I have an odd question because I have an odd situation. I took my 89 GTA into my GM service department to replace two hard to reach heater hoses under the drivers side of the car that snake around the oil filter. When I drove home after work I noticed two things.
1) Now the AC and VENT functions only blow on defrost(and the vent flow was working when I drove it in to the service dept)
2) The Cruise is harder to "set up" and doesn't hold the speed well. It will for a bit then starts to drop off. I tap the gas and it kicks it back in for a bit but I never had ANY problems till I took it in. The tech that worked on the car swears he never touched any vacume lines, made a spot check and didn't see anything. Is there a shared source I might check? I will check it out myself on my day off Sunday but need a few suggestions as to what I should be looking for.

 

Most if not all GM cars, both the HVAC system and cruse control share the same vacuum source.

Locate the vacuum tank (ball) under one of the front fenders forward of the wheels.

Follow the vacuum line from the tank and it should "tee" off; one line will go to the cruise control servo, the other line will run along the fender back along the firewall and connect to the plenum.

Some where in the line that runs along the fender to the plenum, there should be another "tee." The tee'ed off line should run through the firewall to the HVAC controls. The plastic "tee" here is a one-way check valve.

The purpose of this valve is to hold vacuum in the lines running to the HVAC controls and cruise control during low vacuum conditions (moderate to high engine loads).

Isolate and check each of the vacuum line runs separately for leaks. Look for broken plastic vacuum hose connectors. Also, check to make sure that the check valve will hold vacuum in one direction - pull a vacuum on each nipple. One of them should hold vacuum.

 

Thanks for the heads up and that is exactly what I was trying to find out! One other question though: Do the TPI cars have the vacume ball in fender? My car is at home or I'd look but I swear I thought my 87 GTA didn't have it and I saw those vacume ball's on the V6 models when I went to the junkyard?

 

Pretty sure the accessory vacuum arrangement is not engine-specific... it's part of the "car", not the "engine". All of these cars have some sort of a vacuum canister; AFAIK starting in some particular year it became the ball thing and was used in all of them.

 

Thanks! I can't wait to get home and start looking!😀

 

Update: today I looked at all the vacuum lines and discovered a disconnected line on the passenger side. There was a vacuum tee with one open end and a vacuum leak. The thin, hard hose coming from the firewall came out. Thanks for pointing me in this direction or I'd have never found it. My service tech said he tried to reposition my ignition wires and used a zip tie on that tee which put so much pressure on it the line broke.