Replace oil pump?

[techspy]

Well, in my quest to track down the reson for low oil pressure readings, I am now considering replacing the oil pump. Just for info, the sender was already replaced with no change. I get about 3-4 bars of pressure when starting cold, and about 1.5 at cruising when warm. But at idle when warm it drops to the red zone, but immediatly goes back up with rpms. Anyway, before I consider an engine teardown to look for any serious problems, I want to eliminate everything else.
So, anyone have experience with replacing/rebuilding the oil pump? What parts should I order? I guess I should also rebuild the chargecooler pump since I will have that taken apart as well..or will I? I have the manual and it seems pretty straigh forward. Also, does anyone know a place close to the stock oil pressure sensor that I can install an additional sensor for a temporary digital guage?

Thanks
John
94 S4
http://hometown.aol.com/oneshotcop/myhomepage/profile.html

[rlearp]

Have you checked your oil pressure with a real pressure guage - i.e., non-VDO dash gauge? Before I did anything this would be my first action. Drop my a shop and have them do it for you if you don't have one but even if you paid $6o to have it done it'd beat a tear down for naught if all is well.

[techspy]

The plan is to purhase a digital guage and sensor and install it temporarily to see whats up. I am not sure where to install the new sensor though. I don't think the vdo guage is the prob. The tell tale light and guage are in sync, and I have changed the sending unit with no change. However, I plan on connecting a newer/more accurate guage and sender before getting too carried away.

John
94 S4

[rlearp]

I can't remember if the tale-tale and the gauge are on the same sensor or not. If they are then of course they'll be close. At any rate, you should be able to plug a unit into where the old sensor is and measure.

>> Edited by rlearp on Monday 26th April 03:03

[dr.hess]

Acording to the schematic, the idiot light and the guage are on the same transducer, but different circuits within the transducer. I suppose it would be possible for the transducer to be bad if it is spring loaded or something, I don't know. Have not taken one apart to see how it works. I would definetly replace the transducer and/or try a different system as you are trying to do before tearing into the motor.

Dr.Hess

[techspy]

When I mentioned sensor, I was speaking of the transducer as it is called in the manual. It has a ground connection, and a connection that feeds the signal to the gauge and the tell tale through the rpm switch. So, the tranducer/sending unit/sensor has been replaced.
I also went on the VDO website and found the procedure to test the impendence range of the gauge. The guage shows maximum with a 180 ohm load, and 0 at a 0 ohm load. I tested this with a potentiometer. Question is, what impedence is the transducer/sending unit/sensor supposed to put out at what pressure? I may try calling VDO this week to see if they can shed some light. In the mean time, I am going to go ahead and fit a new sending unit and gauge for testing purposes. Using the existing sending unit/transducer wouldn't be reliable at this point.

John
94 S4

[rlearp]

I would avoid all VDO and OEM stuff at this point and just get a dirt simple mechanical oil pressure gauge. Plug that thing into where the sender is and read pressure - simple, reliable, and will tell you what you need to know.

[LotusSE89]

A low oil pressure reading may not be a problem with the sender or the pump. I have seen low oil pressure readings with bad bearings on the connecting rods.

Travis
Vulcan Grey 89SE