Jim Grant's Tech Tips
'91 Mercury Crown Vic, Low Oil Pressure
Q:
I have a '91 Crown
Vic with 122k on it. Lately the oil pressure light comes on, but only
when the car is FULLY warmed up and idling while stopped. I'm pretty sure
the pressure is low because I can hear a little rattling in the lifter
department. It seems like the problem may be what controls the idle at
high operating temperature. For example, if I take all load off the engine:
turn off A/C and put transmission in park, the idle pops right back to
a level which provides adequate pressure. It will even stall out while
idling at a red light as the idle speed gets too low. Do you have any
ideas?...Jay
A:
There are a couple
of items you should have checked. The idle speed is computer controlled
and should not be dropping to the level that would create a stalling condition.
The likely cause is a failed idle air control valve. It doesn’t take
long to diagnose a failed idle air control valve. Too low of an engine
idle speed on a vehicle of the age/mileage could allow oil pressure to
drop to the warning level. If the problem remains after the idle speed
is corrected then have a mechanical oil gauge installed to check the engine
oil pressure readings. This would aid in determining if your problem is
a serious one or just age showing up. Also, don’t be afraid to change
the oil from a 5w-30 to a 10w-30 or 40. A little heavier oil can make
a difference in preventing metal to metal contact in older engines.
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