latest on boost saga

Wed Dec 17 19:21:30 PST 2008

Hi Robby,

I'll take a stab at it here as I have BTDT with low boost when I bought my 1st 200q in 1996. I had a normal reading on the WGFV but it was bad - Ned Ritchie of IA and I spent many hours troubleshooting it and I think mine was the 3rd one found to be bad in the US. Took over a month to get the part from the father land.

If you pinch of that hose from the WGFV to the WG, you will remove ALL ECU control of the WG. Have you done that yet? 

You say you have a new Bypass valve correctly installed. Have you verified the hose the entire length from the back of the Intake Manifold to the Bypass valve? If anything is bad ( like it is crimped at the bracket on the back of the IM) the Bypass valve will dump boost prematurely.

Good to hear you have the Samco's - that should eliminate any leaks there - which would show up on a pressure test anyways. 

I don't recall what you are seeing for low boost when you do experience it. Is it possible the car is in limp home mode ( 1.3-1.4 bar) due to a bad MAF sensor? Try to borrow one if possible as they are quite expensive.

There is a high altitude sensor - when I turn on my key at 5000 ft elev. the boost gauge reads .9 or .8 bar. With stock ECU I would never see over 1.7 bar and yet I would get 1.8 bar under about 3000 ft elev. At 10k+ ft elev boost was limited to 1.6 bar as I recall. The purpose here is to prevent over spinning the turbo in the thinner high alt. air. I guess they figured 100k rpm was enough :-)

Basically, the WGFV is the way the ECU controls boost - it pulses the WG and prevents it opening at lower boost and then it allows it to open as you approach the max boost your ECU allows. If you exceed max boost ( like with the hose pinched off or a stiffer WG spring) the ECU will ground the fuel pump and not allow you to exceed 1.3-1.4 bar until the ignition is cycled.  

Your problem (to me) sounds like an issue with either the hose to the bypass valve or a flaky MAF sensor. If you are running a K&N air filter, some people have experienced the oil from the filter coating and ruining the MAF sensor - I have never had the problem personally. I am assuming you have checked the air filter - I did have a rodent build a nest in my F350 airbox a few yrs ago the severly limited boost. Little SOB chewed out the bottom of the filter and used it and sone underhood insulation for nesting material. Went from 24 lbs boost to 14 lbs.

You may not know that you can driil out the top of the WG in the center and tighten down the screw inside to increase spring pressure - allows for faster spool up of the turbo - same as putting in a stiffer WG spring only "free".

I think I saw where you said you had checked *every* fuse in the fuse box. I think there are a couple there that will limit boost - like that double one nearest the fender in the middle with "moteur" or something like that labeled on it.

Just out of curiosity, what are you seeing for fuel economy? I'm running an MTM chip ( have run stock and Hoppen stage 1) and I see 21-22 around town and 25-28 hwy. The reason I ask is that a clogged Cat-con can cause low mileage and low boost. A loose part in the exhaust will occasionally allow normal performance. Just one more thing to look at :-)

hope some of that is useful

mike

----- Original Message ----- 
From: robert weinberg 
To: 200q20v at audifans.com 
Sent: Wednesday, December 17, 2008 5:53 PM
Subject: Re: latest on boost saga

hi mike,

it's an 034 billet bypass. it was installed correctly.

i wish i knew what the stock ecu did but i bought the car with a dead autocheck. boost, trip, etc. i chipped the car while it was still dead.

i developed the boost issues. somewhere in between, i got around to frankensteining a another dash's electronics (that white flip down back panel) onto my dash which fixed the autcheck, et al.

i'm also running samco hoses - any leaky boost and vaccuum lines were just replaced by 034.

there's definitely something screwy going on with the computer and the wgfv. it's reading 1.4 bar like it's not even connected - but it is. 034 tried a known working valve. no change. they measured the correct signal from the computer to the connector.

but something is getting mixed up. and sometimes, it works and the car is a flippen rocket.

help me learn, what is the purpose of the whole WGFV system? to allow the computer to lower boost at high altitude?

from my understanding, that's the only time the computer lowers boost. it does not lower boost during detonation, correct? only pulls out timing.

Regards,
Robby

--- On Wed, 12/17/08, Mike Miller <mikemilr at blackfoot.net> wrote:
From: Mike Miller <mikemilr at blackfoot.net>
Subject: Re: latest on boost saga
To: 200q20v at audifans.com
Date: Wednesday, December 17, 2008, 4:39 PM

I forget - has the turbo bypass valve been replaced and is it hooked up
correctly? It is easy to hook up backwards which I believe can limit boost. What
kind of boost does a stock ECU make when installed?

mike

----- Original Message ----- 
From: Chris Miller 
To: 200q20v at audifans.com 
Sent: Wednesday, December 17, 2008 5:15 PM
Subject: Re: latest on boost saga

I'd hook up a test light (LED) to the wastegate frequency valve (WGFV).
That way you can watch what the computer is telling the WGFV to do.  If I
recall correctly, the LED should light up solid then flash rapidly as boost
builds.  If the light stops flashing or goes off, that means the signal from
the computer is not closing the WGFV and you'll have the 1.4 bar boost max.
Make the lead to the LED long enough and you can stick the LED under the
windshield wiper and watch it while driving (or run it in the window to the
dash).

Check the basics, too; grounds; wiring condition at the multifunction temp
sensor; condition of the gear on the end of the distributor.

Chris

On Wed, Dec 17, 2008 at 10:42 AM, robert weinberg
<centaurus3200 at yahoo.com>
wrote:

034 says they GAURANTEE they've checked every flippen sensor or possibility
with the car. at least she did boost for a little bit with my computer. Dan
at 034 said he can believe the ecu going bad - like the pressure transducer
- but what would make for a flakey chip? they are open to suggestions.

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