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Should The Fuel Line Have Pressure When???


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#1
ron2011

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i have posted a few topics but this is one i believe may be the source of all my problems today i tried to start my car and wouldnt even run at an idle . so i stuck a key in the place where u would put the pressure tester at and nothing came out ??? my question is isnt the pump suupose to prrime the line while the engine is turning over so if no gas come out could the be the relay fuel filter and or pump? and does the line have pressure while u are cranking the engine?

#2
djdevon3

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There is actually a procedure for pressure testing where the fuel lines must hold pressure for at least a certain amount of time. I'm not going to guess on the amount of time. I know it's an hour or less. I believe it's supposed to hold pressure indefinitely using the 2 way check valve near the gas tank. After that the fuel evap system might slowly purge the line of pressure (less desirable and still within spec) but it must hold pressure for at the very least I'll say 5 minutes. Normally a little pressure loss isn't a big deal because when you turn the key to the ON position the fuel pump immediately re-pressurizes the line right before you try to START. If you get no pressure while the key is in the ON position then you've got fuel pressure problems for sure. ;) Turn the key to ON (not running) and listen very carefully for the fuel pump to prime. It should sounds like a whirring noise coming from near the gas cap area. It's easier if you have a friend help. No sound means a bad fuel pump relay or fuel pump.

Unless you're Fade26 and can fix it yourself using a bicycle tube and a tree-stump-for-a-scissor-jack then I'd recommend you take it to a mechanic who can diagnose the issue and possibly drop the tank to replace your fuel pump. Remember this is just the internet and we can only go on the information you provide. We are not certified mechanics only owner-to-owner support. Good luck.

#3
ron2011

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lol i always do my own fixin i was just curious about the fuel pressure i am going to start at the filter and see if its either the filter pump relay or the pressure regulator . snd thanks for any info

#4
fiberglassworks

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to test the relay get a multimeter, turn the key to "run" and then stick the probes in the two terminals that should get power during operation, if there is no voltage there then you have a wiring problem, if you are getting voltage there then replace the relay and test the terminals that run to the fuel pump relay during operation, if you get voltage there as well then your fuel pump is bad and will need replaced


sorry i dont know the colors, nor which terminals to check here

#5
ron2011

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thank you i will try that . i am just glad i think i figured out my problem i thought it was something a little more serious i have to to much time and energy into my car lol . and truthfully i love my mazda .

#6
ron2011

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and another dumb question about fuel pump issues i pulled of the fuel line to the fuel rail and when u turn the key to the on position i was under the impression that it would prime the line well when i turn on the key nothing happens . but when i crank it i get gas that makes no sense to me . ?????? i havent taken the filter of yet i will do that today but any input would help .

#7
fiberglassworks

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i would say that your fuel pump relay is probably shot

#8
ron2011

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could a clogged filter cuase the line not to prime ? and then when u crank the engine it would build enough pressur eto break through the clogg ima change it tonight and see what happens

#9
djdevon3

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Do a search on how the fuel pressure regulator operates.

#10
4thgenceli

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I don't have much experience with Mazda FI systems, so take this with a grain of salt.

Older fuel systems (carb'd systems) when you turn the key 'ON' the pump should kick on and prime/pressurize the system. That's why sometimes with a carb'd motor that's not quite adjusted right you would have to pump the gas once or twice to get air out of the line & fuel into the combustion chamber(s). With fuel injected systems, you don't need to pump anything because the computer opens/closes each injector accordingly (thus getting air (if present, usually not) out and fuel into the combustion chambers).

The way my Toyota's fuel system works is:

Put the key in the ignition and turn to 'ON' position --> no power to the fuel pump
Put the key in the ignition and turn to 'START' position --> power to the fuel pump

Now I can bridge a few terminals (well used to before I swapped out the motor) and that would turn the pump on with the key in the 'ON' position. So while you say you don't have power when the key is in the 'ON' position, you may want to check for power when trying to start the motor.

Also the fuel pressure readings vary from car to car, model to model. Usually though you after you turn off the motor, it should stay over a certain PSI reading for at least 5 minutes, then slowly drop off.

#11
ron2011

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thats what i thought but after turning the key to all the way foward a few times and cranking still no fuel in the line . i will post after work my results with just changing the filter .

#12
4thgenceli

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Another easy thing to troubleshoot what is wrong (instead of throwing parts at it) is to disconnect the fuel line at the tank (or before the filter). Once it's disconnected, try to start the car. If fuel comes out, your pump is fine and it's something else (filter/etc). If no fuel, then your pump is muerto.

#13
ron2011

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i thought of that but if my pump is weak that could also cuase a potential problem and i didnt think of the fuel pump when i started having issues lol never crossed my mind . so i did my 02 sensor maf wires coil pack lol .so now i am to this point if the filter is badly clogged or weak pump could be choking me out and cuasing all the symptons i am havin . one small piece at a time my car has over 200000 miles on it and i have no idea when the last time the pump/filter was changed.

#14
djdevon3

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Filter is a cheap part too and never hurts to replace it. Let us know how the filter change goes.

#15
ron2011

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i took the filter off and well i cranked it and needless to say when i cranked the motor hardly any gas came out even though the pumped kicked on . i listened to it ti sounds weak lol . so i am hoping that my be the problem . so there is my weekend project .i will also be changing my control arm . i went to pull apart for a couple parts they have a 2001 mazda 626 i noticed that the intake is different ? did they change some parts from 98 to 2001 and would of any of the vacum lines work on a 98 ?




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