Intermittent no-start MC turbo problem (kinda long)

[veetesse]

Hello all...

I've been having a curious intermittent no-start problem with my MC turbo
swap in my 4ktq and wondered if anyone had any advice.

PATIENT:

The engine is an MC turbo (with Mac-11 ecu) from an 86 5kt and has all the
associated wiring down to the check engine light for code output.  It's got
Ben's QLCC chip / spring package, but no other mods.  Even though this is
installed in a 4kq, I'm hoping the diagnosis would be the same as if we were
talking about a 5kt...

SYMPTOM:

The car will start and run fine with no problems 98% of the time.  I've put
about 7k miles on it since the swap with little to no problems except that
sometimes it will not start when I get in it in the morning (maybe once out
of 75 starts).

This behavior seems to happen only when the car has been sitting overnight,
engine cold and possibly when there's been high humidity / precipitation
(can't prove that last condition though) This only seems to happen if the
car has not been run for longer than 10 hours or so

When the engine fails to start, it'll turn over fine and crank with no
problems but doesn't even try to run.  Upon closer inspection, it appears
that the engine is not getting spark from the coil or to the cylinders.  I
get code 2112 (crank sensors) coming from the ECU when this happens, but I
understand this isn't out of the ordinary since the car is not starting.

Now here's the odd part...  If I do nothing and let the car sit for a few
hours it will magically start as if there's no problem.  It's as if the heat
of the day dries something out, although I can't be sure of that.

I've also got the car to start once or twice after I've moved the car with
the starter (to get it out of the way to use another car).  This is odd
because that means I've been putting huge stress on the starter and cranking
the engine for 20-30 second intervals, then it'll start.

When this engine does start after this intermittent condition, I know
immediately when it'll start because I hear the fuel pump kick on as well as
the buzzing of the freq valve near the air box.

When the no-start condition occurs, I've tried switching coils with a spare,
cleaned the contacts on the coil, inspected the crank sensor connections /
contacts, checked distributor connections, jumpered the fuel pump
(re-pressurizing the fuel system in case it would bleed down overnight),
etc, but nothing seems to help.  Initial distributor timing has not moved at
all.

Any ideas on what to check?  Ignition switch maybe? I didn't have my
voltmeter or the time to check the signal to the coil this weekend when it
happened (twice), but that's on the list for next time... I also haven't
tried switching ECU's since it's pretty well tucked up under the dash/
glovebox area (and covered with plastic to shield from moisture, I might
add).

I hate intermittent problems... if the car was dead in the water, I'd
probably feel better about it since I could troubleshoot with known
variables.  The car is a blast to drive, but find this problem and restore
confidence in the car (daily driver).

Thanks again...

Elliott Bavely
86 4ktq
85 4kq
81 Coupe ITB
83 GTI FSP, 83 GTI 16V
90 VW Cabriolet