4.3L Volvo Penta (1999) Oil Pressure switch goes Full Tilt when key is in ON position

MattBuss

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Jul 6, 2016
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I have seen several problems with oil pressure switches here, but none that are indicating full pressure when powered. Recently had to pull the engine to extract a broken starter bolt. Took the opportunity to replace the timing chain gasket / cover, oil pan gasket, plugs, plug wires, distributor cap/rotor, fuel filter, oil and oil filter. Now, that the engine is back in, as soon as I turn the key to the ON position, the oil pressure gauge max's out at high pressure ( not sure of value. will check later today). Based on other threads. if the lead is grounded, the switch will go to high pressure, so I assume, something is grounded. Can I assume if I disconnect the wire, the gauge will read ZERO?

How does the sending unit work? it must be based on resistance to ground...

1999 Larson 186 LXi
4.3L Volvo Penta GLX
 

alldodge

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Most marine gauges use 240 ohms (empty) and 40 ohms (full), so grounding the sender wire should peg the meter. Since you pulled the motor my guess is the wire is pinched somewhere. Look for the sender with only one wire (Think its Blue) on port side low on the block.
 

MattBuss

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Jul 6, 2016
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So, this is what i found today...
Sending unit ohms out at approx 250 Ohms. When applying pressure, the resistance decreases. All good, right? The sending unit looks to be good. When connected to the wiring harness, at the gauge, I get 86 Ohms. Wondering if my gauge has shorted.
For some odd reason, I could not getter wires off the gauge. More work to do I guess
 

bruceb58

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Mar 5, 2006
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You have to remove the wire at the gauge and measure the wire to ground. Measuring with the wire attached to the gauge doesn't tell you anything.
 

MattBuss

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Jul 6, 2016
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Looks like I got it. Gauge has gone bad. tried anew gauge, and seems to run properly. only thing is, always seem to be around 40 psi. seems high to me...
 

alldodge

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When cold (most are higher) not an issue and as for hot that is real good
 
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