re-iterating, the problem persists only at low speed and rpm.

[cosmos]

Hi Guys,

We have discussed about the problem. Some of you have given solutions. Can somebody sum up the feasible solutions for me? Someone told about bleeding brakes, re-mapping ecu and even getting a new ecu. How many of these are feasible?

Car is only 13 months old. Warranty would be an issue in case I do something.

I can think of two ways:

1. Get in touch with someone higher up in TATA and ask them to find a solution.
2. Get it done myself from some other service station who know what they're doing(forget warranty).

Which do you think is a better way to go?