Re: alfa-digest V9 #139

[Jon Pike <jhpike@domain.elided>]

> I am using Marelli Plex ignition on a 73 gtv. Since buying the car 5 months
> ago, I have gone through 2 new ignition control modules! The first one
> lasted one week and I put its failure down to a faulty unit, but a second
> unit has just failed. I am fitting it with the heat dispersion contact
> grease as supplied. On both occasions the failure has occurred after I have
> stopped the car - when I go back to start it again it doesn't start. The
> only other electrical peculiarity is that sometimes my headlights are very
> bright for short periods of time (voltage regulator malfunction?) - not sure
> if this may be connected but I thought that I would throw out the
> information. Any suggestions what might have caused the failings of the
> control module would be greatly appreciated. I would love to avoid the
> replacement of unit number 3.
> Thanks in advance,
> Fraser
Hmmm..  Get yourself a voltmeter and observe what your voltage is 
doing..  You might want to attach it semi permanently (thru clip leads 
or cigarrete lighter plug) so it will be sitting there when you have an 
"event".

Proper heat sinking is important, (mounting the part properly and using 
the grease like you're supposed to) since overheating will kill solid 
state electronics.  And when it's under the hood, it's already pretty 
hot to start with.

Having times of unregulated high voltage could blow sensitive 
electronics.. perhaps that ignition module is more prone to blow than 
other things.  Now that I think about it, a 73 probably dosen't have ANY 
other semiconductor electronics except your added electronic ignition!

The intermittent nature of the bright lights sounds like a connection 
problem, whether a loose ground or other connection can cause a "full 
on" alternator situation.. I don't know, but it might be that rather 
than the regulator.  Try wiggling wires on the regulator.  It could be 
internal to the regulator though..

The other thing, if you have a funky regulator, it might not be at a 
proper voltage even when it's not turning your low beams into high 
beams, if that's the case you could be undercharging or overcharging 
your battery.. and overcharging will boil it out over time, and cause 
early failure.  You want to see 13.6 - 13.8 V ideally, when fully 
charged, though in a car system up to 14.4 V might not be too much, 
during charging.  If you see more, you have a problem you need to fix 
fast.. for your battery and other part's sake.

Hope it helps..  BTW, Harbor freight, if you have one near, has very 
cheap meters ($5!) that are good enough for this kind of work..

Jon
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided