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GMWrencher, ASE Certified Technician
Category: GM
Satisfied Customers: 439
Experience:  100% GM Certified ASE Master Automobile Medium/Heavy Truck. Licensed State Auto Inspector
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gmc sonoma: engine wall..brake booster and i

Customer Question

I have a gmc sonoma highrider 4.3 v6, w engine 4wd. I recently put a rebuilt long block
in this truck and am having trouble getting it to run smooth. I found damaged vacuum lines at back of engine and am not sure where lines connect, there is a y connection at the trans and a 3 line vacuum plug on top of trans, i think the vacuum line from the y connection goes to the fire wall by the brake booster and i am not sure where the line
coming from the 3 line plug goes to. hopefully this will take care of my rough engine.
Is there a diagram showing these connections?
Submitted: 6 years ago.
Category: GM
Expert:  GMWrencher replied 6 years ago.

Hello, I will do my best to help answer your General Motors Vehicle questions.


The 3 vacuum line connector that runs down the right side of the transmission connects to the transfer case 4WD vacuum switch. It is located on the top of the transfer case. The switch has It has a locater pin so be sure you plug it in correctly as it will slide on 3 different ways.

Edited by GMWrencher on 1/24/2011 at 5:27 PM EST
Customer: replied 6 years ago.
That does'nt answer my question, I know that the three hose plug goes to the top of the transfer case but do not know where the other ends connect? Also does the hose from the y connection at the top of trans hook up at the t by the brake booster?
Expert:  GMWrencher replied 6 years ago.

3 tubes...One is a vent that is just loose at the back of the intake. One is vacuum supply to the switch the other is vacuum signal to the front drive axle actuator under the battery. Usually there will be a Y or T connection to attach the vacuum switch supply to.


This is the best diagram I can find for your application.



Customer: replied 6 years ago.
what about the secound part of question, does the hose from the y connector go to the t fitting next to the brake booster?
Expert:  GMWrencher replied 6 years ago.

Do you mean the "Y" that is from the top center of the transmission? Are you asking does this connect to the fitting near the brake booster?

Customer: replied 6 years ago.
Yes that is what i am asking, from the top of the trans to the t at booster.Also there is another vac line that looks like it should hook up some where under the ac unit because it had a rubber type plug on the end and looked like it should plug into some thing.
Expert:  GMWrencher replied 6 years ago.
No The only hose attached to your transmission is a Vent tube. It should have a Y at the top of the transmission. The Y attached to a steel pipe coming out of the top of the transmission, One end of the vent line runs up behind the intake for an upper vent, while the second end runs past the transfer case for a lower vent. Only 4WD vehicles have 2 vent positions due to the possibility of going off road and through high water. The upper end may have a cap that is designed to vent.

Edited by GMWrencher on 1/26/2011 at 11:01 PM EST
Customer: replied 6 years ago.
Can you tell me where all the vac lines go from the trans and from the transfer case?
I would like to know where the vac lines start and where they end up.
I think there is the three line plug from the switch and a couple more lines by thethe plug.,
I am not trying to be a pain in the ass but i don't want to chase these lines around.
Expert:  GMWrencher replied 6 years ago.

Again there are no vacuum lines from/to the transmission, those are only vents. The diagram I posted earlier is the only one I have available for the transfer case vacuum hoses. Its really not important where you pick up vacuum from as long as its a constant supply. The 4.3 had a few different configurations. Some would pick up vacuum at the right rear of the intake while others used a vacuum tube close to the pcv port. I don't have any other diagrams to be able to help with exact vacuum hose routing and location. The under hood label will have a general vacuum schematic for your application. I hope the label is still attached and is correct for your truck.