[s-cars] Lost a Cylinder: Who knows Electronics?

[Brian Powell]

Greetings, driving home last night, I suddenly lost power and the
engine ran very rough.

Got home, pulled injectors and found it was cylinder #5. Swapped
POS's, still #5. Swapped plugs, still #5. Swapped injectors, still #5.
Tested the coil with a gap tester, and when you would turn on the
ignition (not even turn to start), it would spark, then, turn to start
engine, and #5 would not spark again. Bad coil, I think to myself. I
replace that coil with a spare I had. Same symptoms.

Okay, turn to Bentley page 28-09 and test the ECU to POS leads with an
LED tester. Cylinders 1, 2, 3, and 4 all check out. Go to pin #3 on
the second 4-pin POS connector (corresponding to cylinder 5). The LED
lights up when you just turn on ignition (engine off). When you turn
over the engine, the LED doesn't blink for each firing signal like
every other cylinder. Check for short between ECU harness and POS
connector: checks out. M***er F*****!!!!

ECU seems to have a short on cylinder 5. UGHHH!

Take apart ECU. Start tracing back from pin 21 to see what I can find.
All of the cylinder Pins feed to a bank of 5 resistors which then
connect to some custom Seimens chip. Okay, let me test the resistors.
They are BROWN-BLACK-BLACK-BROWN-BROWN which corresponds to 1kOhm with
1% tolerance. I test each resistor and every cylinder comes in at 997
Ohms EXCEPT the resistor for cylinder 5.

Cylinder 5 measures 977 Ohms when I measure it in one direction and
999 Ohms when I measure in the other direction (i.e. common on left
side then common on right side). This makes no sense as the resistor
shouldn't care. All of the other resistors measure precisely 997 no
matter how I measure them (I have checked this 15 times now).

My question is thus: This resistor is outside the specs on the
resistor sheet for the given color code. Those who are electronically
inclined, could it being roughly 3% out of spec (for some reason in
one direction) cause this short that I am getting? Essentially coil 5
is always on except when cranking the engine. If so, I can simply
unsolder this resistor and solder in another 1kOhm resistor.

I can't afford another ECU right now unless someone wants to sell me a
busted ECU cheap and I can try to make one good one out of two.

Any help and suggestions are greatly appreciated.

-- 
Cheers,
Brian