1.4 bar low boost MINOR UPDATE

auditude at cox.net auditude at cox.net
Wed Jan 28 15:10:58 EST 2004


I'm trying to combine replies here, and this webmail 
interface is crappy (sorry for the inconsistent or 
nonexistent word wrapping.

> From: "Mike Miller" <mikemilr at blackfoot.net>
> ----- Original Message ----- 
> From: "Dan Cordon" <cord4530 at uidaho.edu>
> I've been following this thread, and if it were me, I'd be 
> doing the same things that have been suggested. Minus one 
> thing.... Diagnosing the low boost condition is tedious, 
> so I'd want to check the actual boost level before diving 
> in to the troubleshooting.

Talk about tedious!  Try doing it with an intermittent stock 
gauge!  =)  My butt-dyno isn't precise enough for that 
resolution. :P  Altho' I really think I'd know if it was giving me 1.8 bar and 217hp.

> Even if you don't make a permanent home for your boost 
> gauge, it may be well worth your time to T in to the feed 
> line for the ECU and measure what pressure is getting 
> there. If it's seeing something in the 10 psi range then 
> you're boost is just fine and it's the display that's at 
> fault. If it's in the 5 psi range, then you know your 
> digital display is okay (even if it's got horrible 
> response time), and it's time to continue with the 
> troubleshooting.

Yes, I have no excuse for not at least T-ing the line for 
the gauge, since I expect to have some form of analog gauge.
I haven't pushed it because I feel like I'm sure that I'm 
getting ECU-unassisted boost levels.  The response time 
isn't a problem, because at freeway speeds when I "test the 
boost", it is rock solid at 1.4 (barely getting there from 
1.3), so there is enough time for the stock gauge to catch 
up I think.  If I had full boost, I probably couldn't 
sustain WOT for this long and get away with it.

> > The few times my car has gone in to *low boost* mode (~1.3-1.4 bar I
> > believe) I can tell instantly. I don't think the 20V is all that fun at
> > 1.4 bar, which makes me wonder....if it really is fun, then you may be
> > getting full boost already.
> Dan,
> If all one has felt is 1.4 bar boost, the 200q can be fun. Just imagine the
> fun it will be when 1.8 is achieved. I purchased my first 200q in May96 and
> it had 1.3-1.4 bar boost. It was much more fun than my 81 4k 5+5. It took a
> couple months to figure out the WGFV was toast ( I was one of the early
> ones - thanks Ned!) - the car was really fun after fixing that!  I recall
> someone saying the difference in 1.3 and 1.8 bar is close to 50 hp.

Well, it's not _that_ fun.  I have about 14psi in my '88 
5kcstq, and it is fun.  The 200q20v doesn't feel like that 
at all, but since the 200q20v is supposed to be so much more 
linear than the off/on boost characteristic of the chipped 
and schrapnelknobben'ed 5kcstq, don't expect it to feel as 
fast.  But I'm 95% sure it's not.  The 80-to-100mph jump 
takes too long, for example.  In the 5kcstq, it's almost 

I guess it's fun because of the torque mostly.  And that 
it's a reasonably fast big comfortable boat.  Speaking of 
which, how about this for a license plate "TRBOBRG" (turbo 
barge)?  Not to make fun of the size of the car.  I wouldn't 
get it, but I thought of the play on word "turbocharge".

I do need to get that boost gauge installed, even if it is 
in the glovebox for now.  I was thinking maybe I could omit 
the center vent and put it in there.  But I really don't 
want to hack any of the nice dash.  I wouldn't mind screwing 
a regular bracket into the A-pillar, but I think if the 
mounting "plate" surface was installed so that the "trim 
bump" is in the notch of the bracket, the gauge would aim up 
at the headliner instead of at me.

Speaking of how fast it is.  I saw a rough-looking 1st gen 
awd DSM car with two or three pillar gauges the other night. 
 I got him to take off, and man that thing ripped like 
nobody's business.  I think his wastegate might be dumped to 
atmosphere (but then again, don't those have integral 
wastegates, so maybe not).  Anyway, my 200q20v wasn't 
keeping up with that.  But it's a great example of what I 
want my 4kstq to be able to spank.

Anyway, here is my update.  I "digitally multimetered" the 
throttle sensor that I had on the car before, and it seems 
to work perfectly on the resistance side of things.  I 
didn't test it as an active circuit tho', with the 5 volt 
reference signal and all.

I'm thinking like the rest of the responses that I got, that 
I need to replace that BPV hose.  So do I need to get a 
cloth braided replacement, or can I just go with regular 
vacuum hose?

Here's one more reply:

"Ben Swann" <benswann at comcast.net> wrote:
> Before reading some of the other replies, I was thinking Bypass valve problem.  Your comment about the noise tells me something is not right.  Also, I recall when I first implemented a bypass operation on my now departed '87 5ktqa(QLCC chipped), I had a mysterious low boost - 1.4 (could maybe top at around 1.6 maybe 1.7 when pushing it hard).  After insisting my install was correct, I ultimately found it was not.  The vacuum control port I was using was not correct.  Some throttle bodies have 2 ports and one produces correct vacuum and the other some partial vacuum.  Anyway I should not have been using any port on the throttle, but a true manifold vacuum source - that resolved the problem and could get the desired boost I needed(over 2 bar0, and I am thankful I did not overspin my turbo, as apparently, bypass was kicking in too soon.
> Don't know how this may help, but have an inkling something may be wrong with what you did when changing the BPV.  
> If not then you likely have some leak that is occuring under pressure, and limiting your boost

Hi Ben,

Well, actually since this car had a BPV already, I just 
unhooked it all at the valve end of things, and never had to 
mess with the other end of the vacuum hose.  After I rule 
out the signal hose to the BPV, I'll verify that connection.

However, that said I would think that the whoosh I hear when 
I shift either wouldn't be there, or wouldn't coincide with 

Why does the comment about the BPV sound make you (and others) think something isn't right?  Isn't it supposed to 
make a noise when I shift?  Granted it shouldn't be loud 
since I have an airbox, and it isn't loud, but the timing of 
the whoosh seems normal to me.

Specifically, my bypass valve has the small vacuum signal 
port facing forward, not up.  This was how it was when I go 
the car, and seems to make sense since the pressure from the 
turbo outlet is acting on the side of the diaphragm.

I bet (and hope) that it is the BPV signal hose.  I can't 
wait to find out! :D

If the question was missed, do I need to use a cloth braided 
hose to replace the BPV signal hose?



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