Oil pressure is zero after engine drop and maintenance

I recently dropped the engine on my '02 C2 to perform the following maintenance items: 1. Replace cam followers (lifters). 2. Upgrade IMS with LNE bearing (preventative). 3. Replace AOS (preventative). 4. Replace clutch (was very worn). 5 Replaced transaxle gear oil. The main reason I performed this drop was to address a bad misfire on the number 6 cylinder that had become progressively worse, and an emerging misfire on #3. I performed the usual coil pack exchange and injector swap processes, but the misfires remained. The engine drop took roughly 10 hours due to my inexperience and caution, but as others have mentioned, would be much quicker the second time around. Many thanks to those who have performed this operation in the past and documented their tips and tricks. For example, removing the AC compressor was a 10 minute job thanks to such tips. I fired up the engine after the re-install and it seems to run fine, but I have no oil pressure. The most obvious culprit would be the oil pressure sensor, but it was working fine before the drop and I correctly re-installed the wires. Granted, the sensor could still be faulty, so troubleshooting recommendations are welcome. I also re-installed the oil scavenge pumps correctly. So, could it be the oil pump? Or something else? I did remove and re-install the oil pump plug and guide pin. Is it possible to not install this plug correctly? Needless to say, I am reluctant to crank the engine until I can be sure the engine lubrication is functioning properly. Any help is greatly appreciated. Mark

For a test to see if you have oil pressure you could always hook up a mechanical gauge where the sending unit is now, take out all the spark plugs so 1) it won't start and 2) there's no compression loading on any of the bearings, and spin it over with the starter to see if it builds pressure. If it has pressure, it's sensor/electrical, if no pressure, you've got to go back in to figure out why.

Well the first thing you need to determine if you have a mechanical issue or electric issue. Get a cheap mechanical oil pressure gauge and see if you get any pressure on cranking

Quotes source post: 9569756

Odds are high it is a sensor/electrical issue. If you ran the engine any time at all with no real oil pressure I think you'd know it. Not trying to be smart after the fact but whenever an engine is apart at least once before it is fired up it is best to spin the engine and verify the oil pump works and oil pressure develops. However from your post it doesn't read like you have the IMS out and the oil pump apart. That comment about the oil pump plug and guide pin though scares me, but I can't say if there's a wrong way to install these. If they can be installed the wrong way though...last thing touched and all that. Be sure too you got the scavage pumps installed in the right sides. The pumps are not interchangeable. If they are not installed correctly they will not scavage the oil from under the camshaft covers and this can empty the oil sump maybe to the point the oil pump sucks air. And then the engine has no oil pressure. As I'm sure someone else suggested removing the plugs, disabling the fuel pump (so no fuel gets injected) and spinning the engine just enough to confirm the oil pump is working and oil is flowing at some reasonable pressure at one of the main oil galleys is probably your 2nd step. The 1st step would be to very very thoroughly run through the oil pressure sensor/sensor wiring path to see if you can spot anything. Then double check your scavage pump work. Then just to be safe, do the oil pressure test. There's always 2 problems, unless the are are more than 2 problems or just 1 problem. Sincerely, Macster.

Macster, As always, a well reasoned approach. Since i did not mess with the IMS shaft on the crank side, or remove the oil pump, the likelihood of a pump key or gearing issue is pretty small. My first thought was the oil scavenge pumps, but I have quadruple checked the installation and the answer is always the same...correct in this case. After reviewing some documentation on how the oil pump works, particularly the high pressure relief mechanism, I am curious to know what happens if the pressure relief piston is missing or incorrectly installed. The piston rests on a spring which compresses under high oil pressure which causes some oil to shunt back to the sump (I assume), thus capping oil pressure. If the piston was missing or mis-positioned, I wonder if whatever oil is pumped would just get routed back into the sump, not allowing pressure to build in the engine? It would be pretty easy to remove the plug, spring and piston to check the theory but I am a little burnt out on 996 maintenance tonight(can you believe it?!), and I will check it in the morning. At any rate, it's a quick and easy start to the troubleshooting process, and as you mentioned, a very likely culprit because I messed with it. And, I have already double checked the sender wiring and harness for obvious issues, like reversing the wires or broken/damaged wires. If I can't ID an issue with the oil pump plug and piston, I will follow peavynation's advice and isolate to electrical or mechanical faults paths. BTW, I like the wisdom re. problems. They never end! Thanks much....Mark

Quotes source post: 9570153

LOL! that's some heavy wisdom there Macster. I wonder if there was even a flicker of life on your oil pressure gauge? It seems odd that you would have *no* pressure at all given the work you've done and if you had mixed up the scavenge pumps as Mac suggests you'd see pressure *until* the crankcase emptied. I guess the issue now is that you can't really run the engine until you're sure which makes troubleshooting that much more difficult. It's probably an sensor...good luck.