Is it possible to have a vacuum leak only when the car is idling in gear with brakes applied?
Vacuum leak ?
- Thread starter jorton
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How do I check the brake booster for a leak?
Originally Posted By: jorton
How do I check the brake booster for a leak?
Easiest way is with a tach, and a pair of pliers. With car at idle, pinch closed the big vac line to the booster, see if RPM changes. Do the same thing again with the pedal down (don't pump it). If the vac leak is severe enough you can feel the difference without a tach.
How do I check the brake booster for a leak?
Easiest way is with a tach, and a pair of pliers. With car at idle, pinch closed the big vac line to the booster, see if RPM changes. Do the same thing again with the pedal down (don't pump it). If the vac leak is severe enough you can feel the difference without a tach.
I have used carb cleaner to find vacuum leaks. You spray it around where you suspect a leak and it will change the RPMS or even stall out the engine. Just be careful, I make sure the engine is cool so I don't spray it on hot parts and it ignites. I also keep fire extinguisher near by so if fire were to flare up I could put it out right away and there shouldn't be any damage since it would just be the carb cleaner burning off if you put the fire out right away.
I have found many vacuum leaks using this method without any problems, works good on intake leaks also. Cheap and easy to do. Otherwise the mityvac is the way to go.
I have found many vacuum leaks using this method without any problems, works good on intake leaks also. Cheap and easy to do. Otherwise the mityvac is the way to go.
You will always get SOME leakage from the brake booster with the brakes applied.
But realize that the brake lights have a significant load. This is especially noticeable at idle. This can cause a change in smoothness.
But realize that the brake lights have a significant load. This is especially noticeable at idle. This can cause a change in smoothness.
Originally Posted By: mechtech2
You will always get SOME leakage from the brake booster with the brakes applied.
But realize that the brake lights have a significant load. This is especially noticeable at idle. This can cause a change in smoothness.
First I shall do the booster vacuum line pinch test with and without brake light light bulbs installed. I expect the brake lights are causing idle rpm's to fall.
You will always get SOME leakage from the brake booster with the brakes applied.
But realize that the brake lights have a significant load. This is especially noticeable at idle. This can cause a change in smoothness.
First I shall do the booster vacuum line pinch test with and without brake light light bulbs installed. I expect the brake lights are causing idle rpm's to fall.
Pinch with the brakes applied and not applied.
All may be well when not applied.
All may be well when not applied.
Originally Posted By: mechtech2
Pinch with the brakes applied and not applied.
All may be well when not applied.
I finished the the pinch test. Brake booster seems to be ok. Now I think the car shakes because hot idle speed is too slow. Alternator voltage tested 14.4 vdc, but according to Oreillys counter person output is bad.
1999 Mercury Tracer a/t(same car)
Do you know why hot idle speed does not pick up when air conditioning compressor is engaged?
Pinch with the brakes applied and not applied.
All may be well when not applied.
I finished the the pinch test. Brake booster seems to be ok. Now I think the car shakes because hot idle speed is too slow. Alternator voltage tested 14.4 vdc, but according to Oreillys counter person output is bad.
1999 Mercury Tracer a/t(same car)
Do you know why hot idle speed does not pick up when air conditioning compressor is engaged?
Originally Posted By: jorton
Is it possible to have a vacuum leak only when the car is idling in gear with brakes applied?
Make? Model? Year? Engine? Trim level?
It is possible to have such a vacuum leak in the booster.
Check this way: Engine running, get down with your head in the driver's footwell, then push the brake pedal hard, by hand, and hold it there. You'll probably hear an initial hiss from the region of the top of the pedal, but then no hissing after that. If hissing continues, then the booster is leaking. This sort of leak would manifest no matter what gear the transmission is in.
Is it possible to have a vacuum leak only when the car is idling in gear with brakes applied?
Make? Model? Year? Engine? Trim level?
It is possible to have such a vacuum leak in the booster.
Check this way: Engine running, get down with your head in the driver's footwell, then push the brake pedal hard, by hand, and hold it there. You'll probably hear an initial hiss from the region of the top of the pedal, but then no hissing after that. If hissing continues, then the booster is leaking. This sort of leak would manifest no matter what gear the transmission is in.
Originally Posted By: jorton
Originally Posted By: mechtech2
Pinch with the brakes applied and not applied.
All may be well when not applied.
I finished the the pinch test. Brake booster seems to be ok. Now I think the car shakes because hot idle speed is too slow. Alternator voltage tested 14.4 vdc, but according to Oreillys counter person output is bad.
1999 Mercury Tracer a/t(same car)
Do you know why hot idle speed does not pick up when air conditioning compressor is engaged?
OK... good so far.
Your idle should be automatically adjusted for hot/cold, and load [AC,lights, etc.]. it is not doing so. Clean the TB and idle air motor valve. [don't just to the air valve].
You may nee a new one.
Originally Posted By: mechtech2
Pinch with the brakes applied and not applied.
All may be well when not applied.
I finished the the pinch test. Brake booster seems to be ok. Now I think the car shakes because hot idle speed is too slow. Alternator voltage tested 14.4 vdc, but according to Oreillys counter person output is bad.
1999 Mercury Tracer a/t(same car)
Do you know why hot idle speed does not pick up when air conditioning compressor is engaged?
OK... good so far.
Your idle should be automatically adjusted for hot/cold, and load [AC,lights, etc.]. it is not doing so. Clean the TB and idle air motor valve. [don't just to the air valve].
You may nee a new one.
Thanks.
Have recently cleaned tb and IAV with carburetor cleaner spray and a rag.
Originally Posted By: mechtech2
Your idle should be automatically adjusted for hot/cold, and load [AC,lights, etc.]. it is not doing so.
I should have described it like this eleven months ago. Is it a mechanical problem or an electrical problem with the IAV?
Have recently cleaned tb and IAV with carburetor cleaner spray and a rag.
Originally Posted By: mechtech2
Your idle should be automatically adjusted for hot/cold, and load [AC,lights, etc.]. it is not doing so.
I should have described it like this eleven months ago. Is it a mechanical problem or an electrical problem with the IAV?
Tough to check an air valve. A simple resistance check will show an open circuit, though. Probably a 2-3 of Ohms is normal.
I am surprised a code is not thrown for the unstable idle. it may be a hidden code. Get a free check at an Auto Zone
I am surprised a code is not thrown for the unstable idle. it may be a hidden code. Get a free check at an Auto Zone
Tegger I'll check that next.
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