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Old 07-27-2014, 07:27 AM   #1
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Default Fuel Pressure Regulators

Are they interchangeable? 86-89, 90-94 and 95-97 are all different in the direction the fuel line and vacuum line face. Do they all work at 37psi? Any input is greatly appreciated!
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Old 07-27-2014, 07:57 AM   #2
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I looked in the Haynes Manual.....

so I'm assuming that each regulator has a different set pressure.
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Old 07-27-2014, 01:22 PM   #3
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That's what it looks like
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Old 07-27-2014, 03:00 PM   #4
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from ALLData Pro................



  1. (step 6) Install a high-pressure fuel gauge (0 to 60 psi) between the hose and throttle chamber.
  2. (step 7) Start the engine and check for leakage at the fittings.
  3. (step 8) Allow the engine to idle and observe the gauge reading.
    1. If fuel pressure is 36.3 psi (250.1 kPa, 2.55 kg/cm2), fuel pressure is O.K.. END TEST.
    2. If fuel pressure is below 36.3 psi (250.1 kPa, 2.55 kg/cm2), proceed to step 9.
    3. If fuel pressure is above 36.3 psi (250.1 kPa, 2.55 kg/cm2), proceed to step 15.
  1. (step 9) Disconnect the fuel pressure regulator vacuum hose and check for vacuum at the fuel pressure regulator hose.
    1. If vacuum does exist, proceed to step 10.
    2. If vacuum does not exist, inspect the throttle chamber for restriction and clean and replace as needed.
  1. (step 10) Observe the gauge readings.
    1. If fuel pressure does not raise after removing vacuum hose, replace the fuel pressure regulator and re-test.
    2. If the fuel pressure does raise, inspect the fuel filter for restriction, if O.K. proceed to 11.
  1. (step 11) Remove the fuel cap and retest.
    1. If O.K., replace the fuel cap and re-test.
    2. If no change occurs, proceed to step 12.
  1. (step 12) Remove the fuel pump and inspect the pick-up screen for restriction.
    1. If O.K. proceed to step 13.
    2. If not O.K., clean the screen and re-test.
  1. (step 13) Inspect the fuel delivery lines for restrictions (kinks, bends or collapsed hoses).
    1. If O.K. proceed to step 14.
    2. If not O.K., repair or replace as needed and re-test.
  1. (step 14) Replace the fuel pump and re-test.
  2. (step 15) Disconnect the fuel pressure regulator vacuum hose and check for vacuum at the fuel pressure regulator hose.
    1. If vacuum does exist, proceed to step 16.
    2. If vacuum does not exist, inspect the throttle chamber for restriction and clean and replace as needed.
  1. (step 16) Observe gauge readings.
    1. If fuel pressure does not raise after removing vacuum hose, replace the fuel pressure regulator and re-test.
    2. If the fuel pressure does raise, proceed to step 17.
  1. (step 17) Inspect the fuel return lines for restrictions (kinks, bends or collapsed hoses).
    1. If O.K. proceed to step 18.
    2. If not O.K., repair or replace as needed and re-test.
  1. (step 18) Replace the fuel pump and re-test.
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Old 07-27-2014, 03:04 PM   #5
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for some reason when i pasted the testing steps, it omitted the proper step numbers and showed them all as 1. i fixed that with the proper step number in parenthesis.
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Old 07-27-2014, 04:05 PM   #6
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Quote:
Originally Posted by cadillacdude1975 View Post
for some reason when i pasted the testing steps, it omitted the proper step numbers and showed them all as 1. i fixed that with the proper step number in parenthesis.
Thanks, I'm just trying to see if my regulator is working properly. I was thinking of swapping it out with one from another vehicle. Maybe that's the issue with my starting problems and black smoke at start up. Last I checked like 2 months ago the fuel pressure was good. My question is, is the pressure supposed to stay at 36 psi even after turning off the engine? Or drop back to 0?
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Old 07-27-2014, 04:15 PM   #7
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It should remain under pressure for a little while. I'm not sure for how long, but it should be close to the desired pressure for several hours at a minimum I would think. Dig through the FSM and see if you can find any mention of it.
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Old 07-27-2014, 10:20 PM   #8
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Alright, I just comfirmed that the fuel pressure regulator is bad. I was doing some research on YouTube about fuel pressure regulators. The diaphragm is ruptured and is sucking fuel through it and dumping it in the throttle body. Here's a pic if the open port from where the regulator gets its vacuum from. That's where fuel was coming out of.
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Old 08-02-2014, 05:56 AM   #9
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Hahahaha yeah I was just going to say that fpr is vaccum controlled by a hose connected to manifold vacuum, so when intake manifold vacuum is high and pressure is low, throttle plate is closed fuel pressure is low, as manifold pressure increases as the throttle plate opens fuel pressure increases proportionally by the fpr.

So when the diaphragm inside is ruptured, it draws unmetered fuel into the intake manifold by vacuum and the air fuel mixture is way too Rich causing incomplete combustion and hence the black exhaust smoke is proof of that.

Easiest way to test the fpr is to disconnect the vaccum hose running to it with the engine running and a fuel pressure gauge connected to the port on the fuel rail. Fuel pressure doesn't increase then the regulator is bad and needs replacing.

Also keep in mind that leaky fuel injectors that don't close all the way make the air fuel mixture too rich and cause black exhaust smoke. 240sx kids always have that problem and its funny to see them scratch their heads
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Old 08-02-2014, 06:01 AM   #10
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Also the fpr blocks off the fuel return line to the fuel tank when the engine is shut off that way residual pressure remains inside the fuel rail making engine restarting easier as the fuel pump doesnt have to build as much pressure right away. If you have a long crank at cold start up either the fpr is bad or the pump is going bad as it cannot build enough pressure fast enough and provide adequate fuel volume to the fuel rail and hence the injectors
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