Quote:
Originally Posted by Bdc101
Andrew, what took the original motor out? I haven't logged in and checked this thread in a long time! Geez.
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BMW decided to make a variable output oil pump that's controlled by the DME.
They maximized efficiency over longevity and use just slightly too little oil pressure.
The problem is exacerbated by wide open throttle followed by immediate coasting; the pressure request will drop from ≈ 70 psi down to 40 psi when it should probably be more like 80 psi down to 50 psi.
https://f30.bimmerpost.com/forums/sh....php?t=2201790
Best write up on the topic on the internet^^^
So i was looking into finding a tuner nearby that could use the information in that thread to tune my car until i realized the output of the sensor is simply a linear relationship of pressure to voltage.
So I'm developing a very simple mod that will modify the pressure reading to the DME to trick the DME into thinking the pressure is lower and therefore boost the actual pressure.
I'm working on what the ratio will be but somewhere between 80 and 85%
Eg: at actual 40 psi tell the computer it's 40*0.8=32 and it'll boost to 40/0.8=50 psi. (seems a little high but minus atm pressure = 50-14.7=35.3).
I think i like 35 psi much better than 40-14.7=25.
When i get the details worked out i will be posting the fix of course!
The n55 motor uses about 50 psi cruising and 40 at idle and 68 i think maximum load.
This graph is a using some estimated values but in this example the sensor is outputting 2.45v which would be 49 psi but 2v is sent to the DME so it thinks it's 40 psi, it will boost the pressure until it actually is 49 psi.
(For those in the know, the oil pump on N55 is technically a volume controlled pump, but the feedback is pressure not volume).
My engine was not in good shape i was actually working on a trade with somebody to get a core engine that had spun bearings but only 110k miles, rebuild that engine but my car decided i should replace the motor about a year sooner than i planned.
For anybody that ends up in the same boat: if you have a place to do it and a helper it's not a terrible job just time consuming.
Cost about $5500 including all new coolant hoses and power steering lines. 20 hours or so labor.
About 30-50% the cost of a similar e70 so definitely worth the effort.
Oh: 5700 including the new motor mounts and catalytic converter brackets.
–awr–
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