She found her spark

It's still February and it's still friggin' cold.  My garage, which has a heat blower in it, isn't warm.  The heater keeps it mid thirties, which is good enough for the cars and melts the snow off of them.  To work on the car, though, I put on an old pair of snow-pants, an old ski-jacket, a pair of boots and a winter hat, and then putter around with work-gloves and tools.  Good times indeed.

In diagnosing what feels like an engine problem on a big old Audi, the internet proves be a scary place.  All sorts of crazy theories about engine breather hoses and pumps, oxygen sensors sending bad data, throttle body sensors messing up transmission control modules; it's frightening out there.  But then there's the "what's the simplest possible explanation?" approach.  The simplest possible explanation was that it was mis-firing, hitting on seven of the eight. 

So in I went.

The very old computer I keep around for the sole purpose of plugging into this car once a year as it’s the only computer I have with a serial port for my cable to connect to the car’s diagnostic port, this very old computer which will boot once out of every three tries and whose password is written in sharpie on its side so I don’t forget it, this very old computer for which I don't have a PS2 mouse but  do have a PS2 keyboard, this very old computer without a working internet card, this one, well, I managed to get her talking to the car and to dump all her fault-codes into a text file and onto a usb stick to print upstairs on the newer computers.  Without a mouse, windows is a prestidigitous combination of alt-tabs, shift-tabs and tab-tabs to fire through menus.  Difficult.

Among the numerous codes warning of low voltage here, bad sensors there, was listed "misfire in cylinder 4."  Ooh, I liked the sound of that.  So off I went swapping out coil packs and plugs from cylinder 4 with cylinder 3 to test but then, lo and behold, the battery died.

I mean died.

I couldn't even jump the car, it was so dead.  Sure, the battery was eight years old, but come on, it had to choose this exact moment in time to give up?  Was the problem the alternator not giving enough juice to spark well?  If there's something sinister broken in the engine, is it worth it to risk $160 for a new battery to find out?  Back to the internet, back to work for a week.  Back to crazy theories.  Could there be bad compression in a cylinder?  How do I do a leak down test anyway?  Do I need to buy a compression testing kit?  Will AutoZone lend me one?

Mrs. Toadroller knows how to cut through the crap.  "Buy the battery.  If the car's gone, it's only $160 bucks.  If the car can be fixed, you'll need it anyway."  I headed off to Auto Zone.  And came back with the battery and a borrowed compression tester. After forty-five minutes I'd wrestled the battery into its snug little compartment, cursing some German engineers along the way.  I fired her up.  The alternator was putting out as it should.  The car was still mis-firing.  Back to diagnostics.  It's only cylinder 4.  Swap out the coils and plugs and it's always cylinder 4.  So my problem was upstream of the coil packs.  Could it be the wiring harness? Internet, what's the deal?

I found a thread on one of the Audi fan forums where someone had the same issue as me.*  Solution: Ignition Control Module (ICM), which seems to act as a modern-day electronic distributor from the engine control module to each cylinder's coil.  $150 from Auto Zone or $42 no-name with positive reviews from Amazon Prime.  Diagnosis requires a digital multi-meter.  The analog Radio Shack ohm-meter I've had for the last 25 years just couldn't handle the range.  Fortunately, Radio Shack was having a going-out-of-business-sale and I got their mac-daddy digital multi-meter for $40.  Sweet.  The thing even has a temperature sender, a decibel meter, and will plug into your USB port with software to operate like an o-scope.  I have no need for an o-scope, and I've never used one (shame on me), so I should learn to do that. 

I pulled the ICM and tested it with the new digital multi-meter.  One of the prongs read open when it should have read 2.5M ohms.  Okay Amazon, send me the new part, let's take the chance.  Two days later a brown truck stopped at the house.  I ripped open the package, took a cold look at the replacement ICM, dressed up for the garage, opened the hood, screwed it down, plugged it in, and had one of the little Toadrollers turn the engine over while I checked for spark by laying the plug against the block while holding it into the spring-loaded coil pack with thick rubber gloves. 

Boy, it’s quite the journey for a V8 to cycle through all of its cylinders twice before you get to the spark on the ignition-stroke.  “Wheedidee, wheediddee, wheedidde, PING!”  Yep, that’s a spark where before there was none.  Thrilled, I put everything else back together, plugged the fuel-pump relay back into place, and opened the garage. After a quick prayer I turned the key, Vroom! I placed her into reverse, scuttled up the ice covered driveway and, with horn-a-honkin’, took her up and down the street for a test ride.

She's back and should be good for another year. 

* I almost never start a new thread anywhere about anything when trying to solve a problem.  Someone has very likely been there, done that before me and documented the fix.  Usually on YouTube.