The fellow at Autozone tells me that an alternator should be putting out 14.4 volts in order to recharge battery and power the car. The alternator charge gauge on my Porsche 944 reads a hair over 13 volts but then it has little to run. Is 14.4 correct?

 

yes, 14.5V is the "normal" voltage output but it is always specified at a given engine rpm's.
At idle voltage will be less. Run your car to 3000 rpm's and check voltage ( with a voltmeter, not your car gauge)
Anything less than 14v mean that you have a problem, alternator or voltage regulator

 

Yes, it is or at least something over 14v.

 

Well, I got battery charged but now the thing just won't fire at all. It was firing but not keeping lit after the first cylinder fired. I've put two bottles of fuel injector cleaner in in the past month because we were driving a lot and I was filling the tank.

 

Just to be sure, are we trying to start a Porsche 944 or a Jaguar XJ8?

You do not mention any CEL codes so . . .

First thing I would suggest is to measure the battery voltage while cranking the engine. If we are working on a Jaguar the starter is capable of spinning the engine at a voltage level below the point that the electronics will function.

If the engine is spinning and the voltage remains above 10.1v, hopefully well above 10.1v, check the fuel pressure at the Schrader valve at the rear of the right valve cover. Should be above 40 psi or by squirt test spray gas when ignition is turned on to position II (on but not engaging starter). Hold any lighted tobacco products in the hand furthest from the spraying fuel.

If no pressure check the pump fuse and then swap the fuel pump relay with another. If still no pressure probably pump problem.

If pressure, swap the ECM relay with another.

Still nothing, come back and we will try again.

 

Underneath the butterfly, the throttlebody is fuzzy with buildup. Think that might have something to do with my problem? Is there a good way to get it out without having it fall into the intake system?

 

Here is a link to how to clean the throttle body: Jaguar throttle body cleaning xk8

. . . but I really do not think a cruddy TB alone is going to prevent the car from starting.

Once we got past a battery problem you seem to be describing a fuel pressure issue. I would ensure that the car was generating 40+ psi of fuel pressure at the Schrader valve on the fuel rail.

 

I took the battery back to Autozone after three starting attempts and the tester read that it had 40% of its charge remaining. After having it re-charged again, the tester said that it had normal wear. It is a four-year old aftermarket battery made in late 2007 which means it probably has about four years use. I reinstalled it and tried to crank the Jag. It still seemed to be dragging. My 30 someodd-year old Radio Shack multi tester told me earlier today that the voltage while cranking had dropped to 11 volts. I'm afraid that this thing has multiple problems and that replacing the battery is only one of them. Is the Shrader valve that thing that looks like an inverted mushroom behind the right head and has a tube which connects with others and has a short, rubber covered tube extending from that?

 

The Schrader valve is nothing more than a tire valve, at least inside. Depress the valve pin and gas will spray out. Check with an auto parts store to see if one of your local ones will 'rent' one. Otherwise Harbor Freight for about $20.