From: Wally Plumley [wplumley@bellsouth.net]
Sent: Monday, July 30, 2001 2:26 PM
To: 928
Subject: [928] Re: [928OC Public List] sudden death

At 10:28 AM 7/30/01, you wrote:
>Been fighting a problem for a couple of months with no luck.
>
>83S drives fine, but occasionally it will just stop running.  This can
>happen during local driving, idling or highway driving.  No warning lights
>(OXS sensor light comes on after failure  but that is expected).  The engine
>just quits.  Very mysterious.  Mechanic (quite experienced/competent) also
>stumped.  changed fuel filter. checked fuses. pinned out fuel pump, fuel
>injection.  no leads.  probably not that anyway since there is no sputtering
>or other signs of fuel starvation in failure mode.  Probably
>electrical/logic problem but don't know how to isolate.
>
>After it quits, you can start it again anywhere from immediately to a few
>minutes. Sometimes get another failure right away, sometimes not again for a
>few days. As this is my wife's daily driver, this is somewhat disconcerting.
>Any similar probs in the collective memory?


Excellent request for help. You gave the year model, and enough detail to 
start making guesses. Much better than, "Hey - my 928 quits. What's wrong?" 
You even told us who you are!

Some possibilities:

Bad connection at fuse #22 that feeds the fuel pump. (BTW - There are no 
signs of fuel starvation when a fuel-injected car has a fuel problem - it 
just quits. No stumbling, coughing, spluttering, etc.)
Bad fuel pump relay - Relay XVII.
Bad ignition switch
Bad injection relay - Relay XVI

An intermittent problem can be really, really tough to solve, since it is 
good most of the time, and ALWAYS when you are testing it.

The fuel pump relay is triggered by a signal from the ignition system. This 
signal also drives the tachometer, so one quick check is to look at the 
tach instantly when the engine quits. What you want to know is whether the 
tach falls to zero the instant the engine quits, or does it drop to zero as 
the engine quits turning. There IS a difference, but the driver must be 
aware of the difference. If the tach drops instantly, chances are that the 
ignition switch is bad, or there is a bad connection to the ignition 
system, or the ignition system is bad, in that order of probability. If the 
tach holds up after the engine quits running, but while it is still 
turning, the ignition switch and ignition system are probably good, and we 
need to check the fuel pump system.

One approach to the fuel pump system test is to make a test light. Get six 
feet of lamp cord or speaker cord - that is, two-conductor insulated 
stranded flexible wire, of about 18 or 20 gage. Get two small alligator 
clips, and one small 12 volt light bulb.

Cut six inches of the cord off and lay it aside. Solder the light bulb on 
one end of the cord - one conductor to the center of the bulb, one 
conductor to the base. Wrap the base in electrical tape. Attach one 
alligator clip to each conductor on the other end of the cord. You now have 
a six-foot long test light - when you touch one alligator clip to 12 volts 
and one to ground, the bulb should light.

Look at the bottom of the central power panel, and note the plugs. (BTW, 
make certain that all of these are firmly seated!) Plug A is on the left, 
and there is no "I" plug. Count from A to T, then find the red/green wire 
in terminal 5 in plug T. This is the fuel pump power. Split the extra piece 
of 6" wire, and strip 1/4" from each end of one piece. Pull Plug T, and 
stick the stripped end into terminal 5, and reinsert the plug, so that you 
now have a connection to the red/green wire. Attach one alligator to the 
other stripped end, and the other alligator to a good ground, such as the 
grounds above the panel. You may want to wrap the bare wire end and 
alligator in electrical tape to prevent any shorting.

Crank the car. The light should glow, indicating that there is power to the 
fuel pump. Put the bulb where you can see it, and drive the car. If it 
quits, instantly check the bulb - not ten seconds later, but instantly, 
because the bulb should go out as soon as the engine stops turning. If the 
bulb goes out as the engine quits (not when the engine stops turning), you 
have a bad fuse connection or bad fuel pump relay, or the relay is not 
getting a signal from the ignition system.

Let us know what you find.

Wally Plumley
928 Specialists