Hey everybody, I posted this already but somehow it got deleted.

Heres my problem. my car is a 1990 TII, Well, at WOT ill hit 9 PSI no problem, then at about 6000 RPM it starts to drop off, Steadily till 7000 where it stay at 4 until redline. The turbo was rebuilt less then 8000 miles ago. so i would doubt its that. I dont think its a vaccum leak cuase i pull 20 Inches of vaccum on an aftermarket guage( autometer, but none the less aftermarket). Someone suggested a faulty Air bypass valve. So i was thinking of replacing it with an aftermarket BOV. someone also suggested to check the wastegate. ANY suggestions or ideas are GRAETLY apperciated. Thanks

Jerry

 

I have the same problem!! I just got dyno'd today and the same thing occured. I would hit 8-9psi then at 6200rpm it fall on its face to 4psi
Turns out its the boost solenoid (stock boost controller) that is just crapping out (not the exact explanation). Im going with a greddy profec B soon to fix the wastegate from opening too soon. Hope this helps. Here's my dyno sheet.
-Seth

sethdyno

 

Does your boost drop off instantly? or does it go down gradually? mine drops from 9 to 4 within 1000 RPM from 6000-7000. how would the the greddy profec B solve the problem? Couldnt i just disable the stock boost seliniod? and use a manual boost controller. Thanks

Oh by the way its me Fox4Life, Im just over my buddies house right now.

Jerry

 

This is what I think you should do.... Did you buy an MBC yet?

 

I guess thats worth a shot. I've seen tests though and the MBC isnt very responsive and reacts slowly to spikes. Thats why I was just gonna get something I know works well in the Profec B.
BTW: My boost falls off immediately.

 

hmmmm, Im just wondering if thats my problem or not. its worth a shot by i dunno. yea i ordered my MBC should be here today or tomarrow. but my boost problem is different then yours. you said yours falls off instantly, but mine goes down within 1000 RPM. how would i go about disabling that selenoid? Anyone else have any ideas? thanks

Jerry

 

Don't know about the solenoid.
Do you have an aftermarket BOV? If so, does your boost loss happen like that in all gears? If so, maybe the BOV is leaking. If it was a boost leak you would only see 4 all the time and wouldn't get to 8psi at 6k rpm. Try the MBC and please let me know how it turns out. Hell if I could avoid spending $300 I'd be happy.
Thanks.
-Seth

 

alright ill let you know the results. No i dont have an aftermarket BOV i have an DIY atmppheric. OSmeone suggested it could be a bad air bypass valve so i think im going to get a BOV very soon. thanks

Jerry

 

Take Freeds BOV assembly and try that.

 

hey its jerry

arnt the air bypass vlalves differnt for s4's?

 

mine drops from 10 - 6 or 7. stock turbo is too small.

MBC, 3" tid and exhaust.

 

I know the TID mod is good for about 1-1.5 psi. I still have the stock one, and have no idea of its condition and still suffered the loss. Atleast in my situation it didnt appear to be the turbo holding me back. I know the stock turbo is good for 230rwhp.

Scott89t2: where did you get your MBC at?

 

no it cant be the turbo, Its an s5 for crying out loud. and my buddy jimmyv13 hit 15 psi with an s4 turbo. Ok i could see dropping down to like 7-8 PSi MAYBE, but from 9-4???? come on, that a little extreme. Im thinking maybe the Air bypass valve. but thats just a guess. thats what i seems like, is the turbo is too small, but it gotta be bleeding boost off somewhere. either ABV or the WG. cheaper things first i suppose. Thanks guys

Jerry

 

well if something was leaking. it would also be leaking before 6k. it's not going to just drop off at 6k. somthing is getting maxed out. weither it's air thought the intake, TID, exhaust, stock ports, or turbo.

 

yea true, If somethings being maxed out, which is what it feels like. could it be a leak somewhere, i dont think it would be a vaccum leak cause im pullin 20 inches of vaccum, But could a boost leak be possible? If so where would i check? MAybe its the intake and TID, im not sure, i could try a new one, wouldnt hurt anything. i also doubt the exhaust would be the problem. Would it matter that i dont have a gasket between my DP and turbo? Im putting one on tomrrow but as of now i dont have one on. hmmm what exactly does the air bypass valve do? thanks

Jerry

 

might try cleaning the intercooler, or it could be a bad intake to engine gasket, or a bad upper intake to lower intake gasket.. just doublecheck that everything is tight.

 

Hey guys, Well i think it might be a little more serious then i first expected. Well i was coming home today, boosting pretty hard doing over 100 and i just happened to glance back and see smoke. needless to say i was really worried. It was thin black smoke. So im just guessing, but could this be a bad turbo seal? wouldnt that explain the funky boost problem. im in need of some advise here guys, thanks

Jerry

 

come on guys, someones got to have an idea.

 

Ever figure this out? I'm having the same problem, 9lbs until just over 6k and then it slowly drops down. its on an s5, and its just started to happen, so something mustve broken, and not just been maxed out. I dont have a gasket between the dp and turbo either (and i also have on nut missing on it) but i cant see how that would cause the boost to drop.

 

anyone? well, it not my air bypass valve or my TID. checked those yesterday.

 

Yeah what the hell does the air bypass valve do exactly?

The factory manual has this to say about the Air Bypass Valve: "Reduces sound of intake air from turbocharger relieved through air flow meter during deceleration"

That doesn't sound all that important to me? I was just gonna bypass it and see what happens, any coments please?

 

OK so the Air bypass valve is the BOV, that is good to know. But could someone clarify exaclty what a BOV does?

 

A bov vents the pressure from the turbo when the throttle is lifted off suddenly, this prevents a shockwave from the pressure bouncing back and damaging the turbo. Definitly dont bypass it. What the factory manual is saying is that it vents it to the intake rather than the atmosphere, this cuts down on noise, and lets the afm get the right reading.

Now has anyone had this problem with the boost bleeding off and fixed it? I'm about to get a manual boost controller, but I'd like to know for sure that it'll correct it.

 

Well I did figure out this whole turbo deal, First turbo so I'm still learning a bit. But as for the boost problem, I would mention the obvious stuff like hoses and such. Couldn't that cause your problem? Well I'm no expert, just though I would put in my 2 cents.

 

I drive a 1991 Turbo II, and I have the exact same problem. I have an HKS super sequential BOV working properly. My car smokes more than it should and my boost will drop from 10 lbs to 5 lbs within 1000 rpms. The reason for this is the old seals in the turbo, and the coolant and oil leak into the turbo and get burnt. Rebuild time for the turbo, or upgrade time. I'm personally going with a TO4B compressor wheel/housing from BNR supercars. Good luck!
-Nathan-