Hello everybody. This past weekend I changed out my oil pressure sensor. This requires removal of the intake manifold. After replacing the sensor I put everything back together. The new sensor was working great, however, I noticed a hissing noise coming from the car. Well I checked all of the hoses and couldn't find one that is disconnected. So I've driven the car as is with the hissing noise. The car displays no codes and actually seems to run just fine.

Fast forward to this morning, 13 Sep. I start my car and had to turn on the defroster for the windshield. Well the A/C venting control did not respond to any position and is actually stuck in face&foot mode. So I've been reading in the service manual about the HVAC vacuum tank and it states the following, "Vacuum stored in the vacuum tank is prevented from bleeding back to its source during conditions of low engine manifold vacuum(acceleration, heavy load, etc.) by a check valve in the vacuum source line."

When I changed the oil pressure sensor I did not replace the intake manifold gaskets. Here is the $64K question. Would a leak from one of the intake manifold gaskets cause a condition of low engine manifold vacuum and therefore causing my problem with the A/C vents? Would this also cause a hissing noise but not really effect engine power/problems also?

Thanks for taking the time to read this and any help would be greatly appreciated.

Murnutz

 

Are you certain you plugged the small vacuum line back in on the back of the manifold? There are two lines...one to the brake and a very small one that controls all the vents and their direction. Seems logical if you defroster isn't working.

Mine cam off after manifold work too. Remove the PCV line and unplug the injectors on the passenger side. You can see and feel that very small line. It is literally as big as a black wire with a rubber fitting on the end that plugs to the back of the manifold.

 

Oh, and the gasket should be fine if no tears or damage. I reused mine without any issues.

 

Buckmaster,
I removed the PCV line and injectors and I could not find the "black wire" you speak of. Is it reachable without taking the manifold off? Do you happen to know of a diagram in the service manual that show this tube and connector? Thanks for the help.

 

Actually you don't need to remove the injectors......just the connectors. And that is only to be able to move the whole wire harness for more room to get your hand in there. With my problem, as soon as I removed the PCV line and the injector harness out of the way I could see and feel the very small black vacuum line with a "L" shaped rubber fitting that plugs into the back of the manifold sitting there. The vacuum line is literally as small as a black wire. It is very small in diameter. The line may have fallen down below the manifold, that's why you can't see it. If you can get your hand back there try and feel around. Again, it is very small.....but it shouldn't have fallen far if it did fall down a bit. A small mechanics mirror may help see it. I was able to do all of this from the passenger side. The small area (the connection on the manifold) the line plugs back into is on the passenger side...........damn....it is hard to describe typing..........

 

this is my bet
almost missed it myself when I did mine

 

You have been here since Aug 2001, and you dont know where the tech tips are?
I did a complete R&R of the oil sensor including pictures torque specs and things to be careful of, including the 1/8 black vacuum line that connects to the rear of the intake.. with special emphasis on this line because it is small and it controls your A/C climate control doors. This line is located on the passengers side of the intake.

 

Buck,
Thanks for the info. I'm going to take the manifold off again this weekend and look for the connector. Its kind of hard to find that connector with all the stuff in the way, plus it doesn't help that I can barely fit my hand back behind the manifold.

Evil,
I'm aware that there is a tech-tips section. I have the service manual and went by that. But the manual doesn't tell you the little things as described in your tech tip.

Murnutz