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

[Mark Strangways]

I think you can put the ecu into test mode where it will fire the outputs to 
some sequence. I am not sure the exact steps, but I am sure it can be done 
even thru the CEL.

Mark
----- Original Message ----- 
From: "Brian Powell" <powellb at gmail.com>
To: <s-car-list at audifans.com>
Sent: Wednesday, December 08, 2004 11:35 PM
Subject: [s-cars] Lost a Cylinder: Who knows Electronics?


> 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
> _______________________________________________
> S-CAR-List mailing list
> S-CAR-List at audifans.com
> http://www.audifans.com/mailman/listinfo/s-car-list
>