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What is this switch?
Hi,
I am attaching a pic or two of a switch (?) that is mounted to the top of the housing for my secondary fuel filter in my 1986 Prevost motorhome (an 8v92ta Detroit Diesel). It is leaking and I need to replace it. Can you identify it for me and tell me what it is, what the cost might be and where it is available?Paul Miller
paulfedex@hotmail.com
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14 Replies
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Paul Not for sure in your case but on the older Detroit’s it turned on the alternator Darrell
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We think it’s a sensor or solenoid to cut fuel off, maybe for when you turn off ignition???? I’ll have to look to serif ours has it, tomorrow.
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Looks like a pressure switch for fuel, maybe a low fuel pressure, or no fuel pressure light activated by that switch.
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I finally located this switch from Prevost parts. Seems they are having phone system problems, but I left a voicemail and they (Ed) called me back and we go the switch ordered.
I am still curious as to its function. The switch will take a while to arrive and I elected to tempoararily plug the hole left where I removed it. With the 2 wires disconnected the starter would not engage. I jumped them together and the engine cranked right up as normal. Later tonight I measured across the terminals of the old switch, in my lap, and found continuity between the terminals with (obviously) no pressure on the switch. This leaves me confused. Would the switch go open under higher pressure and why? Any guesses?
I included an image with a brief discription from the Prevost parts manual (Item 9, 56248). By the way, when it leaks as mine did it sprays fuel on top of the muffler below. Isn’t that exciting!
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Just a guess, but could it be to prevent starter engagement with the engine running? Some ignition switches will not go to the start position after being released until being cycled through the off position for this purpose.
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John that makes good sense to me.If it is the case,that would be a part to look at for a no crank concern, on that vintage anyway.Paul did you type the wrong part #?. Maybe still shook from fuel on the muffler!!
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I have this relay “pressure” switch on my 892’s on my boat and it does disable the starters if pressure is present. Pressure is present from the lift fuel pump when engine is running.
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I don’t have one on mine but that doesn’t help answer your question.
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Thanks for all the input from everyone. It makes sense that it is there to disable the starter when the engine is running. Certainly, you can believe it shook me to see the fuel spraying on the muffler. Fastest 40-ft sprint in my life!
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No rear stop switch? Most have rear start/stop controls.
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Probably correct, there are controls available at the rear. I have not used them and will now review their location.
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I thought I had this problem all sorted out after ordering the fuel pressure switch from Prevost parts. However, Ed from Prevost called me back to say they no longer have this part available. Does anyone know a source for this switch? Part # 562468
What would be the possible complications of running without it? It appears to disable the starter when the engine is running, but I read an older post somewhere suggesting it is somehow involved during an emergency shutdown. I don’t know the details.
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A detroit engine repair shop should have it in stock. When mine failed on my 892 on my boat I took it to Napa and they matched it up and I never looked back. Still working today.
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I would think that you could probably use an oil pressure warning light sending unit/switch. Normally closed and open at about 7 psi. The ones for early models are usually small and the connection is 1/8 pipe thread.
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