[Diy_efi] CS Failure

Tue Nov 29 02:47:17 UTC 2005

Tom,

I have a 1998 BMW 540 that eats one or two rear taillights each month.  I've
never seen anything like it in over 20 years of car ownership and 19 cars.
The battery is in the trunk, I assume all power goes forward to the engine
before coming back to the taillight assemblies.

I did put my oscilloscope on the car once to see if there were any weird
spikes, didn't see anything.

I've cleaned all the bulb sockets, cleaned the multipin connectors, even
tried conducting grease at the contact points.  Still loose one or two bulbs
each month.  Any ideas here?

I'd drive it into your shop and pay for a proper diagnosis if you're
anywhere close to western Pennsylvania!

Thanks,

Dan Nicoson

  -----Original Message-----
  From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of Tom Visel
  Sent: Monday, November 28, 2005 12:38 PM
  To: diy_efi at diy-efi.org
  Subject: Re: [Diy_efi] CS Failure

  I own a repair shop specializing in electrical and driveability diagnosis
and repair.  If my shop had no overhead, I could probably retire on the
income I make from alternators which other shops (or customers) installed
and had die on them due to high resistance in the output circuit.
Intermittent or poor lamp circuit (L terminal) connections will cause
intermittent no-charge problems.  Poor or no connection at the sense (S
terminal, the big one in the regulator connector) may cause the alternator
to undercharge, but rarely to overcharge or burn out.  What burns out
CS-series (and indeed, all) alternators is heat.  Internal heat, cause by
overwork because the alt can't charge the battery properly and/or can't
monitor the battery's state of charge.  To diagnose your vehicle:

  With a fresh known good alternator and a fully charged battery (12.66 V or
better) installed, check the voltage drop on the positive and negative sides
of the charging circuit.  To do this, get the alternator under a good load:
engine running, lights on, heater blower and A/C running, cooling fans going
if you have them.  If you have an ammeter, clamp type or no, measure the
current flow through the system.  Positive or negative side will be the
same, and be sure to include all of the wires at the battery in your
measurement if using a clamp-type probe.  Note the reading.

  While the engine is still running, using your DVOM, measure the voltage
between the alternator case (the case thru-screws are good candidates) and
the battery negative terminals.  Note the reading.  Now measure the voltage
between the battery positive terminal and the alternator output stud.  Note
the reading.  If you got negative readings, ignore the sign.  It's the
number that counts.

  Total your two voltage readings.  This is the "voltage drop" in the
charging circuit.  It is a reflection of the resistance in the circuit -
resistance which will put a long-term strain on your alternator's diodes and
overheat and kill them.  If you get a total of greater than 0.1 Volt per 10
Amps of alternator output, that is too much voltage drop and the connections
and/or wires and cables will need to be improved.  For a standard 105 amp
CS130, 10 gauge wire straight to the battery, with a 14 gauge fusible link,
is sufficient.  For a "high output" alternator, 8 gauge with a 12 gauge
fusible link is recommended.  Also, you can't have too many grounds.
Besides keeping your alternator alive, quality grounds (less than .050 volts
drop) will help stave off computer stupidity.  You would be astonished at
the number of vehicles that leave my shop with a sub-$150 repair (diagnosis,
labor, parts, tax) when other shops told the customer that s/he needed a new
ECM or a stack of new sensors.

  TomV

  Clayton Martiniuk wrote:
    Hello, I have an 1994 Chevy 350 that Keeps eating alternators for some
reason. They seem to work for about two days and then shit out. I have a cs
series alternator powered with one exciter/indicator wire at the F terminal.
Looking at the indicator bulb, I'll start the truck, the light will go off
for a while but turn back on intermittently. I heard that these years of
trucks seem to have a problem. Some say to ground the back of the case to
the batt but I dont see how on mine. I am probably close to duty cycle but
no major power drains. It gets very cold here around -20 to -50. I am
running an electric fuel pump. I am running an red top optima with 800 cca.
Does this Battery require special needs? Is the answer an larger amperage
generator or am I doing something wrong?
    I am sick of buying alternators and no one can seem to figure out whats
happening.
                                                    Thank you for your time
                                    Clayton Martiniuk
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