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[T3] Won't Start / Injector Puzzlers - Solved (?)

After replacing a couple of sections of my FI wiring harness I have driven the car around a lot, and I feel pretty sure my puzzlers are solved.  I have learned a lot very quickly about our FI.  I'll share a few details of what I learned.

I think the original problem was a bad crimp-on splicing sleeve that connected to the air temp sensor.  I carefully cut open the splice with a hack saw and found a lot of oxidation and only a couple of cruddy-looking wire strands still holding together.  I think this caused intermittent signal loss to the ECU, which caused intermittent missing/stalling/no-start episodes.  The connection looked very solid from the outside.  Every time I measured resistance of the sensor I got a good value for the prevailing temperature.  But I think in every case during "failure mode" I made my measurements at the sensor itself.  In "failure mode" think I should have immediately pulled the ECU and measured the resistance at the corresponding terminal connections as well as at the sensor itself.  

I think my trigger points were OK all along.  I also think my old ECU was good all along.  Recall I swapped it out with a spare I have.  When I made this ECU swap I also swapped trigger points (something I should not have done- bad to change two variables at once).  Anyway, after I did this the problem went from the intermittent stall/no-start to the intermittent dead injectors puzzler.  Injectors 1&4 cut out at or near temp.  I never had the motor intermittently die/no-start with this set-up, probably because I never drove it or idled it long enough for it to happen.  I think my spare ECU (which is a Bosch rebuild) must have a problem that causes one injector pair to just quit at temp.  

I put the old ECU back in, and I found the dead injector puzzler solved, but the intermittent stall/no-start condition was back after a little bit of test driving.  Knowing the sensors themselves were good, and being pretty sure the trigger points themselves were good, I finally went after the wiring harness.  It had been mildly butchered by a PO (crimp-on splices, missing plastic terminal holders), so I eliminated these deficiencies by soldering in some new pieces from a spare harness.  The spare had a few good connectors I needed but is otherwise hacked.  

Two days and about 150 miles later I have not seen any of these old problems resurface.  I got brave and sat in stop/go traffic for about 90 minutes this morning to cross a bridge.  She purred pleasantly the whole time.  

Lesson learned: Don't trust *any* crimp-on connection in the wiring harness, no matter how good it looks from the outside.  Take things apart and properly solder this stuff now, before you get left stuck somewhere inconvenient.  

Other lesson learned: Having a few spares of critical components, like trigger contacts, ECU's, sensors, etc. is nice for diagnostic purposes.  But be careful.  Your spares might be bad.  I think my spare ECU is bad.  When I get time (don't feel like it yet) I'll put the spare ECU back in and see if the 1&4 injectors want to quit again at temp.  

I am cautiously optomistic that everything is back to normal now.  Maybe my wife will stop calling the car "Lucille".  My sincere thanks to all who have helped me through this.  

-Mark Fuhriman
 '69 Fastback 

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