robt964

When the low pressure light comes on, where on the gauge is the oil temp? If the temp is too high the idle pressure will be much lower. If it is, are you sure the oil cooler circuit is flowing?

pi5tolpete

The last time I checked it, it was a 15 minute idle when the light came on and the oil temperature was not showing hot. The time before that, it was after a 4 minute drive when I pulled over and turned around. I don't feel it is an oiling cooling system issue, although I know I have work there too (read leaks, hoses, ballast, etc)

Mezger

Maybe they put wrong size main and/or rod bearings in when they overhauled the engine.
It's also possible that a bearing goes bad due to wrong installation.

pi5tolpete

So, I picked up my parts, swapped the senders, changed over the connectors, replaced the oring, installed and put everything back in place. I pulled the DME relay to allow a few cranks to pressurize the oil system, then stuck it back in and went for it. First run looked promising, 3 bar off the start. But it slowly began to drop, and finally I am back to where I was, but with a VDO brand sender, BradPenn green oil in the car, and a bit more knowledge of the back end of the beast. I went for a drive and the rpm tend to match the bar pressure pretty close. Warmed up the oil, thermostat opened, so I drove back and topped up the oil. Now drinking a beer and feeling sorry for myself. Next?

robt964

Sorry to here that. I guess it's time to make a few phone calls to some trusted and knowledgeable engine builders. Even visit them if they're not far. Discuss the possibilities and leave it with the person you feel most comfortable with.
Good luck and keep us updated.

pi5tolpete

Suggestions on a detailed C4 engine drop thread?

Rocket Rob

Sorry to hear the news. This is a good 964 C4 engine drop thread

https://rennlist.com/forums/964-1989...anny-drop.html

J richard

When you say the valve plunger fell right out, are you sure it was seated at the end of the bore? If there is a burr in the bore that keeps the valve from fully seating you may have it partially open all the time. Because it's spring loaded you don't really know if it's closed. The only way to tell would be to measure the depth of the bore and piston, slide the valve into place and confirm it's fully seated. A dowel marked to length will work. Given the symptoms I think that's your issue.

Even sloppy bearings will provide you with reasonable oil pressure, and pump volume will easily overcome that at higher rpm. A bad pump is pretty rare, a broken pickup tube maybe, a blown out galley plug or squirter. But unless it was left out you'd find something in the oil when you drained it. Any rod knock? A loose cap? You'd hear it. If you had a pressure pot you could see if the system holds pressure then you would know if you have a supply problem.

Hope for the best.

Steve Weiner-Rennsport Systems

I've seen a rash of worn/damaged 3.6 pumps lately due to trash circulating through the pump and it damaged the pressure side sufficiently to mandate replacement. I always disassemble the pumps to inspect the rotors and housings.

A loose cap comes apart right NOW and will make a lot of noise when this happens. Rod knock manifests itself under light load and heard at low & mid-throttle openings.

My best advice is not to run the engine until the problem is found as I've seen too many people continue to operate their cars while trying to find the source. At a certain point, the damage is done and can get quite expensive.

pi5tolpete

I am currently cold draining the oil one more time. I have borrowed a borescope to take a look at the inside of the engine sump. I've also removed the pressure relief valve yet again and I will look in there for any edges that the piston might be catching on. I'm going to lathe a dowel to the approximate diameter and measure the depth to the shoulder for the pressure relief valve. I'll then do the same thing with the pressure relief valve to see if it's hanging up earlier than that. Fingers crossed.

warmfuzzies

If memory serves, a long time ago there was a talk of failures of the piston crown oil squirters....?? If i understod correctly they open at around 3.5 bar, and should close some pressure later, but if they remain open can significantly lower the idle oil pressure.....From memory its from a P911 world article



Kevin.

pi5tolpete

Drained the oil again and inspected with the bore scope. Nothing to be found. Read in the manual that the spring should be 89mm. I was at 87mm so I shimmed with a washer to bring to spec. Saw what I could though the oil drain plug in the case. Just a nice shiny strainer on the pump. Torqued all back to 60 NM (45 ft lbs) and added back my filtered Brad Penn 20w-50 "green" oil. Restart, oil to 3 bar and slooooowly dropping. Warmed up the oil, and ..... Same thing. Idle is giving me the LP oil and idiot light. However, getting back to the driveway and under idle conditions, the light was off. Still too low a pressure but the light was off. No hope left really. I may drop a few quarts of oil and play with a mech gauge, but I'm pretty much resigned to an engine drop and rebuild.
Besides the safety relief valve and the mechanical gauge, is there anything else I can try?...

greg1990964

Not to ask a stupid question, but have you talked to the guy who built this motor? Does the guy have any morals and stand behind his work regardless of ownership change with little mileage on motor? Would a compression check help answer any questions? Why would oil pressure just drop like that. I am curious for an education in this matter. Does the car seem to still have power when driven?

J richard

Sorry to hear, I've never had this issue but may be worth a look at this point, chain tensioner plunger:

http://forums.pelicanparts.com/911-e...st6833861.html


hope for the best

robt964

Wow - what a collection of horror stories are found in that thread.