I also read on IRFCA that p4 and 4e are same :-
[2/00] New versions of these with twin-beam headlights, speed recorders and some changes to the control electronics have been rolling out recently [7/00]. WAP-4E are most likely just regular WAP-4 locos from the Vadodara shed. The 'E' suffix is thought to come from the short-lived RDSO directive to denote all air-braked locos and is redundant with the WAP-4 locos (e.g., WAP-1E). There is speculation that some of these locomotives may have some additional features such as an electronic sensor for detecting loss of pressure in brake pipes (hence, sometimes the 'E' suffix is explained as 'electronic', although this seems unlikely). More recently [1/05] many of these have been fitted...
more... with train-parting / pressure loss alarms, and data recorders for speed, energy consumption, etc. All the new ones have roof mounted twin beam headlights, square WAP-5 type windscreens and a digital notch repeater along with a better layout and good seats for the drivers. Some [12/04] even have windshield washers. A few were provided with signalling lamps on the sides but this does not have seem to have continued with the newer units.
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