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Old 09-29-2013, 03:34 AM   #1
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Default Carbed 5.0L stalls at idle. Oil pressure safety switch? How to replace?

Can anyone advise on how to test & replace an oil pump safety switch?
3000SCR's port side 5.0L is stalling at idle. Runs very well above 2000 rpms. As soon as I drop the throttle down it stalls out. The yard mechanic serviced the carb (float, etc) for $100.00 but no change. I've read a lot about it possibly being the oil pressure safety switch cutting power to the fuel pump if the switch is shot. Oil pressure is ok & normal on the guage when running. Upon finding what I think is the switch near the oil filter, I pulled the 2 purplish wires off & put them back on to ensure good contact. No change. Cant seem figure out how it comes off the engine in order to replace it... (Also checked th safety lanyard which is also in tact & correctly in place.) Though it may be an easy & cheap next step to check out the op switch.
Anyone experience this issue & is it an easy DIY fix to test or replace it?
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Old 09-29-2013, 11:48 AM   #2
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Max you can pull te 2 wires off the OP switch and jumper them together. Make a short jumper of the same guage wire and put blade connectors on it same as on switch. If this allows the engine to run then replace switch.

Just to verify your engine does have an electric fuel pump, correct?

The switch screws onto the engine. There should be a flat spot on it for a open end wrench. If not use channel locks.

Let us know what you find.
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Old 09-29-2013, 01:35 PM   #3
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If you don't have one already, this is good time to get a multimeter and learn how to do a continuity check. Easy to do and well worth your time to learn. The OP switch is particularly simple to check and you will save yourself time, money, and aggravation.
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Old 09-29-2013, 03:16 PM   #4
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[QUOTE=mmwjr;30225]Max you can pull te 2 wires off the OP switch and jumper them together. Make a short jumper of the same guage wire and put blade connectors on it same as on switch. If this allows the engine to run then replace switch.

Just to verify your engine does have an electric fuel pump, correct?

The switch screws onto the engine. There should be a flat spot on it for a open end wrench. If not use channel locks.

Let us know what you find.[

re Wires: I wanted to jump but wasn't sure how do to the blade connectors as you mention. I checked for corrosion to but seemed ok from what I could tell. Would it be easier to check with a volt meter?

re Fuel Pump: I'm actually not sure if its an electric fuel pump or not. How can I verify this?
Thanks-
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Old 09-29-2013, 03:22 PM   #5
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Sounds like a good idea. I'm assuming I'd need to have the ignition just turned to start/on, doesn't need to be cranking over while checking, & then check the wires correct?

Thanks-
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Old 09-29-2013, 04:20 PM   #6
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O to make the jumper you need a wire crimper tha came be bought at any home store (lowes, home depot, ...) or marine store (westmarine, ...). The crimper has color dots that tell you what crimp slot to use depending on the lug size in this case blades. You can buy a kit at any of the places I mentioned that included lugs and the tool. See link for an example

http://www.westmarine.com/webapp/wcs...classNum=50569
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Old 09-29-2013, 04:25 PM   #7
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A mechanical fuel pump will be mounted on the starboard side of engine near fuel filter. An electric fuel pump will be mounted on the front of the engine just behind the pullies. It will be about the height of a soda can and 1/2 the diameter.

To test the switch no power is required. Pull the 2 wire off it set the meter to ohms. Touch each terminal on the switch with one of the meter's leads. Should be zero ohms. If it is the switch based on what you told us I would assume it has a weak spring and is open ( no reading on meter) at low rpms and closes ( zero ohms) at higher rpm.
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Old 09-29-2013, 04:28 PM   #8
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Here is what amechancial pumps looks like

http://www.westmarine.com/webapp/wcs...classNum=61533

Here is what an electric pump looks like

http://www.westmarine.com/webapp/wcs...classNum=61533
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Old 09-29-2013, 07:56 PM   #9
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I would believe a gasket or vacuum leak.

Since the engine run at 2000 rpm, its not a fuel issues, nor a oil pressure related.

But, if your sucking more air then fuel, then its a vacuum or air leak thru the carburetor base gasket, or some other hose.

If the floats where done, and not a full carburetor rebuild, then the gasket will need to be changed.

2000 rpm is pretty forgiving with the engine vacuum, idling on a leak fuel mixture would kill your engine, which s idling at 800 rpm.
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Old 09-29-2013, 09:46 PM   #10
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Thanks Mike.. Very helpful.. I have find out which one I have. If my fuel pump is manual I'm assuming it will eliminate the OP as a possible cause for stalling, right?
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