Date: Mon, 13 Sep 1999 12:21:52 -0400
Reply-To: John <johnpatt@WARWICK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John <johnpatt@WARWICK.NET>
Subject: Re: Disconcerting Occurances...
Content-Type: text/plain; charset=us-ascii
Roger Bowman wrote:
>
> Hmmm...
>
> Several months ago, an ECU failure (1990 Syncro westie; 175k miles) was
> proceeded by several "drop-outs" where the tach would fall to zero, and all
> engine output would cease.
>
> (description of adrenaline rush and misc. excitement omitted)
>
> Most (except for the final) dropouts could be corrected by jiggling the
> ignition switch, if the dropout did not pass spontaneously.
>
> The final drop-out was followed directly by a tow, and somewhat later by a
> new ECU (which I located for about $400, core included, since my toasted ECU
> was just that; toasted).
>
> Now, despite 18 months, and only about 1500 miles, I am experiencing
> drop-outs (well...only 3-4 so far) again. Yikes! If I had any ECU warranty
> measured in time (instead of injector pulses...) it must be expired. Any
> thoughts as to the source of ECU dropouts (as symptomed by tach falling to
> nothing, and engine output stoping) that comes to mind?
>
> Thanks in advance for your assistance....
>
> Roger Bowman - bowmanrp@ earthlink.net
> Live Smart. Think for Yourself. Transform the Future
Hi Roger,
Thanks for the very informative discourse about coolant, although I only
use Autbahn coolant and reverse-osmosis H2O in my two Syncros.
Regarding your Engine "drop out" symptom, I have some questions. List
diagnosis is very difficult so I'll do my best ..................
Since the drop out symptom existed before and after the replacement of
the Digifant Control Module (DCM), the DCM is not the likely source of
the problem. I question whether the DCM was defective at all. Do you
know for certain that the DCM was as you say "cooked" ? If the DCM was
truly defective it narrows the possible causes. It also indicates that
the replacement DCM is in real danger of the same damage !
Starting with your comment that the tach falls to zero, there is only a
couple a hundred things that could cause this symptom, so a defined
response is impossible at this point.
Your comment about "jiggling" the ignition to restart the engine is
significant since the ignition switch controls the "Run bus" or KL 15
which feeds the DCM (via a power supply relay) and the ignition coil.
The tach is driven from KL 1 of the ignition coil so when the engine
dies, a loss of KL 15 is a likely suspect.
To troubleshoot the run bus (KL 15), WITH THE ENGINE RUNNING, remove the
steering column cover and wiggle the connections to the ignition switch
and the ignition key. Also tap on the power distibution box (fuse box).
Then go the the relay box (L/side engine compartment) and tap the two
relays there. SHUT THE ENGINE OFF and check the connections to the
ignition coil. Look for corrosion, cracks and abnormal electrical
traces.
Then examine the distributor Hall sensor and the external wiring. A Hall
sensor problem can produce the very symptom you discribe.
If none of this produces results, get back to me.
Good luck, JP
