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[kapspi]

In my 87 Diplomat, at ignition a high pitched ringing starts and does not go away, like a set belt alarm. It's gotten worse over the years and is really loud now. Pressing on the gas can make it quieter, and sometimes will make it go away momentarily only to come back when letting up on the gas pedal.


How do I fix this? Does pressing the gas pedal pull a vacuum (ie do I look for a vacuum actuated switch or a rotten line)? Or is it something else?

[Dippy.org]

[DobaMark]

Vacuum changes as engine RPM changes. The first thing is going to be to try and pinpoint the noise, do you have any idea if it's coming from inside or outside of the passenger compartment?. Vacuum would be described as more of a whistle than ringing.
Vacuum is routed inside the car to control the heater and A/C. If this is the problem area, you'd hear the sound originating behind the dash, likely in the climate control area.
You could have a ringing noise originating from any spinning component like the air pump, water pump, alternator, etc.

[lsm360]

What Mark says is what I was thinking pretty much. I'd open hood and listen from outside car, and bring revs up from throttle linkage to see if you can tell if it's from underhood.

[kapspi]

The noise is originating inside the car, behind the dash.

[lsm360]

In that case I would do as Mark advised and check the connection on the back of the HVAC controls. The connector tends to dry out and crumble apart after time and they do have hard vacuum lines coming into them.


https://www.forfmjbodiesonly.com/classicmopar/threads/hvac-under-dash-vacuum-lines-question.7761/

[kapspi]

The connector was indeed rotted. Replaced with some hose. Climate control is working again. Still a little bit of whistling. It's coming form the violet line which heads to the engine bay. I think I've located the whistle. I can adjust/eliminate the whistle by squeezing on the hose that attaches the white thing to the violet line. What is that white thing? What does it do? Are new ones available?

[DTSNEO6]

The white device on the violet hose is a check valve. The violet hose connects to a black hose for engine vacuum. 3441609 i believe is the part number

[Ark]

Ha, yeah that rotted connector would have been my guess. You're usually best off rigging something up with rubber lines and a grab bag of nipples and adapters, original parts are getting harder to come by.

[kapspi]

Here is the whistle. I found a good used one. So much better. It was driving me crazy.