I have a black line of ink on the back side of the paper when I print anything. It fade through to the front. The line goes down the middle of the paper and is about 1/4 in wide

I do not know for sure but it sounds like the paper is not griped properly, this would cause the jagged lines. I would try another ink cart when the loose paper problem is resolved. I hope this helps.

This is usually a piece of paper stuck in the machine after a paper has gotten jammed. look carefully around the area where the printing is done and near the exit slot.

Got to Printers and Faxes in Start, Right click on the icon for the printer, click properties, click maintenance and try cleaning the backing plate from there.

black developer rollers need replacing.common fault.

if you do your own refill the ink u are using is of the wrong density, get the right ink

It might be a dirty led assembly. The leds hang down from the top when it is opened.

the waste ink pads are full ..when the black line appears it is an indicator that the waste ink pads are full it is usualy because the printer has reached its life expectancy the solution is either buy a new printer or pay a tech about 170 dollars to repair it

I have exactly the same problem with a Canon Pixma MP800, I have cleaned the rollers, changed the ink cartridges and reset the printer. It will print a few pages cleanly then dump black ink on the roller which leaves a heavy black line on the back of the page. It fades away after printing about 10 pages and then a few pages later appears again. The printer is two years old and it looks as if I must buy another. Should I buy another Canon?

Is the line on the front of the page or on the back? If on the back, you need to clean the platten which is the piece of plastic under the paper.

If its on the front, and you say "It lools like a rubber cover may be missing off of one of the rollers", could you upload a picture of this roller? I don't recall any covers on rollers in Canon printers.

Try this, print out a blank page. If line is still there, print out 10 blank pages. If line is still there and has not faded, this is unusual and may need servicing. There may be a problem with the encoder strip (it's a clear plastic strip with black lines running the length of the printer slightly behind the head), Try cleaning it on both sides with a little windex on a q-tip. It's delicate so be careful.

If the line looks faded after printing 10 blank pages, some ink has dripped onto something that is contacting the paper. This could be a roller, the bottom of the head carriage or even a hair or piece if dust that is stuck in the machine or on the bottom of the head. In this case, I would recommend cleaning everything. Revove the head (tell the machine you're going to replace ink, and when it moves the head into the centre position unplug the power cord.

Remove the head and clean off any dust or hairs on the bottom. Run a Q-Tip along the bottom of the carriage assembly wherever you can. Clean any accessable rollers. If you can get at it, clean the wiper on the purge unit (the unit the head sits over when it is parked), as well as the seals.

Reinstall the head and ink, close the lid, power up and retry printing.

I hope this helps. If not, there could actually be a fault with the printhead or one of the circuit boards

I have same problem, with new ink cartridge, also tried cleaning the print head, no luck.