1989 930 oil pressure or gauge issue?
Okay, I need some insights and opinions. I have a 1989 911 Turbo, all stock, 95K miles. I bought it 15 years ago with 50K milkes on it. I don't race it or abuse it and rarely take it over 7000 rpms.
For the past however-many-years (can't remember, it's been so long....) the oil pressure gauge has "flickered" about a reading, especially before the oil gets fully warmed and at idle speeds. The needle bounces around a reading. However, the needle always responded in a normal expected manner: 5+ bars at cold start up, and then gradually reducing to 1+ bar at idle when warmed, and always following engine rpms up and down. Upon accelleration, the needle would stop its flicker and it would generally return to flickering as load was taken off the engine or upon return to idle. Even when fully warm, the gauge would respond as normal, pegging 5+ under very hard accel and/or higher rpms. The needle would move as expected, i.e. about 1 bar per 1000 rpm's, up and down the scale, with the only problem being the needle bounce/flicker...
So it was always a minor annoyance issue to me, as the guage responded as I would expect it should to engine rpms/normal oil pressure.
Okay, so I recently stop by a local independent Porsche service center and ask about this situation, inquiring about the price of a new sender (as I thought that was probably the problem) and the owner says "oh no, it's a loose wire at the sender, just make sure it's tight." Sounds reasonable. So I take the wire off, clean the sending unit terminal and used a small round file to clean inside the wire connector plug, and push it back on. It's nice and tight. I go start it up and now the flicker is gone! BUT.....
The guage doesn't flicker, but it doesn't respond to engine rpms, either. When cold, it reads a rock steady 2 bar, and then s-l-o-w-l-y drops to 1 bar at idle and VERY slowly follows engine rpm up to a max of 2+ bar, even when the engine is at 5000+ rpms. So I take it back to the shop and say "fix it"---still figuring it's a bad sending unit or guage. He calls back and says he's replaced the sending unit, tested the continuity of the wire to the gauge, swapped another gauge in and out, and nothing changes. He even says he put a mechanical guage into the sending unit port and that there actually is very low oil pressure...as in "almost none". He says that either the oil pump is wasted or the engine bearings are worn out. Huh??? He says that he shimmed the oil pressure relief valve with three shims (?) and has gotten the oil pressure up to about 3 bar at cold idle, but that's as far as he can go. It's had a fresh oil change and filter, no smoke, no knock, no noise, no debris in the oil or on the magnetic drain plug.
Besides tearing into the engine, does anyone have any other ideas or similar experience? I find it hard to imagine that this engine has such significant problems considering that until I pulled that wire off, the gauge responded EXACTLY as it should if everything was okay (I'm 45 years old and have driven cars with real oil pressure guages, both electrical and mechnical, all my life).
Anyone's help is most appreciated!