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Old 08-29-2017, 09:57 PM
gzus gzus is offline
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Default Fuel pressure

So I checked the fuel pressure on my Schlader valve or whatever the damn things called , and it reads 38psi with ignition on, engine off. Car manual says it's supposed to read at 40 with ignition on and engine off, and with engine on its supposed to go down 3-10 psi. Like wise when I turn the engine on it'd drop down to 28, and if I rev the engine the pressure only goes up about 1 or 2, (to about 29-30) for a quick second and then drops right back down to 28 even if I'm still on the gas pedal Revving. So my question is, could this 2 psi difference mean I have a bad fuel pump , or what ?

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1987 single cab ford ranger
4 cylinder
2.30 L
5 speed manual
2 wheel drive - rear
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Old 08-31-2017, 06:38 AM
tomw0 tomw0 is offline
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Join Date: Aug 2015
Posts: 875
Default Re: Fuel pressure

Your numbers are within 10% of the spec you quoted. Are you having any problem that would be caused by low pressure? If not, I'd chalk it up to variance in the pump and even the gauge. The gauge could be inaccurate also.
The regulator will 'bump' the pressure when you open the throttle, and vacuum in the intake manifold drops. That variance is used to give a boost to fuel spritz when the airflow in the intake increases. Air moves 'quicker' while it take liquid(more dense) a bit of time to catch-up to the air flow increase, so there will be a 'lean' bit of time until the fuel flow increases. Normal.
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