My friend has a 89 CRX with a B17 motor, we connected a vacuum gauge to the vacuum hose that connects to the map sensor and it's reading 0 psi at idle. Is this normal??

We then connected the gauge to the FPR vacuum source and it's reading fine (has vacuum during idle).

 

yes, that is perfectly normal. Your MAP runs off of vacuum which is normally measured in inches of mercury not pounds per square inch.

Now, I belive you folks connected the MAP hose to that big vaccum tube smack in the center of the throttle body, Right?
That is for the EVAP system and it only sees vacuum when the throttle is opened. No vacuum during idle.
So look to the right of that center tube and you should see another vacuum fitting. That's the one for the MAP sensor.

Hope that's it.

 

So inches of mercury must be a really really small reading that the gauge can't even read it? Because the gauge, which is actaully an electronic Greddy boost gauge, sees 0 PSI constantly.

 

Does the gauge show only positive pressure or does it go past 0 on the negative side and show vacuum?

 

Vacuum and Positive. It's a turbocharged motor b.t.w....

Also, when disconnecting that vacuum line to the map sensor, the car still idles fine.

 

I circled it in red. It's getting a 0 psi reading in idle:

 

Hmm..i dont know if there is vacuum there at idle, i have never really checked that. Spray some carb cleaner in there and see if its clogged ?

edit: i see the problem, u have your coolant reservoir in the wrong spot. j/p

 

seriously, those TB connections are crappy. ive noticed some very low vac readings from the nipples on the TB. so for future reference i would route ALL vac sources from the IM and T offf anything from those.

 

You will not see PSI out of there at idle.
It will always read zero PSI at idle.
You need a "vacuum" gauge.
Take the throttle body off and clean that passage with a needle and some carb cleaner.
That shuld fix the problem

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by The new Spaceballs &raquo;</TD></TR><TR><TD CLASS="quote">You will not see PSI out of there at idle.
It will always read zero PSI at idle.
You need a "vacuum" gauge.
Take the throttle body off and clean that passage with a needle and some carb cleaner.
That shuld fix the problem</TD></TR></TABLE>

The Greddy gauge that he has is a vacuum/boost gauge.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fourthgenhatchB17 &raquo;</TD></TR><TR><TD CLASS="quote">Hmm..i dont know if there is vacuum there at idle, i have never really checked that. Spray some carb cleaner in there and see if its clogged ?

edit: i see the problem, u have your coolant reservoir in the wrong spot. j/p</TD></TR></TABLE>

What I don't get is ... his car is turbocharged. If it is "clogged", wouldn't the pressure force all that gunk out?