Boost drops off to 11psi from 15psi.

[1993TalonTsiAWD]

Ok I have a 1990 GSX AWD with these mods

AMS short block 8.5:1
stock exhaust (yes next mod)
evo gt turbo (no flaming)
MBC Hallan spelling?? not sure how to spell the brand
evo exhaust manifold
ARP's metal head gasket
boost gage (of course)
stock intake (working on a evo mas swap)

Thats about it. Now for the problem

If I set it at 15psi it bleeds to 11psi, not sure whats causing this. I have searched, but no one had my setup. I don't know what RPM they bleed off. Tach's not working until I get a 90 ECU or 91+ power transistor. I thought maybe it was my exhaust, but I took it off at the down pipe, and it didn't help much, felt better, but still fell to 11psi. I do know it has a 34mm flapper on the WG and I'm wondering if that may be blowing open. Not sure yet. Also I know that it's still the stock 1g O2 housing, but I still think I should be able to hold 15psi on it. The timing seems fine, it only has 500miles on new short block. I just need to figure this bug out. It may even be a boost leak, but not likely, because I sure would think AMS would check for that, if not I wouldn't be to happy with them. Other than this, it's runny good, no knock, except for a little at 2500 (10 counts) AMS says it's because of the vibes the engine causes when it has the balance shafts removed.

Anyway can someone please help.

PS I still have the cat off, It was clogged, right now it's pretty loud though.
Don't worry it will be fixed tomarrow, it just was a test to see if I could hold 15psi and yes I have a upgraded pump (190)

thanks guys Derek

 

[oldman]

1. Ask if AMS had performed a leak test. If so, at what psi and for how long was it able to hold it?

2. At what rpm does the boost fall off? It's possible that you actually set the boost at 11psi and it spiked to 15psi instead of what you think the system is doing, set to 15psi and drops to 11psi.

I tend to think it's a boost leak problem. Even if AMS claims that they pressure tested it, I would still do one just to be sure.

 

[1993TalonTsiAWD]

I will do a boost leak test tomarrow. I have done many of them. It may be a spike, but I will know more tomarrow.

thanks Derek

 

[My96AWD]

subscribing. as mine is doing the same thing. it stays at 15 till about 5000 or 5500 then drops to 10. basic mods 16g and external. did it with a 14b also. has bad shaft seals but thats the only leak. internal wg holds fine. so im assuming its the tial wg. also the lowest i can set it at is 15 when i have a 10 pd spring in it.

 

[1993TalonTsiAWD]

Well heres a update.

We worked on it for about 10hours today.

First we did a boost leak. Found one at the TB, a bolt was missing (not to happy about that), also another leak was the PVC valve. Fixed those and still only holds 10psi or lower at WOT, it holds over 15psi when pressure tested.

So after a few hours messing with that, we decide to switch were the boost controller was tapped into from the waste gate to the bov. Went for a run other than a higher vacuum at idle nothing changed.

So after a few more tests we decided to swap out boost controllers. After that we did manage to hold 15psi dropping to 14psi, but it still didn't pull like it should. At this point I'm very stumped. Keep in mind it's stock exhaust, except for no cat.

So I did find part of the problem, but now I need to find out why it won't pull as hard as it should. It doesn't give that put you in your seat power.

My friends 14b at 15psi pulls harder, WAY harder than mine at 15psi and I have a EVO 16g.

thanks Derek

 

[1993TalonTsiAWD]

It's fixed for now, holds 16 drops to 13psi (because of stock exhaust). The MBC was installed backwords. Fixed now and pulls hard. Will pull harder when I get the exhaust done.

Derek

 

[1GTalonTSI]

That is exactly the problem I was having with my 92 TSI, it would go from 14 to 11...at this point everything is stock except the cut aircan... Sometimes it would boost hard and other times it would act like a NT 4 Cyl... My car had a 14b that came with the JDM motor I had installed... thanks for the upate on your fix.