This just started happening in my car yesterday. mods are downpipe, midpipe, catback,silicone hoses, fan mod and manual boost controller. Doing the turbo test third gear 11-7-11 boost pattern but when I shift to fourth and step on it 2-4 pds of boost and thats it? Let off the gas and get a vacuum for about 2-3 seconds then step on the gas car boosts normal???? is this a vacuum canister problem? can't find any boost leaks or vacuum for that matter. Any ideas?
Thanks
Dan

 

vacuum chamber is leaking

 

replace the check valve between the UIM and the firewall, it should correct your problem, if not then ur vacuum chamber probably is leaking and u can grab another one of those

 

vacuum chamber is the answer~~~

 

thank you gentlemen I will take a look at the vacuum chamber!!
Dan

 

Use a Mighty Vac and see if will hold vacuum. I guess you could also use a cheap test guage, monitor it while driving to see your max reading then see how long it holds.