Checking fuel pressure

[LA_phantom_240]

I think I've narrowed my bogging, misfire problem to low fuel pressure. Since I first posted my problem, now I'm having a hard time starting it. When it does start, it runs really shitty for about 10 seconds and if I try to give it gas it dies. If I let it sit for a few seconds, idle will come up to normal and all is good.

Also, when giving it a good bit of throttle driving down the road, it feels like it has very little power and starts misfiring and backfiring through the exhaust. Last night, I heard a really high pitched whine/screech coming from behind the seat for a couple seconds... so I think my pump may be on its way out, or having to work its ass off because of a bad regulator or something.

How do I go about checking pressure? I don't see any port I can tap into for a gauge, like everyone who knows cars has told me there should be.

[LA_phantom_240]

Is idle supposed to change when I unplug the regulator's vacuum line?

[WoolyS14DET]

Is idle supposed to change when I unplug the regulator's vacuum line?


Def check you pump !! Sounds fuel related!! If your spark plugs are old they might be a problem as well. If you leave that vacume line open when you unplug it yes it will change the idle.
If you have a stock regulator you need to put a pressure gauge on the feed line after the filter to see what fuel pressure your at

[HalveBlue]

To check your fuel pressure you need to start by relieving the fuel pressure.

Take out the fuse for the fuel pump and crank your car several times.

Then take off the Fuel In line. Make sure you wrap a cloth or something around it to catch the rest of the fuel that'll spill out.

Attach a fuel pressure gauge inline on the fuel line.

Reinstall everything and turn on your car. You should now be able to monitor your fuel pressure.

Good Luck!

[UNISA JECS]

Is idle supposed to change when I unplug the regulator's vacuum line?

It could and usually does a lil bit, because one, you now have a vacuum leak, two you are injecting more fuel.

[LA_phantom_240]

It didn't change my idle. At all.

[surreybc]

this tells you how to measure fuel pressure on a 240sx. just read the instructions that come with the gauge


Fuel Leak Down Test
1.Depressurize the gas line by opening the gas cap.
2. Tee in a fuel pressure guage between the fuel filter and the injector rail.
3. Replace gas cap.
4.Once installed and tightly sealed, turn the key to the "ON" position [dont start the car]. The gauge should pop up to around 40 psi and hold. If after the pump shuts off [about 5 secs] the gauge starts to fall off rapidly or more then 10 psi in 10secs you have a leak down somewhere in the system.
5.You now need to repeat the process but pinch off the fuel line between the fuel filter and your pressure gauge as soon as it reaches pressure. If it continues to leak down you have now eliminated the fuel pump check valve and your problem lies in the rail or the pressure regulator. If it didnt leak down you have a fuel pump check valve problem.
6. If leak down still occured ,you now need to do the test again ; this time pinch off the return line. If it still leaks down, you need to redo the test and pinch both the lines . If at this point it still leaks down, you have a leaking injector. If when you pinched the return line and it didnt leak down, your pressure regulator is leaking.
Fuel pressure regulator (http://forums.nicoclub.com/zerothread/160216)( this article has the specs for fuel pressure ie 34/43psi
Fuel Injector Leak test (http://forums.nicoclub.com/zerothread/294967)
http://img442.imageshack.us/img442/8333/img01581aw1.th.jpg (http://img442.imageshack.us/my.php?image=img01581aw1.jpg)

You need the fuel injector gauge. Normal gas gauges are much lower pressure.
http://img249.imageshack.us/img249/6171/img01544qw0.th.jpg (http://img249.imageshack.us/my.php?image=img01544qw0.jpg)
http://img249.imageshack.us/img249/1511/img01563sq6.th.jpg (http://img249.imageshack.us/my.php?image=img01563sq6.jpg)

[LA_phantom_240]

Now, correct me if I'm wrong, but a faulty check valve in the fuel pump wouldn't cause my car to lose power like its leaning out or running excessively rich, would it?

Just trying to cover my bases.

[jppierre]

sorry for reviving this thread but i have the same issues, did you find what the problem was? i have the same symptoms, car is hard to start and when it starts it idles shitty and warms up pretty fast, as soon as it warms up it idles fine but if i give it gas it wants to die so i have to ease on the gas pedal to get it to rev up and as soon as i hit boost it leans out big time and after letting go of the gas it backfires like crazy and pops, and it revs up intermittent like cutting off, i checked 3 times for boost leaks by pressurizing the pipes and also my timing is right on, compression is good and leakd own test good as well, i just put the head in this engine and evrything is torque to spec, all coilpacks fire right and tps is good aswell, tried 3 diferent mafs and 2 ecus, im thinking fuel but injectors dont leak, and i have a new 255 fuel pump but its missing the little rubber part that holds the pump down (the car was like that when i got it)