[s-cars] RE: MTM ECU Problem

[Igor Kessel]

Fifield, Douglas wrote:
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> Yeah, that sound familiar.  The repeated stalling, starting, stalling is the
> same thing I experienced.  When I visited with the mechanic last night, he
> started the car and rapped on the ECU with his knuckle, the car died.
> Sounds like the same problem.
>
> I will report back to the list when I know more.

Douglas,
When I chipped my own ECU I decided to do everything right and spare no
expence (hell, I was doing my very own ECU after all), so I ordered from
Mouser Electronics a couple of their most expensive ZIF sockets at
$7.20/ea. The idea was to be able to quickly swap the chips for testing
purposes should there be a need.

So I desoldered the stock chips, soldered in the ZIF sockets, plugged in
a set of EPROMs and fired her up w/o a drama.

After a few mos the car started to give me an intermittent starting
trouble on cold mornings, but there would be no codes stored. It had
progressively gotten worse, to a point that I had to drive with the ECU
lay on the pass side floor, so when the car would start to miss while
driving, I could wiggle the harness or knock on the box and make it run
again.

I had scrutinised both boards a number of times with my engineering
stereo magnifier on my forhead, all to no avail.

Finally I had put together a small breadboard with several red LED's (to
track the power coming in) and one green LED (to track the ground
connection) soldered in to the ECU boards, so that if the car died I
would know exactly which circuit lost its power.

The car died on the road, yet all of the LED's were still lit. Since I
don't believe in miracles, I started looking into the only possible
culprit - the sockets that I have soldered in myself.

Lo and behold, the  512K timing chip in the top board (which is hanging
upside down when the ECU is assembled) had partially worked its way out
of the socket on one side. Suddenly the stupidity of the situation had
dawned on me. I could not believe  that I had been chasing my own tail
with the exhaustive research, while the stupid chip had been dangling
loose in the socket before my very own eyes.

Totally disgusted with myself, I desoldered and trashed both $7.20
sockets and replaced them with the cheap 90-cent regular sockets with 28
positive locking gold plated contacts each. After I plugging in the
chips, I had also zip-tied them to the sockets for a good measure.  I
have not had a single engine stumble since.

A ZIF socket may be a good idea in a home PC, where it sits with its
right side up, and is not subjected to the harsh vibration and
temperature cycles for which the automotive application calls. However,
a ZIF socket makes for a very poor choice in the automotive environment.

Douglas, I am 99% sure that it's either a cold solder joint at one of
the chip sockets or the chip in the top board is falling out of the socket.

--
Igor Kessel
two turbo quattros