Finding The Vacuum Leak on a GMC Syclone & Typhoon

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One of the most common issues that owners face with their aging trucks is vacuum leaks. Even the smallest crack in a line can take a healthy truck and make it run like garbage. Bye-bye Mr. Mustang as he pulls away from you at the light.

If you have never changed out your original vacuum lines (you should, and we'll save that for another article) and suspect that your truck's lack of go-power is due to a vacuum leak, here is a simple method to check your system and isolate any issues.

  • Clamp or glue (clamp is quicker and easier)
  • Old bicycle tube - dont plan to reuse it on your bike again
  • Air compressor
  • Hose clamp

Vacuum leaks can cause:

  • Unstable boost levels (or lack of boost completely)
  • Idle issues
  • EGR issues
  • HVAC issues
  • Hesitation or "missing" while in throttle

Testing the Vacuum System


Take your bicycle tube and cut it about 4 inches on each side of air inlet. Glue or clamp one end only to seal it off.

Image 407 from Finding the Vacuum Leak on a GMC Syclone & Typhoon

Attach the open end of the bicycle tube to the end of CAC and clamp with large hose clamp.

Image 410 from Finding the Vacuum Leak on a GMC Syclone & Typhoon

With your compressor, fill tube with air and listen for leaks. You can also have water in a spray bottle near to help find leaks (lightly spray any suspect areas with water and look for bubbles from escaping air). You can also blow smoke in the area of leak and it will also show where leak is.


Replace any hoses or fittings that are leaking.


Go find that Mustang and reclaim your manhood and the namesake of the GMC Syclone & Typhoon.

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