Baffling ... if you get a good nozzle check for both the dye black and pigment black, then it printer should be ok. The nozzle check for PGI-5 pigment black is especially helpful ...wish the other dye cartridges were done like that.
* Hmmm ... but it could be related to ink flow / starvation issues, when you note that:
** Standard / Fast / Bidirectional is flawed, but
** High / Slow / Unidirectional is ok.
* Have you done a print-head alignment? Doesn't seem like that would help, but wouldn't hurt.
* Another possibility, do you have the MediaType set to "Plain"? I think other MediaTypes may result in using the dye inks for black, even when you are using something like WordPad for printing text, or printing emails from a browser.
* Are you using Canon OEM PGI-5 carts? If not, do you have a Canon OEM PGI-5 to try?
* If you refill, it is possible that the cart needs to be purged / flushed to restore adequate ink flow. With enough refills, ink flow can diminish.
* With non-OEM carts from a no-name eBay or Amazon vendor, "all bets or off".
* Another diagnostic if the nozzle check is solid ... print a b/w text page that will really stress ink flow from the PGI-5, using very, very large font. Like 600 pt Arial Black bold, underlined of letters like WM in landscape mode. As big as you can fit on the page.
* But maybe start with smaller letters, definitely with High Quality, as such a test would be very stressful, and possibly harm or even fry the print-head if you really have ink flow / starvation problems.
Other thoughts ... TMI? ... geeky?
* I find it difficult to really see what is going on with a nozzle check on plain, copy paper. If I really need to check closely, I'll use inexpensive, generic inkjet paper, preferably glossy like HP Everyday on rebate special.
* The iP4500 is a really excellent printer, so it is very much worth resolving this issue.
* To me, my iP4500 is excellent for photo printing, but not that much better than any other CLI-8 based printer for b/w text. The relatively large number of nozzles does make for better speed. How much photo vs b/w text do you do?
* For b/w text, my experience is that my old HP 1320 monochrome duplex laser is far superior to any of my inkjets. I find it to be painful to use a slooooooow inkjet for b/w text.
* Here in Colorado at about 6500', my experience is that barometric pressure may be an issue. I seem to get better prints in good weather (high BP) than poor weather (low BP). Perhaps like older cars with carburetors that needed to be rejetted at high altitude? There may be a partial vacuum build up inside the cart when heavy ink flow is happening.
* FWIW, my speculation is that the nozzle check is done in High Quality mode.
