To answer the pressure question, full pressure is 3. My 420 idles at 1 1/2 to 2 and upon acceleration rides at 3 all the time. I concure that it is too much of a coincidence that the sensor happens to go out at the same time of your oil change.

Something is wrong and I would not drive it till it gets staightened out too avoid causing damage over something simple.

What kind of oil did you put in it?

And how many quarts did you use?

With the filter it should have been eight.

Hope This Helps!

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William
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1987 420 SEL - Like a fine wine only better with age