Testing fuel pressure at rail
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Tuned
Joined: Mar 2018
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Testing fuel pressure at rail
I'm having some potential fuel delivery issues while towing with my Excursion and I want to check the fuel pressure at the rail with a test gauge. Does the hood being closed (partially, not fully latched) cause any pinching of the hose on the tester if I have the gauge routed up by the wiper to see while driving?
Also what pressure readings should I see with key on but engine off? In park at idle? Under load towing camper?
Thanks for any help you can provide.
Also what pressure readings should I see with key on but engine off? In park at idle? Under load towing camper?
Thanks for any help you can provide.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
I answered in your other thread, but just to be clear:
Fuel pressure, key on (after cycling it two or three times) and engine off, 38-40psi, engine idling, 28-30psi.
Engine running, with vacuum disconnected from the fuel pressure regulator (same as key on, engine off) 38-40psi.
Under load, the pressure should still read 38-40psi. If it drops off, you have a problem.
Fuel pressure, key on (after cycling it two or three times) and engine off, 38-40psi, engine idling, 28-30psi.
Engine running, with vacuum disconnected from the fuel pressure regulator (same as key on, engine off) 38-40psi.
Under load, the pressure should still read 38-40psi. If it drops off, you have a problem.
Thread Starter
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Tuned
Joined: Mar 2018
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Likes: 32
I answered in your other thread, but just to be clear:
Fuel pressure, key on (after cycling it two or three times) and engine off, 38-40psi, engine idling, 28-30psi.
Engine running, with vacuum disconnected from the fuel pressure regulator (same as key on, engine off) 38-40psi.
Under load, the pressure should still read 38-40psi. If it drops off, you have a problem.
Fuel pressure, key on (after cycling it two or three times) and engine off, 38-40psi, engine idling, 28-30psi.
Engine running, with vacuum disconnected from the fuel pressure regulator (same as key on, engine off) 38-40psi.
Under load, the pressure should still read 38-40psi. If it drops off, you have a problem.
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Tuned
Joined: Mar 2018
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Krewat, I was getting 32 psi key on, engine off but I didn't cycle it two or three times. I will try that tonight as well. As I believe i mentioned in the other thread, my max under load going up a steep hill was 38 psi. When I let off or was going downhill it dropped to low of 29. I will try the power brake tonight as well and report back.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
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From: Long Island USA
Yup, it's building the right pressure, and the "under load up a steep hill" at 39psi is just about right as well. Under load, vacuum drops off, so the fuel pressure regulator gets no vaccum, and it amps up to 38-40. Same thing when the engine isn't running, you should see 38-40. So you're right on the money with 39psi in both situations.
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