I do not have an oil pressure switch above the oil filter in the back of the engine block, or on the V-Tec solenoid (there is a bolt where the pressure switch usually goes).

Does anyone know how oil pressure is monitored on these engines?

Thanks. John

 

The oil pressure switch is not directly above the oil filter, it is above the metal coolant pipe and closer to the intake manifold. I had to reach above and remove it by feel, because it wasn't easy to see. It will have a one wire connector going to it with a "rubber" boot that feels like plastic.

To answer your question, the PCM does not monitor oil pressure. That switch will turn on the oil pressure light in your car when the oil pressure gets below a certain point. That is why it is recommended to check the oil level on the dipstick periodically. I usually check when I fill up the tank on my car.

 

PAhonda is correct.

To add some more info.:

The oil pressure switch is a normally closed type of switch and is grounded at the engine block where it is attached to. When the switch contacts open, then ground is removed.

The wire go to the instrument gauge oil pressure indicator; however, the integrated control unit (located in the under-dash fuse box) is also part of the oil pressure wire circuit going to the gauge.

This is how the circuit works:
The low oil pressure indicator light works in two ways: it flashes continuously following a momentary loss of pressure, or it goes on and stays on with a complete loss of engine oil pressure.

When the engine first starts, before its oil pressure rises above 4.3 psi, voltage is applied to the closed and grounded engine oil pressure switch and the light comes on to test the bulb.

With the engine running, voltage is applied at the WHT/BLU wire of the integrated control unit. With normal engine oil pressure, the engine oil pressure switch is open and the low oil pressure indicator light does not come on. If the engine oil pressure switch closes momentarily (more than 0.5 second) but then opens again, the YEL/RED wire at the integrated control unit will sense ground through the switch. The integrated control unit will then provide and remove ground for the low oil pressure indicator light through the YEL/RED wire. The light will flash on and off until you turn the ignition switch off. The flashing feature will not work until 30 seconds after initial voltage is applied to the WHT/BLU wire of the oil pressure indicator flasher circuit. This delay keeps the low oil pressure indicator light from coming on during engine warmup.

If engine oil pressure falls below 4.3 psi and does not increase, the engine oil pressure switch will stay closed. The low oil pressure indicator light will then come on and stay on.

 

Found it.

Boy, it's really tucked away in there! But good to know where it is.

Also, thanks for the description of it's operation ... good to know in case I ever need to troubleshoot this thing.

For now my interest was in trying to determine if my V-Tec is working -- so at least for now I know that I've got oil pressure

Actually, I have a followup question -- is the min oil pressure allowed by the oil pressure switch enough to engage the V-Tec synchonizing pistons?

Thanks. John

 

1. As shown in the attached image at the bottom, the control system for VTEC constantly monitors the changes in engine status such as load, rpm, and vehicle speed.

Valve timing change conditions:
Engine Speed: 2,300 ~ 3,200 rpm (depending on manifold pressure)
Vehicle Speed: 6.2 mph (10 km/h) or faster
Engine Coolant Temperature: 50 degrees F (10 degrees C) or higher
Engine Load: Judged by intake manifold negative pressure

2. The VTEC solenoid valve is used to apply oil pressure to the variable timing system. The variable timing system uses the re-routed oil pressure to the rocker arm pistons.

The VTEC oil pressure switch was use to let the ECM know if oil pressure was applied to the VTEC system. See this link for some additional info:
http://www.google.com/url?sa=t&rct=j...89381419,d.cGU

3. On the 94-95 Accords with VTEC, it had a VTEC solenoid valve and a VTEC oil pressure switch.

On the 96-97 Accords with VTEC, it had a VTEC solenoid valve; but, no VTEC oil pressure switch.

Accords after 1997 added back a VTEC oil pressure switch though.

4. The oil pressure switch on the back of the engine block that goes to the gauge oil pressure indicator does not have anything to do with the VTEC control system; the wire does not go to the ECM. Even if the oil pressure gauge light was not on or blinking to indicate low oil pressure, that does not necessarily mean oil pressure was okay at the rocker arm for the VTEC system.

Generally, the VTEC oil pressure switch on Hondas are located near the rocker arm.

 

So the 96-97 V-tec systems don't use oil pressure as a control input? I still wonder then what it takes to move those pistons? Seems like you would need something substantial. Since Honda removed the pressure switch I would assume they were thinking that whatever oil pressure is normally in the engine is sufficient enough to operate the V-Tec pistons. Or did they add the pressure switch back after realizing that it wasn't sufficient?