Re: urQ dead on CA 280

[raf40@oes.amdahl.com (Richard Funnell)]

Steve,

This will be a very instructive case, I suspect.  Hopefully we can
collectively think of some preventive maintenance for the rest of us.

>> A couple of monmths back, someone on the Bay area posted about an urQ dying
>> while going South on the 280 (I think it was).  The dealer estimated
>> several thousand dollars to replace most of the electrics.  I'm curious
>> (since I also own that model) to know what the problem turned out to be.
>>
>... that was Gerry Haney.  I helped him to confirm that all of the parts
>that ABPA called bad were.  The coil driver, hall sender on the distributor
>were definiely bad.  In the F/TCU there was a huge Zener that apparently
>shorted out, but He has had the Zener replaced and the unit appears to be
>functional.

I will be interested in the results of that test.  What was the effect of
the zener shorting?  If it is a secondary voltage regulator across the feed
to the ECU (ECU is shorter to type than F/TCU), I would suspect that it
would shut down the ECU, hopefully before damage occured.  I recall that
the car ran with strange symptoms for a few minutes before shutdown.  If
that's the case, I would guess that the zener failure is a result of some
prior failure, perhaps as you suggest.

>He is waiting for me to try out his ECU in my car before he
>buys the distributor and coil driver.  The electronic module that sounds
>the "bell" when you open the door with the keys in the ignition had failed
>also (an electrolytic cap had disgorged itself).
>
>I am convinced that the source of the problem was the battery ground cable.
>I don't know if the thing got corroded or there was some case of excessive
>heating, but the current carrying capacity of the ground cable was severely
>compromised, and my theory is that the battery was no longer an effective
>part of the charging circuit which allowed the alternator to apply excessive
>voltage to the system.

Can you explain this a bit.  I would have thought that a ground cable
connection good enough to start the car that day would be more than
adequate to carry charging current unless it was intermittent.  Even if it
failed, I don't see how that raises the alternator voltage.

It sounds as if possibly the alternator's voltage regulator failed totally
and the alternator tried to pump very high voltage into the system.  Even
with the cable intact, there is likely enough cable (read resistance)
between the fuse panel and the battery to prevent the battery from stopping
the over-voltage condition.  I could easily see this causing strange
symptoms until it fried the zener, which would presumably instantly shut
down the car.

>
>It will be interesting to hear what Gerry believes the problem to be.  BTW
>Gerry, I've been meaning to call you ... when is a good evening for you
>to either drop by or have me come by to pick up your box?  Friday is possible
>or one of the days this weekend would be good.
>
>Steve Buchholz
>s_buchho@kla.com
>San Jose, CA (USA)

Once this is sorted out, I would like to figure out a combination of
preventive checks and permanent indicators to make sure I don't repeat this
experience.  I suspect many others do as well.

So far, a voltmeter in the dash seems like a good bet.  Other ideas?




Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL