Ford intentionally faked-out the '87-up oil gauge to stop people from complaining about NORMAL gauge movements. With this mod (included at the factory on most vehicles with a gauge cluster, and integrated into '89-95 clusters), the ONLY normal movement of the needle is from low peg (key off, or key on-engine off, or engine running with no oil pressure) to mid-scale (engine running with 6psi or greater). Any OTHER needle movement indicates an ELECTRICAL fault - usually at the instrument cluster film circuit connector. If the needle drops to 0 with the engine running, the switch diaphragm is leaking from the oil side to the electrical side, which balances the pressure and makes the switch think there's no oil. If the engine is off long enough, that oil will leak out of the switch onto the ground, and it may show pressure next time the engine runs, until it fills up again.
On most Fords, the oil sender wire is Wh/R.
For other TSBs, check
here.
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TSB 88-05-14 Oil Pressure Gauge
Publication Date: MARCH 2, 1988
LIGHT TRUCK: 1987-88 F-SERIES, BRONCO
ISSUE: An oil pressure gauge that indicates an erratic or low reading when the engine oil pressure is within specification may be caused by the oil pressure sender (EOAZ-9278-A). The oil pressure sender may not work properly with the magnetic oil pressure gauge.
ACTION: To correct this, install a new design oil pressure switch and new design resistor wire assembly using the following service procedure. Refer to the oil pressure switch and resistor wire application chart for the correct service parts.
OIL PRESSURE SWITCH AND RESISTOR WIRE APPLICATION CHART
Engine Application Description Service Part No.
5.0L, 5.8L, 7.3L and 7.5L Oil Pressure Switch E6SZ-9278-A
4.9L Oil Pressure Switch E8TZ-9278-A
All Resistor Wire Assembly E6SZ-9F291-A
SERVICE PROCEDURE
1. Remove the existing oil pressure sender.
2. Install the new design oil pressure switch. Torque oil pressure switch to 10-18 lbs-ft (13-34 N-m).
3. Connect the female terminal end of the 20 ohm resister wire assembly to the oil pressure switch.
4. Connect the male terminal end of the 20 ohm resistor wire assembly to the vehicle wire harness.
PART NUMBER PART NAME
E6SZ-9278-A Oil Pressure Switch
E8TZ-9278-A Oil Pressure Switch
E6SZ-9F291-A Resistor Wire Assembly
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION DESCRIPTION TIME
880514A 0.4 Hr.
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This shows how to UNDO this on vehicles originally built with the 6psi switch, up to ~1995.
.
Later vehicles have the resistor built into the gauge head, so the gauge would have to be swapped out for an older one to make this work. The extension & sender will not fit with the factory oil cooler (which is useless anyway).
