Vacuum sitting at 15

[diddy456]

Hey, my vacuum is sitting at 15 while I idle, but when I am in gear and left off the gas but keep it in gear it reads 20 like it should. I know my turbo is bad stock t25 it smokes. I am getting new turbo but could this be caused by anything other than the turbo? Piston rings, valves?

Let me know,
Shane

 

[MrBoxx]

Your vacuum readings sound pretty normal to me. The turbo shouldn't be affecting vacuum much at idle or coasting anyway, regardless if it's broken. Have you checked for shaft play/boost leaks yet?

 

[diddy456]

No, but I know the turbo has shaft play I can feel it(sorta grinding when I get on it). But I knew the turbo has had some shaft play for a while, I just never replaced it, will I hurt anything? And I think it has a leak but I am going to get it tested but just wanted to know if I had to test anything else like compression.

 

[MrBoxx]

Hmm... If the fins of the compressor wheel are rubbing against the housing, yes, that's definitely going to hurt something. Eventually, pieces will start breaking off and the play in the bearings will get worse, allowing more oil out. Replace the turbo as soon as you can.

You say the vac goes down to 20 in/Hg when you're in gear and off the gas, but what does it read just cruising in gear, say at 3k rpm? It should go down a bit when coasting in gear, since the turbo isn't pushing anything at all. I'm trying to remember what my T25 did right before it died. Seems to me, vacuum was normal, but boost kept decreasing until it wouldn't boost above 0. The decrease happened over a period of about three days, so if you notice your boost starting to drop from where you have it set or where it normally maxes out at, that's your clue that you don't have much time left. Hope this helps a bit and let us know if you get a new turbo.

 

[iiiwildfireiii]

My readings are almost identical to yours. ~15 in in idle, put into gear its ~20. While coasting I'll hit ~25 to 30. Turbo shouldn't affect it. I just went from a T-25 to a T04B V-trim. Same Vac/Boost settings. Dun worry about it, just get that bad turbo taken care of ASAP.

 

[TJGoSurf]

^ What they said is correct, I'll give you some reasoning now.

Turbo pushes air in, all n/a engines suck air in. So while you're coasting with no throttle being pushed in your engine is just sucking air in like it should. Completely normal. Believe it or not alot of n/a V8 guys use a vaccum gauge to measure how much their engine is sucking in.

 

[diddy456]

^ What they said is correct, I'll give you some reasoning now.

Turbo pushes air in, all n/a engines suck air in. So while you're coasting with no throttle being pushed in your engine is just sucking air in like it should. Completely normal. Believe it or not alot of n/a V8 guys use a vaccum gauge to measure how much their engine is sucking in.

SO its like at my first question, if the vacuum used to be at 20 with no throttle, and now it sits at 15 wouldn't there be something wrong with my engine sucking air like it should?

 

[flinguist]

Sounds like you might have a vacuum leak somewhere. My car idled with 20" of vacuum, before I stared modding it. I've done a lot to it (check my profile), and it still idles at 20". You should check all your vacuum lines, make sure there all connected correctly, and the tubing isn't cracked. However, if the car is running ok, I wouldn't worry too much.