hesitation / bog down

[Andrew Dickinson]

Sounds like a vac leak to me... like Bret said, a BPV is essentially a 
closed loop around the compressor.  leave it open all the time and boost 
bleeds off.  gives a similar problem to AF that leaking vac hoses do.
----- Original Message ----- 
From: "hayes myers" <hayesmyers at gmail.com>
To: "Brett Dikeman" <brett.dikeman at gmail.com>; <quattro at audifans.com>
Sent: Friday, December 11, 2009 2:46 PM
Subject: Re: hesitation / bog down


> Sounds lke i should have a Mityvac. .. I don't think i hae a bypass valve
> but could check. (turns out there was a cut-in on MC2 midstream of 91 
> which
> may make this tricker to figure out.)I did buy a bypass valve (ala Ben
> Swann) but haven't hooked it up yet...could be that it is time. I was
> thinking maybe clogged injectors (had run couple of tanks with injector
> cleaner in the mix)..or perhaps a dying fuel pump.  I'll see if i can't
> follow the checks you indicate below and see what's what.  So begins the
> deeper learning of CIS methinks.
>
> Thanks Brett!
> Hayes
>
> On Fri, Dec 11, 2009 at 2:36 PM, Brett Dikeman 
> <brett.dikeman at gmail.com>wrote:
>
>> On Fri, Dec 11, 2009 at 1:41 PM, hayes myers <hayesmyers at gmail.com> 
>> wrote:
>>
>> >  let off and revs fall off like it's going to die.
>>
>> Classic signs of bypass valve failure, at least on the 20v's; the dead
>> giveaway is when the report is of the engine idle dipping or engine
>> dying coming off a freeway exit ramp.  It's almost always the cause
>> for that exact symptom.  Don't the late 10v MC2s have bypass valves
>> too?
>>
>> If you've got a mityvac, disconnect the control line from the intake
>> manifold and apply vacuum.  The problem can be either the control line
>> cracking, or the valve diaphragm tearing.  It's a $50-ish part, so
>> definitely test before you replace.
>>
>> If the valve is fine (or you don't have one)- maybe check that the
>> metering plate moves smoothly?
>>
>> Oh, also, is the ISV clean and working smoothly?  If it's gummed up,
>> it can stick in a position where it is almost completely closed.
>>
>> Brett
>>
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