Steps to fix a bad prelinearization or calibration measuring high DeltaE values

In most cases, the issue lies with the printer rather than the GMG software. A few steps are required to restore proper calibration.

Here's the things you'll need to do

Check if inks are expired - if so you can send out the attached Epson Ink Purge CMYK-OGV.PDF to help purge the ink lines from the bad inks - due to the length of the ink tubes it usually requires running this test file at least 3 times. It also has the added benefit of not adding any additional waste ink to the maintenance box.

If you do decide to run the Ink Purge file please run it using the 'CP_linear' mx4 which can be found in 'C:\Users\Public\GMG\ColorProof\Profiles_Linear' and the full width of the loaded media. If you want to target a specific color you can crop out any of the unwanted channels in the manual job manager.

1 - Run the Nozzle check and make sure all jets are firing. If not clean them till they are OK.

NOTE - If your've cleaned and power cleaned and still have blocked jet nozzles, service is needed.
This could be as simple as a new cleaning blade to a full Pump Assembly replacement. Or a new print head.

2 - Redo the Head Alignments - when they get out of alignment it can change the color.
On the printer in MAINTENANCE you'll find the Head Alignments.
Do the Uni, Bi-D 2color and Bi-D all colors in that order.  This can be done using the automatic method through the front panel.

3 - Agitate all inks in the printer - especially if using the larger 350 - 700ml cartridges.
The ink should be agitated about every 30 days when installed in the printer. Agitate (not shake) for 30 to 45 seconds. And if you like every Monday morning would be fine as well.

And all inks on the shelf should also be agitated about every 45 to 60 days.
For the inks on the shelf agitate them about 15 to 30 seconds.

4 - Do 2 power cleanings to move the ink through the lines. The system is pressurized. If not corrected it can cause color issues as well since the bad ink is still in the line.  If you know which color the calibration is failing, it's only necessary to power clean that print head.

5 - Your print feed advance also might need to be checked. If off it will reduce the color gamut of your printer.

NOTE – The below instructions are for Epson printers only. On HP printers you have an on-board option for Head / Paper feed auto adjustments.

Attached is the PDF 1000mm test file to print with directions on how to use it on the pdf as well. You’ll need to use the PDF with a mm ruler.  Download and follow the instructions in the PDF.

6 - After all this is done run the Calibration again.

Rerun the Calibration - If it still fails select the Details button. Look at the Pre-lin values. If those are the ones that failed look in the DETAILS / Pre-Lin tab. Locate the HIGH DE value – look at original value. That’s the color issue.

Or if the issue is with CMY or K then on the Color tab find the ink values that also have failed due to the high DE values. What ink as at fault? Sort the list by clicking on the DE column to sort it. Click again if the high value is at the bottom.

Look in the Pre-Lin color to see what color it is. Take out the cartridge at fault again and agitate additional time. Clean the Head itself again 2 more times.

If a CMYK value then also find what value the printer was sending - see what  CMYK original values are being used for most of the build. Again take out, agitate and clean twice.

If it still fails you'll need to run a manual job and set the channels to the color of the offending ink.

Create a new Manual Job. You'll find attached a "Ink Fix PDF" file. Use this file.
Make the file the width of the paper - 23 for 24 inch for example. And about 15-30 inches high.
Run the file in the rip. Have it go on hold. Then edit the file like the picture below:

Below is an example if the Violet color was at fault for having a high DeltaE value. 
In channels map all 4 CMYK colors to the PANTONE equivalent and print 1 to 3 times.
This helps move the ink through the lines and get it more stable for calibration and running jobs.

If it's one of the process colors then map all 4 colors to the MX color you have the problem with.
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NOTE - You may need to print this file a couple times to move enough ink through the lines to correct the issue.  Depending on the printer and ink cartridge size, it takes between 6-10% of the ink cartridge to purge a line of ink.

After printing do a new Calibration to see the calibration pass.

7 - Daily and weekly things to do:

Everyday if your going to run a job you should run a nozzle check to make sure they are all firing with no issues. Clean if needed.

If your only printing a couple things a week then every Monday the cartridges should be agitated in the printer.

Ink in the lines will get old as well. So if your not printing very often I suggest get a cheap roll of paper. Run a rich color file again width of the media and about 10 to 25 inches long. And print. This moves that ink through the lines.

8 - Are you using the inline ProofControl for pass and fail on jobs? If so are you seeing the numbers go up after time? That's and indication again of the printer having a changed state. 

9 - Also things that cause the color to change on the printer are Age of the printer, Lot number of the ink, Lot number of the paper, Temp and Humidity.

Temp and Humidity can have a large impact as well. So make sure the area the printer is in has a stable environment. If not this can cause calibration and color issues.