Fordnatics List Archive

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Mail From: (email redacted)

This read-only message was archived from a public mail list.
Mail From: Paul Nowak <(email redacted)>


My Mustang is the only car that I've ever had that eats batteries. It's
been through 6 in 145K miles ('86 5.0). Last fall I replaced the battery
and the alternator (new, unlimited mileage aleternator) and all was fine
until last Thursday when the alternator baked while driving on the highway
at night. This was the first time the car needed repairs to finish a
trip.

When the car was new I blew two batteries before taking it to the dealer
to find out the starter motor had a short in it. Once replaced it was
better but it still has not been great.

During the past few years, I have noticed that my oil, temp and gas gauges
occasionally all swing to the maxed out position on their dials. This
indicates some sort of electrical problem to me but I have not located the
cause. Also, ever since the alternator blew last week, the car has not
idled well at all -- very unstable idle speed. In '91 when I had a bad
battery, the car would not idle and as soon as the battery was replaced
and the voltage back up, the idle was fine. Now it's acting up again even
though the battery is fairly fresh and the alternator brand new.

I've never been able to sort all these clues out. The car has been a
horse on the mechanical side but the electrical has been something else.

Paul Nowak

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Scott Griffith, Sun Microsystems Lumpyware)

On Feb 21, Paul Nowak wrote:

> During the past few years, I have noticed that my oil, temp and gas gauges
> occasionally all swing to the maxed out position on their dials. This
> indicates some sort of electrical problem to me but I have not located the
> cause.

For your '86, this kind of misbehavior is quite common. The gage
problem is a problem with the IVR (Instrument Voltage Regulator). This
is a very simpleminded thermoeletric interruptor that puts out a
square-wave train that sortakinda averages out to 5 volts. When it
sticks closed, as it sometimes does, it sends all 3 gages (oil
pressure, fuel, water temp) offscale. Its real purpose is to act as a
sort of a degenerate constant-current source and stabilize the gage
movements so that they react only slowly to inputs, so that you don't
see fuel slosh and the like. It certainly does slow them down!

If yours is going west, you can replace it with a new OEM one, or you
can improve upon it. I replaced my IVR with a solid-state regulator
(7805) and have very much liked the results. There's a writeup on this
surgery in "Building the Perfect Pony", which anyone can have a copy
of just for the asking. Drop me private EMail and I'll send you a
copy.

> Also, ever since the alternator blew last week, the car has not
> idled well at all -- very unstable idle speed. In '91 when I had a bad
> battery, the car would not idle and as soon as the battery was replaced
> and the voltage back up, the idle was fine. Now it's acting up again even
> though the battery is fairly fresh and the alternator brand new.

Check out the voltage at idle, then. The EEC-IV can get pretty bitchy
if its supply voltage falls below about 10 volts. You might have
something as simple as a corroded battery terminal or the like- there
are several places that voltage drops can creep into the charging
system. Also rebuilt/remanufactured alternators have been known to
be imperfect right out of the box. If you aren't seeing a good
charging voltage, you might have got a duff alternator.

One other thing to try would be to clear the Keep-Alive memory, and
let the EEC-IV reinitialize itself. If there are no stored diagnostic
codes to go on, you have to start from first principles. But I'd be
inclined to suspect the alternator, even if it is new.

-skod

- --
Scott Griffith, Sun Microsystems Lumpyware
expatriate SCCA New England Region Flagging/Communications worker
(and driver, of anything that turns both right and left,
and can pass tech...) Return Path : (email redacted)
>