[urq] intermittent ignition cutout

[Ingo Rautenberg]

Ed,

You could check this fairly easily by plugging the vacuum hose that goes to
the ECU and see what happens with your easily repeatible Cut-out situation
by manually playing with the throttle.  If this changes things (like no more
ignition cut-out), then you may indeed have an ECU problem.

Ingo
----- Original Message ----- 
From: "Ed Kellock" <ekellock at adelphia.net>
To: <urq at audifans.com>
Sent: Saturday, April 09, 2005 5:08 PM
Subject: Re: [urq] intermittent ignition cutout


> What does the "decel valve" do?
>
> It has 3 connections, one goes to the turbo to throttle body hose, another
goes back to
> the bottom of the intake manifold, and the 3rd is a smaller vacuum line
which goes to the
> vacuum tree on the top of the intake manifold.
>
> I ask about its operation because this 3rd smaller hose is the one which
had the worst
> vacuum leak that I fixed a couple of weeks ago when the ignition cutout
seemed to really
> make itself known.
>
> The relevance that I'm wondering about is based on the assumption that the
smaller vacuum
> hose to the decel valve is likely the trigger for its operation and
because the hose was
> split at least half way around at the intake manifold fitting, I figure
the decel valve
> wasn't previously doing much of what it was supposed to do.
>
> It seems fairly obvious that its purpose is to manipulate manifold
pressure before and
> after the throttle plate.  Yes, no, sorta kinda?  Does the decel valve
operate at all like
> a bypass valve?
>
> Earlier today I began to wonder about the closed throttle, open throttle
nature relative
> to my ignition cutout.  In addition to acutating the idle switch, this
activity also
> causes manifold pressure to fluctuate.  I sat down and started rereading
the IST docs and
> began to wonder about the pressure sensor in the ecu.  I was pretty sure
it has the
> ability to affect ignition and I went back thru some old email and found
this from Dennis
> below which states that the pressure sensor can cut ignition when it
thinks there's
> overboost.
>
> It seems I may have discovered a possible tangible link between opening
and closing the
> throttle and the ignition cutout.  I'm thinking it's a big maybe.  Anybody
care to weigh
> in on this?
>
> Ed
>
>
> ----- Original Message ----- 
> From: DGraber460 at aol.com
> To: ekellock at adelphia.net ; urq at audifans.com
> Sent: Wednesday, March 23, 2005 8:28 PM
> Subject: Re: [urq] intermittent ignition cutout
>
> I'm purely shooting from the hip here, but my impression is that the only
true ignition
> cut off these cars have is the over-boost pressure sensor in the ECU, and
oil pressure
> loss? The pressure transducers do go bad once in a while from what I hear.
The load
> reduction relay will not cut ignition- only lights and accessories, and
the fuel pump cut
> off will not make the tach drop to 0.
> I would try to pinch off the tube going to the ECU, eliminating any input
to the pressure
> transducer, and see what happens.
> The flywheel sensors are the only other "usual suspect" in my thoughts. If
the ECU can't
> "see" TDC, it will cut spark. Why that would be heat related is strange
but could happen I
> suppose. The sensors on the head will only make it run rich or lean, but
won't shut it
> down.
> Your car has taken on the early recalcitrant behavior mine showed early
on. Defying logic
> and being somewhat of a bitch.
> Have you swapped distributors with a known good unit yet?
>
> Dennis
> Denver
>
>
> In a message dated 3/22/2005 10:28:09 P.M. Mountain Standard Time,
ekellock at adelphia.net
> writes:
>
> Had hoped that my IC and burnt wire adventures would yield some change to
the cutout.
> Still chasing the wire, so won't know for sure until its resolved.
>
> But, I've gotten a pretty clear fix on the behavior of the cutout, purely
subjectively of
> course.  The cutout does appear to be temperature sensitive to some
degree, though not
> summer heat temp type sensitivity.
>
> The car starts up beautifully and runs nicely as it warms, but as it does,
the cutout
> manifests.  It's almost always momentary and as long as it's not a idle
(even sometimes if
> it is), the cutout is short enough that the engine will catch and continue
running.
>
> I bought some resistors to put in place of a couple of sensors so as to
fake out the ecu
> and either eliminate or isolate the issue.  In looking at the tdc and rpm
sensors, there
> is a 3rd wire for ground.  I haven't quite sorted out how to rig that to
fake out the ecu.
>
> I have swapped in a spare ignition module (thanks Dennis!), however the
behavior was
> unaffected.
>
> The cutout is definitely electrical in nature.  The tach drops to zero and
I think even
> the fuel pump quits, though I'm not positive about that.  I replaced the
ignition switch
> and the fuel pump relay about a year or 2 ago while diagnosing a no-start
situation.
>
> I've been wondering about the load reduction relay.  Mine appears to be
original.  I do
> hear a click when the ignition cuts out.  Haven't been able to isolate it
yet though.
>
> Just a recap and thinking out loud.  I'm open to your thoughts.
>
> Ed
>
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