Pyzik

I started the car yesterday and this was happening . What's going on ? http://www.youtube.com/watch?v=emkY3uDEwZg

DougM

You need to blip the throttle to trigger the exciter to start the alternator. If you look at your volt gauge, it is too low. The car was idling on 10-11v

Pyzik

When I press the throttle it goes away but when I drive the speedometer and the tech are skipping back from like 60mph to 45mph as its connection is bad or something. And when back to idle it flickers again.

Mrmerlin

First check the battery connections and the ground connection in the hatch
then the 14 pin connector,
Then check the brush holder in the alternator the brushes may be worn enough to fail

Pyzik

Where is the 14 pin connector ?

Pyzik

Ok I'm outside checking things out and cleaned bunch of connections but when I starts the car and and disconnect the negative cable on battery and car dies, is that normal on 928 ?

MainePorsche

NEVER DISCONNECT THE BATTERY ON A RUNNING 928.

Pyzik

How can I check the alternator then?i do have a brand new 200amp from 928ms ready to be put on ...

MainePorsche

Disconnecting the battery while running takes the battery out of the circuit. The voltage regulator, in the alternator, uses the battery to regulate/control voltage output spikes from the alternator. You will damage ECU's controlling engine function amongst other things.
Check alternator output while running by hooking up your voltmeter to the power post on R side of engine compartment and a good ground point (allen key bolt to crossmember is most convenient).

Speedtoys

Why do you need a 200a alternator, you have a 'bad' one..not a weak one.

What was that, $700?

Pyzik

The previews owner gave it to me with the car so I might put in as well.

Pyzik

Ok so I just finished installing the new alternator and not sure how to connect the wires. From the alternator there is two small wires , one for the exciter and one for charging, but there is also side post and the wires I have is the exciter so i know where this goes and then two red cables that are connected together (not sure but on 928 motorsports it shows to connect to the side post, and then I also have a red thick( finger thick) wire that on copper clamp says +, so not sure how to connect them .

Pyzik

Red wires

Pyzik

Ok so I installed it and connected the wires and my flickering problem I gone , but when engine idling it's all good but when I touch the throttle lights get brighter and at post it's 12.30v and when touch throttle it goes to. 14.2 volts , let me know what you think , also drive ability improved and I think my 5k rpm no pull issue is gone ! Also car starts faster unles it's on my head

Carl Fausett

Pyzik,

We have wiring instructions for that alternator on our website if you did not get them with the unit.

Many 928's do not charge at idle - its a long issue that has been chased for years.

That being said, our 200 amp alternator usually does charge at idle when it is wired according to our instructions. As for the voltage being 12.3 at idle and 14.2 at operating rpm range - that is normal, except that the 12.3 at idle is a little low and I think that maybe your battery is down on charge (or bad).

We often hear that the car runs better now - yes - after the voltage is up where it should be the whole ignition system is now back in the range it was designed to operate it and works better. On the fuel side the injectors fire more quickly, the fuel pump can run at the correct RPM now, and fuel pressure is restored. All good.

Drive it for a while to charge it then retest to see what the voltage is at idle. When fully charged and with a good battery, you may see 12.5 to 12.8v at idle.