My 2003 Windstar has about 150,000 miles on it and is using about a quart of oil every 500 miles. I can't see anything coming out the tailpipe and I don't see any drips on the garage floor. I do see what looks like oil on parts of the engine but if this was the source of the oil loss I thought I would see it dripping in the garage. The van runs fine and doesn't make much noise when running other than some minor spark knock. I've already changed the IMRC bushings which didn't seem to make a difference in oil usage or spark knock.

Any ideas would be appreciated.

Thanks.

I can't see anything coming out the tailpipe
It's very rare to see oil out of the pipe anyway. Usually, it's condensate water that we see out of pipe.

I do see what looks like oil on parts of the engine

That's where the oil is leaking. Throught the lower intake manifold. It's very often on these models. And you will never see oil on your garage when it leaks from here, cause oil accumulates at top of engine.

I guess the oil pressure illuminates on your dashboard?
You don't need to repair the leak.

The knock is under high acceleration?

No, the low oil pressure light doesn't illuminate on my dashboard. Do you think I could be burning off that much oil when I drive the van without smelling it? I haven't smelled it so far and I only see damp spots inside the engine. How difficult is it to fix that type of leak?

The spark knock is typically under hard acceleration. I notice it when mostly when I'm going up a hill near my house where I accelerate from a stop to 55 mph while going up the hill.

Thanks for your help.

Ok, so you burn oil, not leaking it from outside.
1qt/500 miles is reasonable. You'll never smell it if you burn it in that small quantity.
It's hard to repair a leak like that. I don't think is worth to repair a leak like that.

For the knock, it could be caused by a vacuum leak, do you have one?
It could be also clogged injectors or carbon deposit in cylinders.
Try to fill with supreme fuel.

I have the EXACT same problems you describe, except the oil comsumption isn't quite as bad as yours. Maybe 1 quart to 1 and 1/2 quarts per 3000 miles. No drips in garage, no smoke from tailpipe. I'd love to get this solved...

I also had a spark knock that I solved by changing my coil pack. I tried cleaning my plugs and changing my wires but the knock wouldn't stop till I did the coil pack. I could really get it knocking under very light acceleration @ about 45MPH. It's all gone now...

It has a way to test the coil pack. Remove the ignition wires 2 by 2, and measures the resistances between the coil connectors (on same row). You should have between 6.5K to 11.5K ohms. Each row is one coil.

Then disconnect the input coil harness, and check resistance (in coil terminals) between the terminal at front of you and the other terminals. You should have between 0.3 and 1ohm more than the short circuit resistance at each 3 wires. The connectors is at right of the coil.