FAST ???s

[PSIED 6 BANGER]

I am showing 14-15 psi on my gauge, but kpa on the fast b to b system after I run is showing 200 kpa????? and I know I am not at 29 psi because my bleed valve is closed. Do I have a bad sensor or what
Also what should my air fuel read or all of the junk for that matter.

HELP :biggrin:

 

[norbs]

Well thats about right, 200 kpa is 15 psi about, 314 kpa is about 30 psi, and atmospheric or 0 boost is about 100kpa. You should be about 11.5-7 a/f about.

 

[Craig Smith]

The FAST reads absolute pressure, which is one atmosphere off of gauge pressure. Everything is normal, nothing to be concerned about.

 

[sc68z28]

I'm also in Riverside Ca. My FAST reads 200 kPa @ 16 psi.

With the engine off, mine reads atmosphere @ 91 kPa. I assume thats due to appox 1300' elevation of the Canyon Crest area. At sea level it would probably be closer to 100.

Bill.

 

[PSIED 6 BANGER]

I looked it up on the net and it showed 103 kpa was 14.5 psi. But this has to do weather and elevation?
Im new to fast, can you tell
also Im in woodcrest

 

[JDEstill]

You need to know the difference between *absolute* pressure and *gauge* pressure.

Absolute pressure starts with a perfect vacuum as the zero point, and then starts going up.

Gauge pressure starts with the open air around you as the zero point, and then goes up and down from there.

A normal gauge reads zero when open to the outside air. You hook it up to an engine to read the pressure in the intake manifold and it reads vacuum at idle and boost at WOT.

An absolute pressure gauge does not act like that, it would reads positive numbers from idle all the way from idle to full boogie, because it is starting from a zero point of total vacuum. You'll never get a pure, total vacuum in the intake, and so that type of gauge will always read higher than zero.

Absolute pressure is about 14.7 psi (or 1 atmosphere, or 100 kPa) higher than gauge pressure. In other words, when a regular pressure gauge reads 0, an absolute pressure gauge reads about 100 kPa.

A MAP sensor is an absolute pressure gauge. When you have the key on, engine off, it should read about 100 kPa. Add 14.7 psi boost (or 100 kPa), and it should read 100+100 = 200 kPa. Which is what you are seeing.

Take your gauge pressure, add 100 kPa (or 14.7 psi) to that reading, and that is what your MAP sensor should be reporting.

Does that help?

John

 

[PSIED 6 BANGER]

THANKS for all the help guys and a/f should be 11.5 - 11.8 with wbo2 in down pipe about 8-9 inchs off of the turbo.

 

[norbs]

Well that depends, i would shoot for 11.0 a/f if you plan to use over 26 psi boost for some added cushion