I just noticed this while looking at a picture of mine i took to pu in another post. See that vacuum line with the check valve in it circled. The single line comes off the back of the TB, then where it splits, one goes to the MAP sensor and the other goes over to the vacuum ball. That means the line going to the map sensor is "checked" and is never allowed to fluctuate with manifold pressure and give the MAP sensor a correct reading! OMG! Ive been running this for 10 years. Ive personally tuned the car, and it runs ok, but god! i wonder what it will do when i make it right, i might have to retune! Am i thinking correctly here?

I put all that stuff together when i put the motor in almost 10 yrs ago, and when i did it i really didnt understand all that stuff. I cant beleive i did that. Now when moving the cooling bypass lines it opened up some space and i saw that in the picture.

This is all being said as long as the check valve is still working.

 

The "check" keeps the vacuum from escaping the ball - everything on that line gets vacuum - but the "ball side" of the check valve won't let the vacuum "escape" back to the MAP sensor or the intake, if that makes sense.

If you pull off the MAP line, no noise. If you pull off the ball line, you'll here a hiss (air entering the ball).

 

I've learned alot about vacuum systems lately due to my F150 using a sort of complex vacuum system for the automatic 4x4 hubs. But what you see here is the map sensor on the same side of the check valve as the vacuum ball, which means the engine creates vacuum which builds and gets "checked" on one side of the check valve, this vacuum now doesnt fluctuate with engine RPM and load. Unless there is a leak or its used and drops below the engine vacuum which would then replenish it.

That being said, since the MAP sensor is supposed to read the fluctuation in the vacuum due to RPM and load to tell the computer what to do, it cant because its always going to see the highest vacuum possible because its locked, or "checked" behind the check vavle. Does that make sense? It does in my mind.

So what i need to do is connect that line to the vacuum line coming off the TB before hte check valve.

Wow this is going to change everything ive been tuning this engine for over the past several years.

EDIT:

Now that i look at this pic again, i might have jumped the gun, ill have to look at it in person after work. See the vac line underlined in blue, i dont know where that comes from or goes to, so i might have it right, but like i said ill have to check and get back to ya.



So what would the MAP sensor always having a high vacuum reading do to the engine throughout the RPM range. Make it run lean, or rich, or too advanced or too retarded. im just like beside myself right now.

 

High vacuum (low pressure), usually has more timing and less fuel. Unless the ECM sees it as an error and goes n-alpha.

Pull the line off the MAP and listen for a hiss, if so then it is as you first mentioned.

Should also run the MAP to the center port on the back of the TBI by itself. Nothing else should be on that line. This is so the manifold pressure variations are rapidly seen by the MAP sensor.

RBob.

{edit: the line underlined in blue is most likely going to the MAP sensor. The one off the check/T is most likely going to the HVAC controls.}

 

That's what I was thinking too after more thought. The blue line should run to MAP, the other should go to heater controls.

 

Ill check it out

 

Ok, everything is fine, false alarm. Everything is where it needs to be.