How to check fuel pressure - Page 2 - Nissan Sentra Forum - B15, B16 and B17 Sentra Forums
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post #16 of 22 Old 09-30-2010, 11:39 AM
timeattack85
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I'm not saying this is the answer because I CAN be wrong, but those readings are not within specifications. I'm led to believe that the one way check valve (usually within the fuel pump is defective). Try replacing the fuel pump, and let me know what happens.
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post #17 of 22 Old 09-30-2010, 03:26 PM
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Originally Posted by Jugo Driver#1 View Post
Ok, so our cars are not supposed to hold any pressure in the fuel system after the car is shut off?

i wouldnt thinks so. why else would the pump prime the system if it held pressure when the car was off.

if its jammed-force it, if it breaksin the process- it needed to be fixed anyway
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post #18 of 22 Old 09-30-2010, 04:34 PM Thread Starter
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Most cars that I've worked on will hold fuel pressure for a pretty long time. Mostly all fuel injected cars will prime the fuel lines with the key on in order to remove any air that might be in the lines from drain back that may have occured. Does anybody know the specification on how long our fuel system should hold pressure 10 minutes or so?

02 Molten Silver Spec V
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post #19 of 22 Old 09-30-2010, 04:41 PM
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I don't know EXACTLY how long it'll hold pressure, and at what pressure, but I did my fuel pump hours after parking it at my parents, and it seemed pretty darn pressurized to me. Keep in mind we do not have a return fuel line, so I'd imagine it would take quite some time for it all to drain back into the tank...
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post #20 of 22 Old 09-30-2010, 06:42 PM
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It should hold fuel pressure for a quite a bit. I admit, I've never really tested it longer than a minute or two, but on average, it drops about 10psi in 2 minutes and seems to stop.

Fuel is actually not supposed to drain back into the tank in modern vehicles, it's supposed to retain as much of it as possible. The one-way check valve prevents drain-back from occuring so that you can start it right up, the next time you go to start it. Also, to prevent vapor lock from occuring.

***Also, when you go to change the fuel pump, please be careful. I've seen too many accidents with fuel tanks, and it's not pretty. Make sure you use compressed air around the tank to ensure no debris falls into the tank, and if you must use a hammer and chisel to loosen it, make sure you are not hitting metal to metal. Bronze and copper head hammers work great too.
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post #21 of 22 Old 09-30-2010, 07:14 PM
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^^^
Good Lord. Why would you need to hit your tank with a hammer??!?!

But yeah, no smoking when changing out your fuel pump!
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post #22 of 22 Old 10-01-2010, 08:06 AM
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^^^
I guess you're not from an area that gets a lot of snow. Here in Chicago, by the time a vehicle comes in for a fuel pump, the ring that holds it down gets extremely rusted. In order to get it out, you need to use a chisel and a hammer to slide it around. That's what I meant. I say this, assuming that everyone realizes that a flathead screwdriver is not a chisel! Chisels are usually metal at both ends. I never suggested hitting the fuel tank. As for hitting the actual tank with a hammer, that is a quick way to diagnose a fuel pump failure in the field as well. When a fuel pump fails and the vehicle does not start, after confirming a fuel problem, the first thing to do is to get under the vehicle and hit the tank with a hammer while someone else is turning the ignition, in order to get the fuel pump to work. This is a backyard bob diagnosis, but in the field, time is money, and it works 95% of the time.
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