97 Passport Pinging

I own a 97 Passport and I notice that the low end ower is really bad and the engine pings like creazy under acceleration, when it gets to mid range stops and goes like hell, Now It has new Plugs. I do use 87 octane fuel. Also unless I have my lights on the Volt meter seems to go down under acceleration. Any help would be great.

Thanks

pining can also be caused by carbon build up.

A dirty EGR
Dirty PCV

I would start by trying to clean things up a bit first.

How do you clean up the EGR..
By the way amigo-2k you a re a lot of help, Thanks

Also I order the fuel pump

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7952119697&rd=1&sspagename=STRK%3AMEWN%3AIT

It is supposed to humm from the fuel tank Right??

Because I get no sound at all comming from the tank area.