Here is the WIX 33960. It has a tiny, single stage element inside.
It failed miserably , the instant the test started. Why?
Well, here's the answer.
The center post of the filter head measured
I then (carefully) measured the rubber seal on the filter element, not stretching the rubber any bigger. The "seal" is just a very thin, rubber washer.
The hole in the rubber seal is 0.015" bigger than the post, allowing unfiltered diesel to flow right by.
This is consistent with gently pushing the element onto to post. There is no resistance or feel when the seal and the post meet. It simply goes right over.
This is much different that what you find with the AC Delco filter, which uses a lipped seal to provide a very positive and secure sealing of the centerpost to the outlet of the filter element
And there you have it.... The AC Delco is the clear winner, as demonstrated by filtering, design, and construction.
The CP4's are proven to be far more finiky than their CP3 brothers. Using anything else besides a AC Delco filter is just asking for trouble.
I once contacted the big pump rebuilding houses to get their input on the CP4 failures. They all said the same thing.
1. Considering the number of CP4 pumps on the road, the failure rate is very small and overblown.
2. In every failure they saw, water and not debris was the major contributing factor.
The AC Delco was the best at stopping water.....