After cleaning the nozzles, the quality of print is still very poor. What should we do?

Using the printer control panel
1 Load plain Letter-size paper.
2 From the printer control panel, press , and then press .
3 Press the arrow buttons until Clean Cartridges appears, and then press .
A page prints, forcing ink through the print cartridge nozzles to clean them.
4 Print the document again to verify that the print quality has improved.

You may have blocked print head nozzles.
Try the printer maintenance to clear the printer nozzles.
After several deep cleaning attempts and there is no improvements in the print then a new print head is required.

Here's what I found here:

http://www.lexmark.com/publications/pdfs/x5150/eng/ug.pdf

Cleaning the print cartridge nozzles
To improve print quality, you may need to clean the print cartridge nozzles.
Clean the nozzles when:
• Characters are not printing completely.
• White dashes appear in graphics or printed text.
• Print is smudged or too dark.
• Colors on print jobs are faded or they differ from the colors on the
screen.
• Vertical, straight lines are not smooth.
43
You can use the operator panel or the Lexmark X5100 Series Solution
Center to clean the nozzles.
Using the operator panel
1 Load paper in the All-In-One. For help, see page 16.
2 Press Options until Cartridges appears on the display.
3 Press the right arrow until Clean appears on the display.
4 Press Select.
A nozzle page prints forcing ink through the nozzles to clean the
clogged nozzles.
5 Print your document again to verify your print quality has improved.
6 To further improve print quality, try wiping the print cartridge nozzles
and contacts (see page 44), and then print your document again.
7 If print quality has not improved, try cleaning the print cartridge
nozzles up to two more times.
Using the Lexmark X5100 Series Solution Center
1 Load plain paper in the All-In-One. For help, see page 16.
2 Click Start Programs Lexmark X5100 Series Lexmark X5100
Series Solution Center.
3 Click the Maintenance tab.
4 From the Maintenance tab, click Clean to fix horizontal streaks.
5 Click Print.
A nozzle page prints forcing ink through the nozzles to clean the
clogged nozzles.
6 Print your document again to verify your print quality has improved.
44
7 To further improve print quality, try wiping the print cartridge nozzles
and contacts (see page 44), and then print your document again.
8 If print quality has not improved, try cleaning the print cartridge
nozzles up to two more times.
Wiping the print cartridge nozzles and contacts
If the print quality does not improve after cleaning the print cartridge
nozzles, dried ink may be on the nozzles or contacts. To wipe the print
cartridge nozzles and contacts:
1 Remove the print cartridges. For help, see page 38.
2 Dampen a clean, lint-free cloth with water.
3 Hold the cloth against the gold nozzle area for about three seconds.
Gently blot and wipe dry in one direction (this prevents the colors in
the color cartridge from mixing).
4 Hold a clean, damp section of cloth against the contacts for about
three seconds. Gently blot and wipe dry in one direction.
Nozzles
Contacts
45
5 Let the nozzles and contacts dry completely.
6 Reinstall the print cartridges, and then print your document again.
7 If the print quality has not improved, try cleaning the print cartridge
nozzles up to two more times.
8 If print quality is still unsatisfactory, replace your print cartridges. For
help, see page 38.

You'll need a new printhead, QY6-0054-000 around $50.00. www.precisionroller.com has some in stock.

Hi there,
To improve print quality
1 On the operator panel, press Options repeatedly until
Cartridges appears.
2 Press the right arrow button until Align appears, and then press
Select.
An alignment page prints. Once the alignment sheet prints, your
automatic alignment is complete.
You may need to clean the print cartridge nozzles.
Using the operator panel
1 Load paper in the All-In-One.
2 Press Options until Cartridges appears on the display.
3 Press the right arrow until Clean appears on the display.
4 Press Select.
A nozzle page prints forcing ink through the nozzles to clean the
clogged nozzles.
5 Print your document again to verify your print quality has improved.
6 Try wiping the print cartridge nozzles and contacts, and then print your document again.
7 If print quality has not improved, try cleaning the print cartridge
nozzles up to two more times.
Using the Lexmark X5100 Series Solution Center
1 Load plain paper in the All-In-One. 2 Click Start Programs Lexmark X5100 Series Lexmark X5100 Series Solution Center.
3 Click the Maintenance tab.
4 From the Maintenance tab, click Clean to fix horizontal streaks.
5 Click Print.
6 Print your document again to verify your print quality has improved.
7 Try wiping the print cartridge nozzles and contacts, and then print your document again.
8 If print quality has not improved, try cleaning the print cartridge
nozzles up to two more times.
If the print quality does not improve after cleaning the print cartridge
nozzles, dried ink may be on the nozzles or contacts. To wipe the print
cartridge nozzles and contacts:
1 Remove the print cartridges.
2 Dampen a clean, lint-free cloth with water.
3 Hold the cloth against the gold nozzle area for about three seconds.
Gently blot and wipe dry in one direction (this prevents the colors in
the color cartridge from mixing).
4 Remove the old cartridges
5 Let the nozzles and contacts dry completely.
6 Reinstall the print cartridges, and then print your document again.
7 If the print quality has not improved, try cleaning the print
nozzles up to two more times
8 If print quality is still unsatisfactory, replace your print cartridges.

Hope this helps.
Thanks
Have a good day.

The print head is clogged.You can try unclogging manually.WARNING: next steps may lead to a defective of print head, try on your responsibility.
Open the cover and first remove the ink cartridges.Then open the holder and remove the print head.Run hot tap water and put the print head with the nozzles up to stream water.Hold that 5 mins then turn the print head around with the nozzles down.Hold that for every color of 5 mins.Then put the print head in hot water with the nozzles down.Left it water about 15 mins and then you must very nice to dry.When the print head dry put it in printer and start cleaning.If this not help you need to replace the print head.It's part number is QY6-0049.

lean The Print Head Nozzles (Windows) The following contains instructions to check the nozzles for poor print quality and perform cleanings of the print head nozzles as necessary. If print results are faint or streaks are printed, the print head nozzles may be clogged. Print quality can be improved by performing print head cleanings or print head deep cleanings. aution: Only used the approved methods below to clean the print head. Use of other methods may further clog the nozzles on the print head and may cause permanent damage the print head.
Note: It is important to check the cleaning results by printing Nozzle Check Pattern after each cleaning. Cleaning and Deep Cleaning consumes a certain amount of ink. Only perform a cleanings when necessary.
Print a Nozzle Check Pattern

1. Confirm that the printer is connected to the computer and the printer is turned on.
   
   
   
2. Complete or cancel any print jobs in progress.
   
   
   
3. Open the Printers folder.
   
   
4. Click the Maintenance tab. (The Maintenance window opens.)
   
   
   
   
   Note: The layout varies depending on the printer and version of Windows you are using.
   
   
   
5. Insert a piece of letter-sized plain paper in the paper tray.
   
   
6. Verify the desired paper source for the Nozzle Check is selected on the unit by changing the Paper Feed Switch if necessary.
   
   
   
7. Select 'Nozzle Check'.
   
   
   

Cleaning your head might resolve your problem. Perform the below steps to clean the head:

Print Head Cleaning / Head Refreshing If the printed nozzle check pattern is broken, missing, or a specific color is not printed, clean the print head (Cleaning) or print head deep cleaning (Deep Cleaning). Note:

1. Cleaning the print head consumes a small amount of ink. Cleaning too often reduces the amount of ink in the ink tanks.
   
   
2. Print head cleaning is performed when you connect the power cord. Your machine may perform print head cleaning periodically to avoid clogging.
   

Overview:
Step1:
Print the Nozzle Check Pattern.
To check whether the print head nozzles are clogged, print the Nozzle Check Pattern.
If the print quality is poor, perform print head cleaning.
Step 2:
Perform print head cleaning.
This unclogs the print head nozzles
Print the Nozzle Check Pattern again.
To check whether the print head nozzles are clogged, print the Nozzle Check Pattern.
If the print quality is still poor, perform two print head cleanings.
Print the Nozzle Check Pattern again.
Step 3:
Perform deep print head cleaning.
This is a more powerful cleaning.

Displaying the Maintenance screen

1. Ensure that the printer is powered on.
   
   
2. Press the <Menu> button.
   
   
3. Press the left or right cursor to select [Maintenance/settings], then press <OK>.
   
   
4. Press the left or right cursor to select [Maintenance], then press <OK>.
   

Print Nozzle Check Pattern

1. Press the Open button to open the output tray.
   
   
   
   
2. Load letter-sized plain paper in the auto sheet feeder (ASF) or the cassette.
   
   
3. Display the Maintenance screen on the printer.
   
   
4. Press the up or down cursor to select [Nozzle check], then press the <OK>.
   
   
   
   
5. Press the up or down cursor to select [Yes], then press <OK>. (The nozzle check pattern is printed.)
   
   
6. Confirm the nozzle check pattern.
   

< 1 > The normal nozzle check pattern
< 2 > The abnormal nozzle check pattern
< 3 > Some black ink lines are broken.
< 4 > White lines are present in the color ink pattern.
< 5 > Both black and color inks are not present.

Note:

1. When all patterns are printed normally, press the up / down cursor button to select "All A" and press the OK button.
   
   
2. When any patterns are printed abnormally, press the up / down cursor button to select "Also B" and press the OK button.
   

Print Head Cleaning:

1. Display the Maintenance screen on the printer.
   
   
2. Press the up or down cursor to select [Cleaning], then press <OK>.
   
   
   
   
3. Press the up or down cursor to select [Yes], then press <OK> to start print head cleaning.
   
   Note:
   Do not do any other operations until print head cleaning is completed.
   
   
   
4. Print the nozzle check pattern and check the print head status.
   

Deep (Print Head) cleaning:

1. Display the Maintenance screen.
   
   
2. Press the up or down cursor to select [Deep cleaning], then press <OK>.
   
   
   
   
3. Press the up or down cursor to select [Yes], then press <OK> to start print head deep cleaning.
   
   Note:
   Do not do any other operations until print head deep cleaning is completed.
   
   
   
4. Print the nozzle check pattern and check the print head status.
   
   Note:
   If the printed result does not improve even after doing print head deep cleaning, turn off the printer. Then, after 24 hours or later, do print head deep cleaning again. (After a given time interval, ink could dissolve itself, resulting in ink unclogging.)
   

I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
If I've managed to answer your question or solve a problem, please take just a moment to rate this post....thanks!

Hav you replaced with original cartridges or 3rd party/refilled ones? This is a common problem when using generic/refilled cartridges. Let me know that first..

When you say poor quality, do you mean faded printouts, or broken print? Kindly explain in detail, so I can assist you further.

I'm not sure what you mean by lines, but I had poor print quality and even a "ker-chunk" noise in the middle of the print head travel. On these HP printers, there is a strip of plastic with very small stripes printed on it that runs through the back of the print head. This is a linear encoder that lets the printer know the position of the print head. This gets dirty and the optical "eye" can't see the transitions of the lines on the strip. Clean it with some iso-alcohol and water and you should be all set to go.