Hey guys,

Car: 1990 S5 TII

I'm pretty frustrated at this point, so I'm coming here to see if someone can help me fix my problem.

What happens:

I floor it, lets say from a 2000rpm roll in second gear. It pulls hard, the boost climbs quickly from 2 to 13. The RPM's continue to climb, and 5000 rpm comes up. Now's where the trouble starts.

Slowly, as the RPM's continue to raise from 5000rpm, the boost begins to drop from 13 psi (or whatever boost i'm running) to 5 psi. Once I hit redline, the boost holds strong at 5 psi. The power starts fading after 5000 rpm. Extremely frustrating.

I talked extensivly to RETed about this problem, and his solution hasn't worked thus far.

He told me to buy:

- Walbro 255lph Fuel Pump
- Greddy Profec-B Spec II

Both have been bought and installed, and neither have fixed the problem.

It is possible that I'm doing something wrong with programming the Profec-B, since I really don't know too much about it. In the instruction manual it very specifically states how to correct a boost dropoff problem, and after completing the procedure it has failed to fix the problem.

Besides the Walbro and Profec B I have (that might have to do with the problem):

- Az-tech style Custom CAI
- Racing Beat Turboback Exhaust (air pump removal this weekend).
- Racing Beat F.C.D.
- Autometer Boost Gauge
- HKS B.O.V.
- Street Port (rebuild 4000 miles ago)
- Stock Injectors

I'm not sure what to do at this point. Upgrade injectors? Hybrid Turbo? Help is extremely appreciated.

Thanks!

-Andrew
1990 TII

[edit]Also, note my location. At 1 mile high it is possible to run higher psi safely.

 

bump

 

first of all there is no way you should be running 13psi on a stock turbo, stock injectors, stock IC. you're lucky it's still running.

the boost drop is more or less normal. maybe not that much. but some. the turbo is too small. you definatly need some fuel mods before you can think about a bigger turbo though.

 

I told him. But he said that it was too much drop off. And I also told him to remember the fact that the turbo just can't flow enough at those RPM's specially with a ported engine.

 

Thats not what RETed said. Like I said, I talked to him about this whole thing, including the amount of psi i'm able to run. Remember, as I said before, I live in Denver. Elevation 5250ft+. There is much less air up here, and because of that, it is possible and safe to raise the boost. At least, Ted said with the upgraded fuel pump I would be able to run higher psi. The elevation is not the sole reason.

Anyway. So its the turbo? From what me and Santiago talked about, the exhaust end of the turbo can't handle that amount of air flow, and as it increases, the more the turbo needs to back off. In other words, our stock turbo's can't handle that much exhaust. Or at least more than stock boost. It will drop to 5 psi no matter what on a stock turbo.

So, the solution is a bigger (or better) turbo, with supporting mods.

Correct?

-Andrew
90 TII

 

It's also possible that the spring for the wastegate is weak and is opening up on it's own (unlikely though) Chances are the turbo's just old and on it's last leg. 12psi is about the max you ever want to run on the stock turbo.

 

Alright, I started this thread to get questions answered. It makes sense, so i'll trust you.

Thanks for your help, but as I said before; the solution is a bigger (or better) turbo, with supporting mods, right?

-Andrew
90 TII

 

Yes, a more efficient (larger) turbo won't drop off, and of course you need the supporting mods to do that, or you'll be making 0 boost. Good luck

 

cough cough I said that what a day or two ago? cough cough

 

I always need a second opinion, you know that Santiago. :P

-Andrew
90 TII

 

How much play is there on your turbo's shaft?

Wigle it and move it in and out tell us what you find.

James

 

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try this
http://fc3spro.com/TECH/HOWTO/KWG/kwg.html

 

You need a new/better/bigger turbo and the injectors to support it.

Call BNR. Brian will hook you up.

 

No shaft play. It wouldn't budge.

$100T2> I'm probably going to go with a full turbo upgrade. I figure if i'm going to spend the money to upgrade, it better make a significant difference. So i'll probably go with the TO4S, or a larger ball-bearing. Something that will hold up through 400hp.

-Andrew
90 TII

p.s. Thanks again for all your help, guys.