yo,
Good!
EEC's rearely are the issue, but in this Bronco...
The oil pressgauge operates through a pressure activated switch. and in not a true gauge unless that prev owner(s) or "mechanic" swapped in a true gauge & sender or did a little mod to the ckt.
When the engine is started engine oil pressure closes the switch, providing a ground circuit for the gauge coil. Current flow through the gauge coil to ground causes the primary magnet and pointer to rotate, providing an oil pressure reading on the dial face
The oil pressure switch controls the magnetic oil pressure gauge's pointer position. The oil pressure switch closes under normal engine operating conditions (oil pressure above 42 kPa [6 lb/sq in]). The oil pressure switch opens with the engine (6007) off and no oil pressure.
&
These vehicles do not really have what we would call a conventional oil pressure gauge. The sending unit that is used is not a variable resistance unit. It is merely an On-Off switch. There is a fixed resistance in the dash gauge that will cause the needle to deflect a certain amount regardless of the actual oil pressure. So, it does not matter how high or low the pressure, in any case, the gauge will read the same, as long as there is sufficient oil pressure to close the switch. Any time there is a question of oil pressure, the first step is to ignore what the gauge reads and verify the oil pressure with a mechanical gauge. Once you have eliminated a mechanical problem, then concentrate on the electrical part. On these vehicles, if you have eliminated the mechanical problem, and, have replaced the oil pressure sender with no improvement in the gauge reading, Ford recommends that you use a 20 ohm resistor in line between the sending unit and the gauge. Installation of the resistor will stabilize the gauge reading and eliminate the customer concern..." MIESK5 Note, see how to install the resistor in Link below
Mod to Actual PSI "...short R in PCB..." in 87-88 F series trucks and Broncos
Source: by Mike & Debbie
http://www.rowand.net/Shop/Tech/FordOilPressureGaugeFix.htm
OR
Installation, Sunpro Mechanical, w/T for stock gauge Source: by Sixlitre (Malcolm H, Eddie Bauer) at
http://www.supermotors.net/registry/4970/22156
Source: by Bob R
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re; "...when I accelerate on roadway, the HVAC temporarily moves airflow to defroster and then eventually switches back to selected vents. Checked vacuum lines, all good..."
most often it is a vacuum leak in line to Outside Recirculate Door Vacuum Motor (originally a White vac hose) or the line to and including the door "vacuum motors"
The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit.
Or could be @ other vac controlled / operated components such as PCV line, emission ckt, cruise control if equipped
see more @
http://broncozone.com/topic/22770-low-idle/
Outside Recirculate Door Vacuum Motor pic in an 89; Shiny piece in upper left
Source: by Booba5185 (Matt) at
http://i205.photobucket.com/albums/bb57/irpancake1/bronco/cid_642.jpg
Floor/Defrost, Panel, Temperature Blend (cable controlled), Outside Recirculate Air Doors & Vacuum Motors Location Diagram & Overview in an 86; from Electrical and Vacuum Troubleshooting Manual (EVTM) Partial, Bronco for 86; see Pages 141, 142 & 143 should be = to your year
Source: by Chris B (Blue, bronco boy) at
http://chrisb.users.superford.org/Bronco/Misc/