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

[thefredx at aol.com]

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...



________________________________________________________________________
AOL now offers free email to everyone.  Find out more about what's free from AOL at AOL.com.