re. 1.4 bar low boost and recent owner impressions

Ben Swann benswann at
Wed Jan 28 13:28:45 EST 2004


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


[Date: Tue, 27 Jan 2004 21:40:36 -0700
From: auditude at
Subject: 1.4 bar low boost and recent owner impressions
To: 200q20V mailing list <200q20v at>
Message-ID: <4016DAD4.3157.9857A2 at localhost>
Content-Type: text/plain; charset=US-ASCII

Hey 200q20v'ers,

<snip> I took another short trip to see if it's still 1.4 bar 
max.  It is.

Since the boost gets up to 1.4 bar exactly, I'm thinking it's the ECU not assisting the WG 
spring (instead of a leak or bad turbo).  So far I have replaced the WGFV (it was dead), the 
BPV (it was leaking), and the IC hoses (they weren't Samco's).  I've check for fault codes 
(none currently) and ran the output checks (everything's fine).  I've disconnected the MFTS 
and it didn't make a difference.

While I haven't pinched the lower WG hose to see if the turbo can actually make more 
boost, I think I have it down to a couple things.  The throttle potentiometer, or maybe the 
altitude sensor (how common is its failure?).  I swapped the throttle pot with another one that 
I have, without checking either with the meter (I can't find it right now), and it didn't help.


***Noise from bypass mentioned 

Anyway, is there anything I'm missing with the boost issue, and is there anything else I 
should be thinking about with this car?


'91 200q20v, pearl/black comfort, G60's, usually driven daily
'85 4ksq, now an RS2 spec+ 3B project
'86 Coupe GT, now a future MC-1 project
'88 5kcstq, surplus
'88 90, parts
'86 5ktq, parts
'87 5kt, parts]

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