# Brake booster vacuum issues



## kalinga (Aug 12, 2010)

Hey ppl

i got a Sunny B14 JDM, found that there seem to be a leak in the Brake booster, since the paddle is stiff and as soon as the engine is off the paddle become really hard.

anyway the issue in hand is, i have notice reduce engine power. with the start.. once you pass 2nd gear issue is gone. 

can the leake in the Brake booster case this issue ?


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## LvR. (May 26, 2010)

IMO that is perfectly normal behavior of the booster - the first press on the pedal after engine switch-off will effectively consume the vacuum and you will be stuck with a plain direct mechanical link to the master cylinder - hence the really hard pedal.

As for the loss of power - way more detail needed on what you have discovered while investigating the issue while studying the FSM (stickies)


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## kalinga (Aug 12, 2010)

hey LvR..



LvR. said:


> IMO that is perfectly normal behavior of the booster - the first press on the pedal after engine switch-off will effectively consume the vacuum and you will be stuck with a plain direct mechanical link to the master cylinder - hence the really hard pedal.


what I'm saying is even when the engine is running after a press the peddle is hard for few seconds, and it improve over time. 

let says i switch off the engine with out pressing the peddle and then press is after few seconds, its hard.

i have already replace the vacuum line that include the valve. 

the master pump is fully replaced few months back. and the lines has been checked and bleeded for any air. pads are new. 

i feel the brake are not up to what they use to be. 

this is a non-ABS brake system.

so only thing i can think is the vacuum system. there are no fluid leaks or any thing else.



LvR. said:


> As for the loss of power - way more detail needed on what you have discovered while investigating the issue while studying the FSM (stickies)


TPS is at 0.5v at idle and 4.5v at full, MAF is around 1.3v at idle, 750rpm. 

fuel mixture shows as Rich. 

injectors, has been cleaned, including the throttle body, air cleaner and fuel filter, and the fuel pump is also checked for pressure. 

ATF oil is at the right level, only 20,000KM done on it. (new oil) (12427mil)

issue is like this, while the car is on stop, when it start to go, it slow a lag in response and feel that there is no power to go on. once it start going around 20~30km/h (30-40mph) since it get switch to the 2nd gear, no issues at all.

when i say lack of power, dont mean the car wont move at all, but its not like what it use to be.

also the catalytic converter and the exhaust system is checked as well.


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## LvR. (May 26, 2010)

> what I'm saying is even when the engine is running after a press the peddle is hard for few seconds, and it improve over time.


So I get from that, that the pedal feel only starts to normalize after a few actuations with the engine running at idle (max vacuum) - right?

Guess the proper suggestion would be to actually measure the engine vacuum at idle? - only then will you know if the lack of vacuum or booster is to blame.



> ssue is like this, while the car is on stop, when it start to go, it slow a lag in response and feel that there is no power to go on. once it start going around 20~30km/h (30-40mph) since it get switch to the 2nd gear, no issues at all.


In 1st gear? ............................ IMO there is no mechanism on the vehicle that can affect acceleration performance in this way (other than the gearbox and associated comps) ................... I suggest a compression test and post back all individual cylinder values here if there is nothing obvious wrt the FSM


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## kalinga (Aug 12, 2010)

LvR. said:


> Guess the proper suggestion would be to actually measure the engine vacuum at idle? - only then will you know if the lack of vacuum or booster is to blame.


how much of a psi should be there at idle ?



LvR. said:


> In 1st gear? ............................ IMO there is no mechanism on the vehicle that can affect acceleration performance in this way (other than the gearbox and associated comps) ................... I suggest a compression test and post back all individual cylinder values here if there is nothing obvious wrt the FSM


did a compression test and it was fine.

I'm no so sure about the A/T, i did try manually switching from 1st to 2nd, no improvements. 

just feel that the engine is lacking power. 

is there any way to check the HT power that goes to the plugs, maybe its not adiquite ?

my service guy told me that best to replace the distributer and check. but i got my droughts.


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## LvR. (May 26, 2010)

Replacing the distributor?! - guess its a test but wow at what cost?. I would rather first drop the car on a dyno and get a timing and fuel map - you will learn a lot more about the whole engine's condition from that exercise.


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## jdg (Aug 27, 2009)

What about 1st gear itself? Possible slippage? Torque Converter clutch possibly dragging (I know, I can't see it either...but check earlier posts...)


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## kalinga (Aug 12, 2010)

LvR. said:


> Replacing the distributor?! - guess its a test but wow at what cost?. I would rather first drop the car on a dyno and get a timing and fuel map - you will learn a lot more about the whole engine's condition from that exercise.


ah, oh boy I'm not in states, i live in Sri Lanka, finding a guy who understand about fuel maps and have a dyno... man i would love to see that but not that lucky. 

thats why im asking around here, so i can get a better understating from people with experience. 

the suggestion was given by the Nissan dealer/service center here. car was with them for almost 10 days and didn't do shit  excuse my French. 

re-com distributor would cost around $150 or so. but i don't like to take that chance.


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## kalinga (Aug 12, 2010)

jdgrotte said:


> What about 1st gear itself? Possible slippage? Torque Converter clutch possibly dragging (I know, I can't see it either...but check earlier posts...)


if there is slippage, the RPM's need to go hight right, but thats not happening. the engine take time to acceleration. the lag is there in the acceleration.


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## skeeter123 (Apr 30, 2010)

Have you checked the ignition timing? It has to be put into "timing mode", then set to 10 degrees... Check FSM for the procedure. My daughter had a friend "fix" hers, without knowing about this "timing mode", car lost all power from dead stop, but would seem to run OK once up to speed. Setting timing right made a huge difference in gas mileage, too.
Hope this helps.....


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## kalinga (Aug 12, 2010)

skeeter123 said:


> Have you checked the ignition timing? It has to be put into "timing mode", then set to 10 degrees... Check FSM for the procedure. My daughter had a friend "fix" hers, without knowing about this "timing mode", car lost all power from dead stop, but would seem to run OK once up to speed. Setting timing right made a huge difference in gas mileage, too.
> Hope this helps.....


guess this can be the issue, since the dealer saying i need to replace the distributor. the car was fully tuned by the dealer. maybe they missed this ?

i was thinking to check the HT cables to see if they are any good. 

plugs looks good, white and clean. that mean there is a good fuel mixture right ?

but the car is doing poorly on the gas mileage, anyway i would find out today since i have to do a emission check today for my registration renewal.


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## etepsnewo (Jul 5, 2008)

So . . . . what happened? How about an update?


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