The oil pressure gauge in my van has been dropping down to 0 and then going back up again for the last month and a half or so and since I couldn't afford to have the van worked on, I just hoped it was just a screwy gauge.
Yesterday the engine started knocking, so I'm assuming that the oil pump really is dead and I'm risking the engine if I keep driving it this way.
I can get a used pump for free, but I don't know where the oil pump is located or how difficult it is to swap out. I've been told that it MAY be in the oil pan itself but it may not, but that's all the info I've been given.
I'd greatly appreciate any help you can give with this. This is our only vehicle and funds are extremely limited so do-it-yourself is pretty much the only way to go.
Thanks in advance & happy holidays.
 In case it's related, I should add that I've got kind of a strange intermitent acceleration problem; every so often, I lose acceleration, almost as if I've taken my foot off the gas, but then things return to normal. There doesn't seem to be any rhyme or reason for this; it happens when I'm taking off from a stop and when I'm driving along at speed. It happens when I'm driving slowly around town and when I'm doing 100km/hr on the highway.
I wouldn't think oil pressure would effect acceleration like this, but my knowledge with this kind of thing is pretty limited.
OK Christmas and all, most advisors have not really paid to much attention to the web site.
Your oil pump is located inside the oil pan. As you have descibed the issues and situation here, I do not think that you have the tools and expertise to do this. The motor mounts need to be taken off and the engine lifted, a lot of the top parts have to come off to get extra clearance. Reinstallation is a little tricky to prevent oil leaks.
Lets start here.
What color is your oil: clean like a fresh fill, Black as midnight or a little milky?
Next I need to know about your last tune up.
When was it and what did you have done. (Plugs, cap & rotor, PCV valve, air filter, fuel filter)?
When did you last change the spark plug wires, and if you are inspecting them now are the seated properly on the plugs and the cap. Are they touching anything? Do they have a white burn mark anywhere on them?
Check those items and let us know.