Vacuum leak and lean running?

Tiny
PAUL MENDENHALL
  • MEMBER
  • 2003 FORD E-SERIES VAN
  • 5.4L
  • V8
  • 2WD
  • 279,000 MILES
I have a 2003 e350 that has a vacuum leak and lean running issues. Codes show cylinders 3, 5, 8 misfire and running lean. My first step (I believe) is to find the leak. But I can't find a complete vacuum diagram to find and repair the leaks. I've replaced the spark plugs and coils. How do I best search for the leaks?
Saturday, September 27th, 2025 AT 9:13 AM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
Here is a video that can show you how to find the leak, also I know there is a large vacuum hose at the rear of the intake that is difficult to get to so check that first, also check the PCV hose as well.

https://www.youtube.com/watch?v=LRKWV4Are5c&t

and

https://www.youtube.com/watch?v=xN5pcM-5bso

both of these videos show different techniques, that both do a good job finding vacuum leaks.
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Sunday, September 28th, 2025 AT 11:04 AM

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