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I had a coolant leak on the crossover pipe on my 5.4 triton in my 2003 f150. Took intake manifold off to fix and discovered it was broke. Bought new intake manifold from Rock Auto. Cross checked everything and it said it would work. Put new parts on and hooked everything back up correctly and it tries to start but only with throttle wide open and it backfires through the throttle body. The air mix box on the bottom of the intake is smaller than the original but not by much. I wouldn’t think this would matter. Some insight would be helpful. Thanks.
The big port on the back of the manifold is open to atmosphere?
Sounds like you have a vacuum leak if it is backfiring through the intake
The hose has a tendency to collapse and tear
it would have to be loose enough to be whistling indicating a vacuum leak
The tee's colapsing and rupturing is what you are looking for and any other vacuum leak, like the power brake booster port
I appreciate all the comments but it would be a lot easier to check for vacuum leaks if I could actually get it to start and stay running. Which I can’t.