No oil pressure? Except with cordless drill

[73 Black and Tan]

I could use a bit of help here... (73 240Z running L28 block).

I'm in the middle of a project and I'm having oil pressure issues that I haven't been able to diagnose.
Before my current project I would often get low oil pressure once it was warmed up and when at idle. Wasn't sure if it was the pump, the sensor, the engine, or something else. So I went to see if I could 'fix' this problem while doing some other work..
This current project has me doing the following: removing the timing cover to fix a leak, new oil pan (baffled Arizona Zcar), new hoses, new belts, new water pump, new oil pump internals (went to add a high flow version but turns out it was the same as I already had, thanks prior owner, installed the new stuff anyway), new oil pressure sensor, new oil filter, oil change with added oil for the new larger pan, and a coolant flush.

Issue: finished all of the above and whet for a drive. The oil pressure was higher than normal, not off the chart, but higher than before, near the end of the drive pressure was showing zero when at speed. I pulled over and did a visual and audible inspection. Nothing seen or heard.. limped it back home for further evaluation.
I got a mechanic oil pressure gauge, took out the oil pump shaft and reinstalled the pump to spin it with my cordless drill, it showed oil pressure!
But when I put it all back together, and pull the spark plugs and crank it still shows zero?!
I took a video of the shaft with the distributor off while I was cranking it to see if the shaft was actually engaged and spinning, it's spinning just fine.

Any ideas what's going on?

My fear is that my drill is spinning faster than the car rotates while cranking and that speed is needed to make pressure (probably not a good root cause to this).

Before I admit that the summer driving season is over and I pull the engine for internal issues, is there anything else I should/could look into?

Thanks in advance for any help.
-Will

 

[Bleach]

If the cam sounds normal while running, I would suspect the gauge in the dash is not accurate and that your oil pressure is fine.

The 280ZX seems to have a much more accurate oil pressure gauge than the older 240Z/280Z gauges. Using a separate mechanical pressure gauge for testing is a good idea.

 

With the L-series oil pumps, if you suspect they are working but not holding very high pressure then the oil relief spring inside them can be changed out. Maybe that is what you did when you put in new components.

[datzenmike]

Change the oil filter. If partly clogged it would restrict pressure at low speeds. There is a relief valve behind it in the block but I don't know what they are set to. 

 

I guess there's the possibility that an oil jet fell out causing a massive internal leak. Oil pressure would be very drastically affected at low speeds but as the leak would be constant the pump volume would increase as the engine revs up and so would the pressure. What did the mechanical gauge tell you at highway speeds vs. idle????? Normally I would expect over 20 idle and 55-60 at speed.

 

Probably everything is fine.  What I put on all my L series engines is the oil pump from either KA24E or KA24DE engine from a D21 Hardbody truck. Only the KA24E from the 240sx will work. Internally the rotors are 13% longer moving 13% more oil per turn. The relief spring pressure is about the same at 55-66 PSI but as the oil  supplied is a higher volume it can't bleed past the bearings as fast and the low pressure builds faster at a lower RPM. My hot idle oil pressure on my old L20B was 17 PSI. With no other change but a used KA wrecking yard oil pump it jumped to 29 PSI. I highly recommend one, even a new one.

 

 

 

 

 

[73 Black and Tan]

Thanks @Bleach, when running it didn't sound any better or worse that it has for the past 2 years I've had the car. I'm running a mechanical gauge now for diagnostic work but getting the same results as the in car gauge. 

 

@datzenmike, great thoughts. I have the higher flowing rotor running inside my old oil pump housing (so the same pressure spring). And I don't have a mechanical reading while driving, that is just a test setup while in the garage. I'd be nervous about a drive at this point due to the below update:

 

Update: I removed the oil filter and cracked the engine over for about 15 seconds.  To my surprise nothing came out. Not a drop.

 

This is making me think that my issue is prior to the pressure sensor, maybe it's either 

(1) I damaged the oil pickup tube when I installed the new pan and it is now too restrictive to allow enough oil to reach the pump under normal cranking speeds. Or 

(2) when I reinstalled the oil pump shaft is is somehow not engaging the pump, not sure if that's even possible.. but I can see the distributor spinning but I cannot verify the pump's actual actions.

 

I think my next step is to try to duplicate the results with the drill again.

 

Thoughts with this new info?

 

[datzenmike]

Pick up tube may be bent up and sucking air. Try temporarily adding a quart of oil. If this fixes the pressure problem then take apart and fix.

 

New pan???? Is it a stock pan or higher volume with a lower oil level? If oil lower it may uncover the oil pick up.

 

The larger oil pump rotors will not fit into the regular oil pump casting. It would have to be machined deeper. Easier to just replace with a KA pump.

[73 Black and Tan]

@datzenmike, yes a new deeper pan (Arizona Zcar, with baffles). I've added more oil and the dip stick is showing as good. But adding another quart to test is worth a try.. I'll also take the car off the Jack stands to be double sure I'm not sucking air into the pickup tube.

 

 

And FWIW the the story on the larger rotors is that I didn't know what the prior owner had installed when I bought a new high flow pump. When I went to install the new pump I realized that it was the same rotor as what I was already running.  To make sure that the pressure spring was what I needed and incase there were any issues with the existing rotor, I put the new rotor in the existing case. Hope that helps paint the picture. 

 

Thanks again! 

[banzai510(hainz)]

alwasy prime a pump that has not oil in it or make sure oil in it

next is a good filter.

 

get a KA oil pump. if you dont have it already.

 

 

Z cars use a spray bar?