You packed the oil pump with Vaseline? I'm sure this is just something that I have never heard of, but I have never done this other than a bit of assembly lube when rebuilding the pump. I would think that completely packing an oil pump with something as heavy as Vaseline could plug up oil galleries. Once the engine is up to temp, I would think that the Vaseline would thin out and mix with the oil, but if it didn't get warm enough, seems like it could cause an obstruction somewhere. My guess would be the lifters could be clogged with the heavier lubricant.
Or, did I just learn something new when installing a new pump?
I've read about folks saying to do this on the interwebs on engine rebuild sites, but I've never done it...only rebuilt 2 engines though, so i'm not exactly an expert.
Based on what you're hearing when your gauge goes to zero, it sounds like you're actually losing pressure. Does it seem to be related to time or rpm? I know you're breaking in that cam, so you don't exactly want to leave it at idle for too long. But if it takes longer to starve at idle than it does at high RPM, you might have some clogged return passages...or using a high flow oil pump when you don't really need it...or a combo of the both.
Was the block yours before you rebuilt it, or was it from a yard...or someone else? If you know it didn't have a problem before the rebuild, I think that would eliminate a pre-existing blockage in oil return.
If it were me, I'd remove valve covers, take off that distributor and put a drill on it and run it and see what happens. I think the most logical answer is a bad oil pump based on what you've said so far. I think second most likely issue is a clogged oil path(s) somewhere...I know that's vague, but you won't know if it's to/from/both until you run that oil pump by itself with the valve covers off. If you get consistent flow up to the rockers, then you're good at the oil pump to the rockers. If oil pools up and starts draining down the side of your engine, you have a clogged return pathway.
If you get good flow to and from, then there's a chance you got the wrong oil pump. That happened to me when I rebuilt my first SBF. I ordered a Melling oil pump...not the high flow version...and they sent me the high flow version. I just happened to notice a difference in part number when I was about to toss the box before installing.
I know you're getting a lot of fuzzy answers, but at least try the drill on the oil pump shaft, see what happens, and go from there.
I feel your pain...got the whole thing done and it's not working right...90% of the time, it's something stupid...well, at least that's the case when I've touched a project.
Side story: I ran into a couple other issues with my first rebuild...one was nearly catastrophic, and could have cost me my life. It was a 351w that I rebuilt for a 20' aluminum jet boat that I owned when I lived in Alaska. After breaking it in and installing, I took it out on a calm day...cold, but calm...to take it for a cruise. Everything was running beautifully and the torque curve and fuel consumption was way better than I anticipated. I was cruising at 28kts at 2800rpm with a fuel burn rate of 9gph. 4500prm got me to 41kts...way faster than I ever wanted to go in that thing. A little over an hour into my trip, the engine started running a little rough and it sounded like it was eating itself. I was about 20 miles from anywhere, and a good 5 miles or so to the nearest Forest Service cabin. Took off the valve covers, and one of the rocker arms sheared in half. That's what I got for going cheap...used some off-brand rocker arms to save $100. Luckily it was a clean break and nothing got chewed up. Since it was getting close to the beginning of the salmon runs, I had just put my 9.9hp kicker for trolling on the back before the trip, so I was able to make it back home in a few hours. That was the one time I didn't bring any of my survival gear with me (food, blankets, pup tent, fire starter, etc). If it was just me and a paddle, it would have taken me a couple days and at least one night of camping in bear and wolf country. A month later, a Forest Service agent was making a grocery run during one of his trips and broke down near where I did. Unfortunately, when he beached to work on his boat, he landed near a brown bear and her cubs...he didn't survive the encounter. Since then, I've always bought tried and true parts and double-checked part numbers before I install.
Doubtful that you'll ever have a bear encounter due to engine trouble, but it always seems like it's something stupid that causes the issue.
