Lizard944

I've been recently noticing some light carbon build up at the base of my spark plugs(all) and on the exhaust tip. Also smells like it's running a little rich. Things I've done recently: Replaced idle stabilizer, temperature sensor, cleaned all grounds, pressure tested for vacuum leaks, checked tps and air flow sensor, cleaned injectors, changed oxygen sensor. My voltage reads at 12.5v either with or without the engine running. Can the carbon be caused by a weak ignition and/or a coil going bad? Can I get away with just replacing the alternator voltage regulator/brushes, or should I go for the rebuild? I have 100k on my 944, with original alternator and coil. Thanks!


Bryon

Lars

The black could be the gas you bought (octane, or different gas station), or it could be bad gas. I had a 931 that would smoke black and make the grass in the back yard turn black. Only on the last 4-10 litres of gas...when I filled it up it went away, then came back on the last ten litres. It's really hard to get rid of if you do have bad gas, for some reason filling the tank up a few times just doesn't do the trick.

Bryan

Try checking the ground between your exhaust system and a good chassis ground, ideally the ground your computer uses. The 3-wire oxygen sensor uses the exhaust system for its ground. If there's a voltage drop between the two grounds, the sensor will get a false lean reading and over-enrich the mixture. There are two temperature sensors on the head, driver's side, toward the front - did you replace both? I believe one tells the computer the temperature, and the other is a switch to tell the computer when to go closed-loop. Either could be the culprit for rich running.

Bryan

Melchior

Before you tear apart your alternator, like I almost did, see if the voltage is being displayed correctly by your voltmeter on the instrument cluster. That was the problem with mine. Remove your instrument cluster and you will find a resistor attached to the back of your voltmeter. This easily slides out of its connections if you wiggle it slowly. The culprit is corrosion in the contacts. Use light sand paper on the resistor and a little in-and-out friction using the resistor in order to clean the contacts in the voltmeter. Don't think that you can go to Radio Shack to find a new resistor: I already tried and they don't carry it. I was a little upset until I found that the resistor was still good and it was just corrosion. Try this, it works! Might as well replace the dash lights while you are in there. I used 5W to replace the 2.5W dash lights that were too dim for my liking. PepBoys calls them European W5W bulbs.

IceShark

David, you might want to check out those 5 watt bulbs. I think they may be melting the plastic back there.

You want to stick with 2.5w or 3.0w. Then do the light tube silverizing job and you will be able to see fine. This is a standard repair that is well documented at 944 Garage or Pelican or maybe even here.

As far as the 12.5v when the engine is running or not, something is goofy here. If Lizard is measuring at the battery he has to be doing Something wrong. There is no way he would keep his battery charged at 12.5v from normal operation if that went on for long - not enough differential voltage. Maybe he is looking at the inside gauge to read the running voltage and your idea is applicable.

In any event, if he has 100k on that alternator I'm damn surprised that there is anything left of the brushes so he should pop 15 bucks and change out the regulator/brushes.