5ktq electrical issues update...

Bernard Littau bernardl at acumenassociates.com
Wed Oct 1 13:28:20 EDT 2003

Hi Ameer,

What you say is technically correct, the ignition may be close to fully
retarded, but not quite fully retarded.  The odds of that are vanishingly
small, though.  As long as the ECU hears knock, it retards, so unless the
knock goes away due to the retard action, the ECU will always hit maximum
retard, and throw a code and flash the check engine light.

If the knock sensor is damaged or mounted poorly, odds are it will signal
knock independently of the retard.

Your point about the air temp sensor is a good one.  What did you do with
the original air temp sensor for the MAC-11, Cody?  If the wires to the
MAC-11 air temp sensor are open, the ECU will think the resistance is
infinite, which it interprets as very, very, hot intake air -- this will
cause lots of retard.  The signal from the original ECU engine temp sensor
is also still important, to wit:

(From sjm's site:)
In some cases the sensor can be intermittent when the engine warms up, which
will cause some strange rich running conditions because the ECU will
occasionally think the engine temp is much colder than it really is.
Although it is not stated anywhere in the Bentley service information, the
ECU will operate the cold start valve briefly as you begin accelerating when
the engine is cold with a coolant temp below 150F. If the sensor is
intermittent, the ECU may activate this cold start valve when the engine is
warm and this will make the engine run very rough.

Food for thought...

Bernard Littau
Woodinville, WA
'88 5ktq

> -----Original Message-----
> From: Ameer Antar [mailto:antar at comcast.net]
> Sent: Wednesday, October 01, 2003 1:00 PM
> To: Bernard Littau
> Cc: Quattro List
> Subject: RE: 5ktq electrical issues update...
> Maybe the retard is not maximum, but still retarded a good deal, so no
> error shows. It might be worth cheking proper torque of the knock sensor
> bolt. Maybe something wrong w/ the air-temp sensor? I'm just trying to go
> over what would cause an ECU to retard like that. Anyone else think of
> anything that causes timing retard???
> -Ameer
> ---Original Message---
> From: "Bernard Littau" <bernardl at acumenassociates.com>
> Date: 10/1/03 1:44:47 PM
> Subject: RE: 5ktq electrical issues update...
> >
> > Maybe the knock sensor is triggering and retarding the ignition too
> much.
> > If the ECU thinks the engine is knocking and nothing changes that, the
> > will retard the timing all the way, which is not good to run w/ for long
> > periods. This can damage exhaust components b/c the ignition is occuring
> > so late in the cycle. I'm not sure but maybe someone has figured out how
> > to tell when the MAC ECU's are sensing knock, or maybe that was a
> > different ECU. Just a thought...
> >
> This kind of knocking would throw a code and flash the check engine light
> on
> a MAC-11 car.
> Best,
> Bernard Littau
> Woodinville, WA
> '88 5ktq

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