[DW SD]

Gents-
Mysterious situation is going on with my newly rebuilt 3.6 and the idle oil pressure. Ollie's did the machine work and they seem stymied, too, as is the builder. This rebuild has about 300 miles, now. I'm running 20W-50 Castrol dyno oil and have changed it along with the filter after the cam break in and after a dyno session.

Here's some information about the pressure and data I've collected:

I have great oil pressure from off idle throughout the rev range. The pressure is at least 1 bar per 1k rpm. @ 3k rpm the pressure reads 3.2 to 3.3 bar and oil temp is verified ~ 215 degrees F. (I used a very accurate digital laboratory thermometer to calibrate the factory temp gauge).

Here's the issue:
The warm idle pressure is 7 to 7.5 psi, where both of my idiot light senders turn on below 12 psi. I checked the sender with a regulator to determine at what point the resistance went to zero in the idiot light sender.

We've taken a number of steps to verify information and remedy the issue:

1. replace the 993 pressure sender (it is both the idiot light and pressure sender.)

Result: No change at the gauge or the idiot light.

2. connect a large-face (4") and very accurate mechanical gauge to verify the factory oil pressure sender / gauge.

Result: The mechanical and factory dash gauges were in synch and calibrated.

3. we removed the oil pressure relief piston assemblies and took a close look. A burr was found in the bore which was causing scratches at the piston radius along the vertical axis. The burr was carefully removed with emery cloth.

Result: There was a small noticeable difference in that the pressure seemed to build up smoother as the engine reved (the gauge was less jumpy). I think the piston was sticking a bit. But the problem with low pressure at idle remained.

4. Finally, this morning, we changed all of the springs, both pistons and the shim in the pressure relief assembly.

Result: no change. pressure is great everywhere, but idle.

During the rebuild process, Ollie's polished and cleaned the crank and R&R'd the plugs. They also cleaned the case and R&R'ed all plugs and shuffle-pinned the case because they believed that the case was "walking" a bit. They also checked the align bore and cleaned the piston squirters. During the rebuild, the oil pump was inspected and cleaned and determined in excellent condition.

PS - When I drive around, I keep the idle up just a notch with my foot. The light extinguishes at 1200 rpm.

Here's my guess: maybe a pinched o-ring between the case and oil pump? OR maybe the main bearings are the wrong size?

The builder is more than willing to disassemble and troubleshoot. I'm just trying to get any other viewpoints / ideas before the motor is dropped and stripped again.

Any other thoughts? This engine runs great and dyno'd very well, too.

Thank you in advance!

Doug