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Re: UrQ FTCU ground on the intake - LONG


Scott said:
> >and HV ignition noise coupling into dist. hall sender
> >signal......that last one was a bitch to figure out....

Paul asked:
> Whoa, you lost me on that hairpin left over blind crest,
come again?

You rally guys, always using those interesting

As I mentioned this particular ur-Q  had several problems
that were making the car cut out, sometimes a fuel pump
cutout, sometimes an ignition system cutout,  sometimes
while cruising along, sometimes while under heavy
acceleration/high boost. Sometimes, sometimes,
sometimes..... The darn  cutout problem(s) was very
intermittent and it was very tough to get it to fail WHILE
you were driving it. 

I had several kinds of DMM's, oscilloscopes etc connected
up to the thing to monitor ECU, Ignition coil, Ignition
Control Unit signals while I was driving along and finally
fixed the 3  problems previously mentioned.

Once I sorted out the problems with the fuse box, air temp
sensor and modified the ECU to raise the over-boost fuel
pump cutout, the darn car would STILL occasionally lose the
ignition drive signal (ECU pin 17) from the ECU to the
Ignition Control Unit (ICU Pin 6) mounted above the glove
box area. This occurred ONLY under heavy acceleration and
high boost. The ignition would shut off while under boost
and heavy acceleration, but would immediately restart as
you coasted to a stop. 

For awhile I thought the return ground wire from the ECU
(Pin 2) to the ICU (Pin 3) was intermittent but eliminated
this as a cause. The later ur-Q ECU's have a mod done at
the Hitachi ECU factory to the internal circuit board to
ground this Pin 2 inside the ECU instead of getting this
return ground from the ICU ground. Basically there is a
transistor inside the ECU that is driving a darlington
transistor pair inside the ICU and the ECU transistor
emitter ground return was being supplied from the ICU.
Yada, yada, yada.........

Well, I checked out every signal coming into and going out
of the ECU using a portable oscilloscope (not a trivial
task while driving the car) and they all looked fine except
for the distributor hall sender signal coming into pin 22
on the ECU. This signal looked fine under normal driving
but when you stomped on the throttle there was a lot of
noise spikes showing up on the signal which were almost at
the same amplitude as the main signal.

I found that this was caused by the HP aftermarket spark
plug wires that had been installed and the fact that
several of the these ignition wires were laying directly
across the hall sender wires coming out of the distributor.
I relocated the spark plug wires and the noise was gone, so
was the intermittent cutout. I surmised that the ECU was
"thinking" the hall sender signal was gone or it got
confused when it saw "extra" timing signals and just shut
down the ignition drive. Sometimes a "visual" inspection
can help solve all kinds of problems....before dragging out
the expensive test equipment.....

Here's hoping your trouble-shooting adventures never get so

Scott Mo.