Just finished my knock sensor and harness install and now the brakes are all wonky.

Just finished my knock sensor and harness project and got everything put back together. Took it for the first test drive and the brakes are all wonky. I can barely press the pedal down and it will hardly stop the truck. I'm 99% sure it's a vacuum hose but I've gone over the hoses pretty good and can't find any that aren't connected. Does anyone have any idea what I'm overlooking? Or anyone have the 4.0 vacuum hose diagram?

 

Check the large hose from the master cylinder brake booster to your intake manifold.

 

I've gone out in the dark two more times to look at this damn thing and I'm still not seeing anything super obvious

 

Where the hose connects to the intake, pull the hose off to look closely at the hose barb, maybe it cracked when you removed it for your previous work.

Or, it’s possible something like the brake booster or it’s check valve decided to die unexpectedly.

 

You won't believe this but the issue was that a mud dauber wasp had made a nest in the end of the vacuum hose. I had just stuck it back on the hose barb without even looking. Blew it out good with compressed air and now the brakes are working perfect. Thank you for your information! I appreciate it!

 

Pull the hose off of the intake with it running and see if theres vacuum.

 

I did. What I didn't notice as I was putting everything back together was that a dirt dauber wasp had built a nest in the end of the hose an sealed it off with a plug of mud. I blew that out with an air hose and now the brakes are perfect. Can't believe I didn't see that. Guess I was too excited about having finished the job.