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is your fuel pressure constant or does it fluctuate? 850

posted by  TomL on  Wed Jun 11 18:31 CST 2008
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last visit: Sun Jul 25 18:24 CST 2010
[RELATED]

<<<<<<<<< Pressure regulator is a sealed unit which is divided by a
diaphragm into 2 chambers (fuel and spring chambers). Fuel chamber
receives fuel through inlet side from injector fuel rail. Spring
chamber is connected to intake manifold vacuum. At idle, intake
manifold vacuum is high. Diaphragm is pulled back by intake manifold
vacuum. Any excessive fuel is returned to fuel tank. As throttle is
depressed, intake manifold vacuum decreases. Regulator spring
overcomes manifold vacuum, increasing fuel pressure>>>>>>

This is from the spec/repair info I have. Fuel pressure should be 43.5 psi with no vacuum.
The best way to test the pump and regulator is by jumping the relay contacts to turn the pump on then connect a vacuum pump to the regulator and watch the pressure decrease as the vacuum increases. I can't find the minimum pressure but I think it's around 35 psi at 20" vacuum.
You can test Fuel pump max pressure by pinching off the return line (momentarily) and see if the pressure goes higher than 43.5. If it does the pup is OK. I once had a poor connection at the pump and max pressure was only 38 psi with the return pinched off.
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE






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