'87 5KTQ intermittent no fuel, no spark, no-start...

[Ben Swann]

While I am pondering the symptoms you describe, the one thing that needs to be
ruled out is the Coil Assembly, which includes Darlington Transistor.  It is
the only thing other than a wiring issue to the coil that will let you see a
4444 and no spark - I assume you are getting no spark.  I had this happen
recently - car died but would sometimes restart and no faults detected.   If
not getting fuel pump then FP relay is likely not being triggered by the hall
output via ECU - requires signal sync. As below.  Bentley diagram will
clarify.  You may have an intermittent/defective hall sender, but really not
much to go wrong here other than broken wire.  

 

The other thing is to more closely examine the distributor wire and connection
as well as the distributor alignment.  If all three signals - hall,  speed and
ref sensor are not present at exactly the required time, then you will have a
no start condition.  Check that the hall is "In Window"  with respect to cam
and flywheel TDC - ref. procedure in Bentley - in short mark on distributor
must be aligned with the rotor (Hall sensor will be in middle of the window of
the hall wheel) - all this while flywheel mark seen at TDC and cam set
properly.   I recently encountered an intermittent no start condition on a '90
Coupe Q (same setup) and the distributor was such that the mark was just on
the edge of the proper setting.  Turns out the timing belt was off a few
notches and distributor was out of alignment - either due to slippage or
improperly done timing belt.

 

I don't but the demagnetized theory, but I suppose this is remotely possible.

 

HTH!

 

Ben

 

[Date: Mon, 20 Aug 2007 00:53:17 -0400

From: thefredx at aol.com

Subject: '87 5KTQ intermittent no fuel, no spark, no-start...

To: quattro at audifans.com

Message-ID: <8C9B0FD285FD3D7-C5C-9220 at FWM-D45.sysops.aol.com>

Content-Type: text/plain; charset="us-ascii"

 

Hey all,

 I've been mostly lurking here since the early 90's and rarely if ever felt
the need to post a question. As a (former) URQ and current 5KTQ owner, I've
encountered many Quattro brain teasers and usually managed to succeed in
solving the mystery of the year, week or hour. However, my curent problem is a
bit more than I can decipher. My '87(9/86 build) 5KTQ died one night more or
less w/o warning, on the way back from a gig. I finally was able last week, to
dedicate a bloc of time to getting it back on the road.

 

The problem: The fuel pump does not start and the ignition system does not
energize, when the ignition switch is in either the "on" or "start" position.
Input codes say 4444; output codes are all OK. I spent 5 or 6 days chasing
ghosts: fuel pump relay, dirt on speed/ ignition reference sensors, hall
effect, ECU, coil, volt/ohmmeter checks, yada...NADA! But occasionally, it
does start and when it does, it runs beautifully!

 

 

The weird thing is that it only starts when the engine (distributor) comes
(nearly) to rest at the position where the "Hall Effect" window  is open to
the pickup. I realized this after I began "quick clicking" the starter forward
until I could hear the pump start. I noticed that it was at the same location
every time when the pump would start as well as when/if the car would
start/run. (When it does start, it starts instantly!?)

 

My guess is that the reference sensor (or the speed sensor?) is demagnetized
to the extent that it no longer generates a strong enough signal to trigger
the ECU unless it is literally sitting directly over the pin or perhaps when
the pin passes at a very low speed...any thoughts?

Also, how does the ECU know to energize the coil and the fuel pump relay? 

 

BTW. It does have an "Ungo Box" which I have pretty much eliminated as a
cause...

 

thanks,

fred

 

87 5KTQ

formerly:

83 URQ,

83 5kT,

85 5KTQ,

86 5KTQ,

87 5KTQ,

89 5KTQ...]