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The first question to be asked is is it truly actual E Coat?

True Electrostatic Coating is a rust inhibiting coating and it sticks to bare metal extremely well. It is what you are trying to mimic when you spray your bare metal surfaces with epoxy primers.

The test is to use a urethane grade reducer and wipe a spot. True E Coat will not soften and end up on your rag. If it does, it should be removed and the panel should be epoxied.

 

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As far as whether or not to sand/scuff the E Coat prior to applying your 2K urethane primer, that depends on the primer manufacturer's recommendations.

Most will recommend scuffing but Spies Hecker will tell you "absolutely not", because any sanding or scuffing of the E Coat compromises the coating and destroys the rust inhibiting aspects of the coating.

They require just a good cleaning with wax and silicone remover (Pre-Clean Solvent), then apply the primer directly over it. It took me some convincing when I started using Spies products, but sure enough, it sticks like glue, never peels, even when taped on after painting to do two tones or graphics, and we've never had a comeback from adhesion issues.

Most other paint manufactures will suggest scuffing the E Coat, even though it compromises the integrity of the coating, because their primers will not adhere completely without the abraded surface.

Another note is, no paint manufacturer will recommend sanding E Coat and painting directly over it without priming first. E Coat is simply a shipping primer, that sticks extremely well to bare metal and inhibits rust,...paints do not stick to it, no matter how it's sanded or prepared.