Have recently developed "sucking"/vacuum type sound while accelerating past 3K RPM. It is transient and resolves on backing out of throttle or continuing upward past 3500. Any ideas? We used to have symptoms like this with ambulances (old days, 7.5L) and vacuum leaks. Appreciate any help

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Have you changed your air filter lately, check your air box for a opening....Dave

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1998 F-150, SC/Flairside, 4x2,4.6,auto,3.55s,nerf bars,cls 111 towing,bed liner w/mat,atlas polished wheels w/ 265 scorpions,all plastics guards/bug shields,air raid/k & n filter, superchipped, duals out the back corners, flow master 3 chamber, snug top lid, f-150 online sticker back window-honk if you see me!!! Fabtech 3 1/2 lift will be on by oct 1st...

San Antonio

 

Get a can of carb cleaner or Brakleen. Spray it all around the intake area and by all vacuum lines. I don't mean saturate it, just a light spray. If you hear your engine rpm change, then wherever your spraying at that moment is the leak. If nothing happens, chances are you have no vacuum leak.

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1997 F-150, Dark Toreador Red, Supercab, Flareside, 4X4 Off-Road, Chrome Grizzly Wrap Around Push Bar, and Lots of TLC!!

 

I have recently changed the filter and can not detect any obvious openings around the airbox. However, I will try the spray idea. Appreciate it

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Be careful with carb cleaner! Most of your rubber, plastic and painted parts won't respond very well to a dousing of the nasty stuff. I would use brake cleaner or maybe electric contact cleaner. Those are much milder and will accomplish the same goal.

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98 F-150 XLT 4X4 ORP Super Cab Short Bed, 4.6, Auto. Superchip, Gibson sing. cat-back, Airaid, 80/100w German head lamps. Needs one more door and a lot more power. I think I need to talk to Mr. Whipple.

 

Brake clean does not generally work for this purpose. It's usually non flamable. Plus, when I tried it, it made extremely noxious vapor come out the tail pipe (chlorine smell so stong it would choke you). Also, only spray downstream of the air meter. You may damage the meter if you spray the air box and there is a leak. Also, the throttle body has a coating and is labeled with a label that says not to use carb cleaner on it.