No Oil Pressure After Rebuild? Help!

So me and my dad recently rebuild the 4.6 DOHC out of a Mach 1. Putting new everything including a Ford Performace high flow oil pump. We primed the system with the big sprayer pump method. Pumped almost 5 quarts and then topped it off thru the valve covers. Upon start up there was virtually no oil pressure for a good 5 seconds so we quickly shut it off and suspected a bad oil sending unit. As we were putting a new one on we realized that before the rebuild the oil pressure showed fine on the gauge so why would the unit go bad within the time of the rebuild, so instead went out to get a manual gauge and hooked it up to where the electric unit screws into. The needle did not budge. Getting desperate we finally undid unit and left the hole open and cranked the engine over with a non programmed key so it would just crank and not fire up, just seeing any signs the oil pump was working and hoping oil would squirt out of the hole. Not even a drop came out. At this point I don't know what to do or suspect. I'm guessing the oil pump if defective but it just seems like a really slim chance a brand new ford pump would not work like that. The pickup tube also had clearance as the oil pan went on smoothly without any force having to be applied. Getting ready to pull the **** front cover off and see if I can see anything that went wrong with the pump. Has anyone ever experienced this? I would love an answer or insite of what could be the source of my problem, if not the pump. Thanks guys

wmburns said:

Which model oil pump was used? When installed did the oil pump discharge port line up with the oil port in the block? Did you use an O-ring in the oil pick up tube? A vacuum leak on the suction side of the oil pump would destroy the prime.

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MPN# M-6600-D46. I bought it off American Muscle. Yes, the pump only goes on one way with the shafts of the crankshaft and both ports matched up. The kit also came with a new pickup tube with O-rings supplied, so those were also used.

wmburns said:

On final thought is to remove the oil filter adapter and confirm that there isn't anything blocking the discharge port on the block.

Barring that, some consideration should be given to the oil pump not being fully seated on the flat spot in the crank. This could cause the pump to be crushed when the crank damper is installed.

Or maybe it's a DOA right out of the box.

Sounds like a timing cover removal is in your future either way. The good news is that you were careful and likely have a "repairable" situation. It stinks but is better than the alternative.

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Will definitely take a look at both those possibilities. Took the cover off yesterday, the chains look kind of dry so still suspecting the new pump but that's all I can really see at this point. Looks like I'll get a new pump and re-time everything:/

trinity_gt said:

I've heard of oil pump gears shattering on high RPM cars with incorrect crank dampers but that's clearly not the case here. I think the oil pump is coming out of yours for a look see. A few thoughts come to mind:

- check the oil pressure relief valve & spring are properly installed and not stuck
- take the back off the pump and inspect the rotors; on reassembly, pack it with petroleum jelly ("Vaseline"); this helps overcome any initial clearances in the pump and assists it in priming
- verify the oil pickup tube is not blocked

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Ya, we will take apart the new pump to inspect it once things are completely out. Is it wise to take a new pump apart and pack it like that because we won't be going in with the same pump unless we find another source of the problem? Will definitely double check clearence of the pickup tube