Over Fuel Valve (OFV) operation

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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Location: Canada


Post by Nissan_Ranger »

I've been going with the stock set-up less the OFV valve and have not had a problem since I punched it out. YMMV

The old 'six gun' was as popular as the cell phone in its time and just as annoying when it went off in the Theater.
Tracteur Tom
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Post by Tracteur Tom »

Thanks N R. The problem with that is you will not create a pressure in the IP fuel chamber as it is open to the return line without a restriction. Yes it will work and is the set up on many a diesel of old I've looked at. But, a little pressure in the IP fuel supply line (1-2 bar) is good for stability and air pocket release I'd have thought.

I think one of the reason's Philip modified his set-up was because he thought he had too high a pressure. It wasn't clear to me from the postings as to whether the problem was caused by a faulty OFV or the updated lift pump he had. I wonder if you could modify the OFV with a slightly larger orifice, this should bring the pressure down ?
Tracteur Tom
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Location: France


Post by Tracteur Tom »

I found this thread and though it would be good to reference it here:


seems Philip did have an answer after all :D
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Re: Over Fuel Valve (OFV) operation


Post by Skeeter2u »

I think the air comes from the fuel discharge line, that goes back to the tank from the filter housing; it is the only line that is open to the atmosphere, as it dumps in the tank with no line into the fuel. I have connected the return line and the discharge line from the filter housing, and pluged the two ports on the filter housing. I have been able to drive with the tank below 1/8th, and previously it would quit if half or below. So far so good. I am now unable to reduce the fuel pressure form the delivery pump, but so far have not blown any hoses.
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