What is the normal vacuum pressure at intake manifold?
03-29-2007, 01:29 AM
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What is the normal vacuum pressure at intake manifold?
What is the correct or normal vacuum pressure at the top intake manifold?
My 96 readings are 13 inch Hg at idle, 15 inch Hg under 2000RPM, and 18 inch Hg over 2500RPM. The read-out are taken at both ports on the top manifold, one goes to the fuel pressure regulator and the other next to it with a plug. The read-out will jump from 13 to 15, then to 18 as engine speed increases.
A 13 at idle is too low. Normal reading should be 18-23. It may have a major vacuum leak or late ignition timing. What is the proper way to read the vacuum pressure? What are the reading should be?
gc
My 96 readings are 13 inch Hg at idle, 15 inch Hg under 2000RPM, and 18 inch Hg over 2500RPM. The read-out are taken at both ports on the top manifold, one goes to the fuel pressure regulator and the other next to it with a plug. The read-out will jump from 13 to 15, then to 18 as engine speed increases.
A 13 at idle is too low. Normal reading should be 18-23. It may have a major vacuum leak or late ignition timing. What is the proper way to read the vacuum pressure? What are the reading should be?
gc
11-19-2007, 08:51 AM
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What is the correct or normal vacuum pressure at the top intake manifold?
My 96 readings are 13 inch Hg at idle, 15 inch Hg under 2000RPM, and 18 inch Hg over 2500RPM. The read-out are taken at both ports on the top manifold, one goes to the fuel pressure regulator and the other next to it with a plug. The read-out will jump from 13 to 15, then to 18 as engine speed increases.
A 13 at idle is too low. Normal reading should be 18-23. It may have a major vacuum leak or late ignition timing. What is the proper way to read the vacuum pressure? What are the reading should be?
gc
My 96 readings are 13 inch Hg at idle, 15 inch Hg under 2000RPM, and 18 inch Hg over 2500RPM. The read-out are taken at both ports on the top manifold, one goes to the fuel pressure regulator and the other next to it with a plug. The read-out will jump from 13 to 15, then to 18 as engine speed increases.
A 13 at idle is too low. Normal reading should be 18-23. It may have a major vacuum leak or late ignition timing. What is the proper way to read the vacuum pressure? What are the reading should be?
gc
Somebody here ought to have the 993 specs or you should be able to find them somewhere on the web. The site I referenced may help with what the variations mean.
Pete
11-19-2007, 12:06 PM
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Thanks for the link. Very informative. Looks like I may have a problem.
Can anyone get a reading from the port on the top manifold, the one with a plug? TIA.
gc
Can anyone get a reading from the port on the top manifold, the one with a plug? TIA.
gc
11-19-2007, 12:35 PM
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I can try but I need to take a look if my vacuum guage is calibrated...its a cheapie and it just has the yellow-green-red type of scale.
I have never seen this information posted though...it would be interesting to see numbers are "proper".
I wonder if another Rennlister can swing by or you can meet and use your gauge on their engine, that way you eliminate calibration errors etc.
Cheers,
Mike
I have never seen this information posted though...it would be interesting to see numbers are "proper".
I wonder if another Rennlister can swing by or you can meet and use your gauge on their engine, that way you eliminate calibration errors etc.
Cheers,
Mike
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11-19-2007, 02:19 PM
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It is 15 to 16 inch Hg. Thanks Colin.
Can I assume regular ECU control engines have higher vacuum pressure because it is less efficient than Motec?
gc
Can I assume regular ECU control engines have higher vacuum pressure because it is less efficient than Motec?
gc
11-20-2007, 09:59 AM
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The vacuum recorded by an engine is purely as a result of the engine design rather than the engine management, however it is (in theory) possible to tune the engine to the same idle speed using less ignition timing and a more open idle control valve which could lead to a small difference.
