HELP - Sucking noise behind the dog house...!!!
 

I have a weird air sucking noise that seem to be coming from behind the dog house. It's most noticeable during acceleration. The noise may have always been there from when I bought the van but now it has become louder and very annoying! I can hear it swithing on and off during accel/decel.

I thought it may have been the either the bypass or diverter valves in the thermactor system since they are both just behind the dog house. These valves both hold a vacuum okay so the diaphrams must be okay. I have not check that engine is supplying a vacuum - I guess I probably should check this.

Anyway, engine runs fine, pulls hard and is not throwing any codes. Anyone have any thoughts/checks/ideas on this condition before it drives me nuts?!

Paul
1995 E150 conversion 351 55K miles

I usually try spraying some carb cleaner at the gaskets and vacuum lines to look for a leak. If you hit one the engine will change rpms.

Is it fuel injected or carberated? On some engines with carbs, the carb can come loose from the mounting plate and cause a sucking noise. Have you seen a drop in fuel economy? Any transmission slippage? It could be a vacuum modulator, a worn out vacuum line, a bad vacuum pump, etc... I would need more info to be able to give any other ideas

It could also be a bad PCV valve.