omniserv

Hello,

Still trying to figure out all the little problems with my new Z. It's a 1987 2+2. Besides the other problems I 've ask about on here I also have a strange vacuum noise coming from under the dash. The car has a digital heat control.

It's a vacuum sound that goes on and off like every 1 to 2 seconds when the heater controls are set to Econ and 75 deg. or so.

I removed the lower dash covers to see what I could find and discovered a few things about the system. I found 2 temp. probes in ducts that run out of the blower/control box on the drivers side. Also a air solenoid bank. When I unplugged the probes and removed the ducts so I could look inside the box the cycling on and off started right away. I could see what was happing is that disconnecting one of the probes cause one of the air solenoids in the bank the go on and off in a continues loop, just like it does sometimes while driving down the road. Inside the heater box I could see one of the deflector flaps going up and down with the sound.

What I don't know is if there are more than 2 temp. probes. If there is maybe one of the other probes is bad. I know the 2 probes I found are good because I swapped them as a test.

Has anyone else had a problem like this.

Thanks

Chris

AZ-ZBum

sounds like a vacuum leak. start replacing hoses in the engine bay.

omniserv

I'm 99% sure it's not a leak. The noise is one of the valves going on the off.

Just did nother test on it and it only makes that sound when the it's not set to defrost.

AZ-ZBum

Once again: You have a vacuum leak. Start by replacing the hoses in the engine bay. If that doesn't solve the problem, replace the $90 solenoid bank. But 30 feet of vacuum line costing $10 sounds like a simpler and cheaper approach to solving this problem. Doesn't it?

omniserv

I'll check and/or replace the vacuum lines. But my thinking is it's not a leak in a line because the valve is being powered on and off. I guess if a line were leaking that runs to a actuator and thus not moving a flap than it could be one of the lines under the dash.

So AZ-Zbum have you had this happen? just wondering

Chris

AZ-ZBum

Yes. It's a very common problem. Almost everyone has it at one point or another. Most of the time, replacing the vacuum lines in the engine bay fixes the problem.

The issue is the valves in the car require a certain vacuum to operate. If they don't have this amount of vacuum, they will flap around. You might get clicking or popping sounds. You might get hot air blowing out your dash vents. etc.

omniserv

Thanks for the better explantion. that does make since. Tomorrow I'll do a 100% inspection on the hoses. I hope that's all it is.

omniserv

Ok, I presure tested all of the vacuum lines under the hood and all of them are ok. In fact the line going through the dash still had vacuum in it 20mins after I shut the car off. So I know it good. Guess one of the lines under the dash is hosed. Or something else.

omniserv

Ok After spending most of the eve. under the dash. I now know for sure there's a leak in the vacuum lines. The 3rd valve from the back, when it's on I here the leak. The problem is I can not follow all the lines.

Does anyone have a diagram of where each line goes for a 1987. The book I have is for a 84 model and does not show the auto system in it at all.

Thanks

Chris

AZ-ZBum

http://www.carfiche.com

entropy31

just a hint, when doing vaccum lines, do one at a time so you dont get mixed up. i know, simple thing, but simple things are the most likely to be overlooked.