mine was doing it also on a 4.2lt diesel Nissan patrol, I just swapped it over to a 4601 today and I will see if its different after the thread sealant sets. I haven't got a dedicated relay or special power source though which I think it need but the 4600 survived for 2 years in harsh conditions in rugged far north QLD Australia under a 4wd so no complaints about its performance. I only got 3psi after my filter on the engine side on idle so I upgraded today as I said to get more flow when I am pushing it.
Absolutely, I did change from the original Carter 4600 to a higher pressure 4601 about a year ago as I wanted higher pressures at higher revs. The original 4600 is now a spare, not that it gave me any trouble over the many years of service and I'm not expecting any from the 'newer' one either. Be aware they are noisy when you stand outside, but once you are inside and driving you don't hear them.
After much thought I consciously fitted the pump with no pre filter, they are a tough pump. You will need to mount it on the rubber mounts they supply.
