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Old 06-19-2005, 05:38 PM
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fuel pressure shut-off using oil sending unit?

I am looking for a common oil pressure sending unit that will ground out when the pressure drops below 4 PSI (dummy light system).
I would like to run this on me fuel line pressure side and allow it to ground my tach wire to kill the ignition system in the event of low pressure.

Is this workable? Does Anybody know of a sending unit that cycles at 4 psi?

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Old 06-19-2005, 07:05 PM
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Fuel Pressure???

Doc here,

I see all kinds of issues here..

FIRST, what Vehicle/Engine Combo are we dealing with here?

IS It Confuserized??

IS it a Standard HEI? Or other Hot Ign??

If you go grounding the tach, your headed (depending on what configuration you actually have) For ECM failure, Confuser Buffer/Driver Failure, or Coil Failure...or at least (if you have one,) Coil fuse blow outs..

If it is Confuserized .. and you ground the tach pulse (on GM 's anyway) You are HARD grounding the Reference pulse going back to the brain box..While it will Surely Stop the engine..Is hard on the Buffer / Driver inside the Cornfuzzer...And just maybe, Next time It won't Start again, Ever... (or until you replace the confuzzer)

The BEST set up..from your junk box...is as follows..get a 0 to 30 ohm pressure sender (pre 65 GM,you may have to experiment with up to 0 to 290 ohm senders to get your correct combo of 4 psi and enough resistance to fire /or /not fire the relay..), You may even be able to get a 4 PSI (or adjustable) pressure switch from an industrial Compressor supply house ,...and a relay...

Wire your Coil power and Coil through the relay...

To test or calibrate, put a copper shut off valve between the block and sender, pinch the valve down to 4 psi on the gauge..then adjust your total resistance for the relay coil (You may have to add resistors to get it exact..suggest 5 watt Ceramic's..starting at 100 ohm going up 50 ohms in each increment, you can get these at rat shack or Fry's..)To where the relay fires (or unfires, depending on how you actually hook it up) at that point..

Remove, or open the valve, and you should have it!

Be sure your Secondary Ignition is in tact and AFTER the relay..or it won't start on a zero psi engine until pressure is up..

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Old 06-24-2005, 09:38 AM
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Echlin makes them and I run one to cut the voltage to the pump. I don't have the part number but if you aks to look through the Echlin parts book they will have pics and specs on all the oil pressure sensors available. I do run this through a relay as well. Don't ask how I wired it though as I couldn't begin to expain it. I run a FAST EFI system as well as nitrous so it's looking at a few more things in addition to the oil pressure.
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