On my M111 engine you can sometimes see the oil pressure guage fluctuate when the timing changes - I think that's because the timing solenoid uses engine oil pressure to act hydraulically on the camshaft drive advance mechanism.

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Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)