Vacuum leak and lean running?

2003 FORD E-SERIES VAN

279,000 MILES • 5.4L • V8 • 2WD

PAUL MENDENHALL

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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?

Sep 27, 2025 at 9:13 AM

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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.

Sep 28, 2025 at 11:04 AM