nimravus01

Hi everyone! I think I messed something up... I loosened this cap and heard a vacuum sound like releasing pressure or sucking in; kind of like opening a bottle of soda pop the first time. Now the car feels lazy, like I'm not getting any boost.

What is this cap? What does this system do? Is it hurting the car to drive it before it gets fixed? Does a mechanic need to pull a vacuum to fix it, or, is there something I can do at home?

Thanks!

Dubduece

I believe thats the AST it seperates air from the coolant and you probably popped a vacumn line somewhere.

Sgtblue

iTrader: (16)

Yes, that is the AST (Air Separation Tank). Sounds complicated but really it's not. Just a place where air can be purged from the cooling system when the radiator is NOT the highest point in that system. Vacuum at that cap (and the other cap) when the engine is cold is perfectly normal...a good thing. If you bring the engine up to operating temp and let it cool down, removing that cap will release the vacuum again. But while you didn't "screw up" by removing it, it would have nothing directly to do with your sense that the engine is "lazy" and not getting boost.
Do you have a boost gauge?

nimravus01

Thanks for the clarification. I downloaded the factory service manual after I posted the origional question. I see what the cap does and how the system works now. As for the boost, I think it was all just in my head. I don't have a boost gauge. My car is actually all stock setup. I didn't have a camera to use at the time, so, I posted a pic I found on Google for reference purposes. Here's my car:

Thanks again for the reassurance. I'll be getting a lot more hands on with the car in the next year.

Gringo Grande

iTrader: (97)

Get an aluminum AST ASAP to replace the stock one...and a boost gauge. Welcome!

Sgtblue

iTrader: (16)

+1.
If it is all original, consider replacing the radiator with an all metal verson too. Like that plastic AST, with this many years and heat cycles the plastic end-tanks have a tendency to fail....sometimes catastrophically. Great time to flush and change out the coolant anyway.
Some other things that come to mind for a new owner of an ALL ORIGINAL FD is to install an aftermarket temp gauge. DO NOT rely on the factory gauge. It's not linear and if it ever moves from just below "half-way" it's usually too late. Search for more info on installing a temp gauge and where to put the sender.
Check to see if your pre-cat has been replaced by a downpipe. As unlikely as it might be, you want to get that changed out as well. It's been known to collapse and plug your main cat...which can also cost you an engine. Kind of a PITA job, but it's also a "performance modification" too.

nimravus01

Thanks for all the info! Well, it's not all original... the engine was replaced with a reman, the pre-cat was replaced with a down pipe, the radiator was replaced, and one of the turbos was replaced. All the hoses were scrapped and silicone hoses were fitted. I will see about the AST and an after market temp gauge.

GSP David

hope you get this resolved!