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Old 04-19-2011, 06:50 PM   #1
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How to test the Fuel Pressure Regulator?

My TJ is getting 5-6 PSI when I turn the key to the on position and if I crank it. It won't start up.

I pulled out the tank and the fuel pump works.

Is there a way to test the fuel pressure regulator to see if it's working or not? I hope it's not just a clogged fuel line.

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Old 04-19-2011, 07:12 PM   #2
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The TJ's normal fuel pressure is 49 psi. With only 5-6 psi, I'd probably suspect the fuel pump or a leak more than the fuel pressure regulator.

One thing you can do is to have someone try to pressurize the fuel system by cycling the fuel pump a half-dozen times with the ignition key while you stick your ear next to the gas tank and listen for fuel trickling back into the tank after the last time the pump shuts off. If you hear that, and it's audible if the check valve is leaking, odds are very good the fuel pressure regulator's check valve is leaking which could account for the low pressure.

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Old 04-19-2011, 07:19 PM   #3
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Could it also be a bad fuel injector?
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Old 04-19-2011, 07:21 PM   #4
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could be, mine was (leaking). but because your fuel pressure is so low, its probably a pump/regulator type of problem. (my guess)
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Old 04-19-2011, 07:23 PM   #5
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Could it also be a bad fuel injector?
Get a mechanic's stethoscope and place its tip on each of the fuel injectors after you cycle the fuel pump several times to build as much pressure as possible. If one is leaking, you may be able to hear it. But I still think the #1 most likely suspect is the fuel pump itself.
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Old 04-19-2011, 07:24 PM   #6
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Here is a video of the fuel pump. I connected it to a 12V 10 AMP battery. Is this enough flow?

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Old 04-19-2011, 07:40 PM   #7
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That's not a helpful test because that volume could conceivably drop off to nearly nothing when it is being pumped into a resistance... i.e. the fuel system. Like a small hole in its diaphragm that isn't a problem until it has to pump into resistance when it would only start leaking then. That is like an air compressor that can put out 3 cfm into no resistance but drop down to .5 cfm once it has to pump into resistance.
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Old 04-19-2011, 09:38 PM   #8
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I just attached a tire valve to a hose and checked the pressure by using a tire pump. The fuel pressure regulator holds 40+ PSI and opens up when it goes past that point. After that, I attached a battery to the fuel pump and it holds 40-45 PSI... Injectors? Clogged fuel line?



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Old 04-19-2011, 10:25 PM   #9
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I removed the fuel line from the fuel rail and pumped air into the rail and it easily goes to 40 PSI+. No fuel injector leak. I wonder if it's a clogged fuel line? Is there an external fuel filter on the 1997 Wrangler Sport?
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Old 04-19-2011, 10:30 PM   #10
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I'm going to put everything back. I think the next thing for me to do is to apply 12 volts to the fuel pump to see if I get 40+ PSI reading. If so, then it must be an ECU problem?
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Old 04-19-2011, 11:02 PM   #11
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Ok, so I did one more round of testing and the fuel pressure regulator is hissing out air. It takes 18 seconds to drop down from ~40 PSI to ~20 PSI. Is this normal?
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Old 04-19-2011, 11:12 PM   #12
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Old 04-20-2011, 08:59 AM   #13
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Quote:
Originally Posted by Rise View Post
Is there an external fuel filter on the 1997 Wrangler Sport?
No, the only fuel filter is inside the fuel pressure regulator.

Quote:
Originally Posted by Rise View Post
It takes 18 seconds to drop down from ~40 PSI to ~20 PSI. Is this normal?
No, it should hold pressure indefinitely.
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Old 04-20-2011, 09:30 AM   #14
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If your fuel pressure is not 49 psi +/- 2 psi at idle, then your pump is not working to spec and should replaced. Also it sounds like yours is leaking down much too fast through the check valve. Mine would hold max pressure for well over a minute once I replaced it (actually longer but I pulled the gauge after that). Before I changed it, it would drop very slowly over the course of 30 seconds or so.

-Wes
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Old 04-23-2011, 03:54 PM   #15
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I replaced the fuel pump with a Walbro 255 and a new FPR. It works outside of the car, but after I mounted the fuel tank back on, it's only getting < 5 PSI. Jeep still doesn't start up.

I pulled out a 12V battery and attached it directly to the fuel pump and the pressure at the fuel rail reads 50+ PSI.

I crank the engine and it starts but the pressure drops fast down to 5 PSI or so and the engine shuts off.

I'm guessing it's a wiring issue? Grounding issue? or a bad ECU?
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Old 04-23-2011, 04:42 PM   #16
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This is really a mystery. Since we're now kinda grasping at straws, try swapping the fuel pump relay with a different relay (but not the ASD releay) inside the Power Distribution Center. If that doesn't do anything, try swapping the ASD relay with a different relay, but not the fuel pump's relay. Many of the relays inside there are the same so you can swap them around as a way to test them.
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Old 04-23-2011, 06:21 PM   #17
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I finally got it to work. For some reason, the power at the fuel pump is only reading 4.0 Volts. I temporary ran a line from the Fuel Pump relay to the fuel pump and it works. What would cause the volts to drop to 4.0 instead of 12?

And where is the fuel pump fuse on the 1997 JEep wrangler? I looked everywhere (relay box under the hood) and behind the glove compartment, but I don't see the fuel pump fuse. I checked all of the fuses too and they are all fine.
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Old 04-23-2011, 06:35 PM   #18
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Quote:
Originally Posted by Rise View Post
I finally got it to work. For some reason, the power at the fuel pump is only reading 4.0 Volts. I temporary ran a line from the Fuel Pump relay to the fuel pump and it works. What would cause the volts to drop to 4.0 instead of 12?
Cracked wire insulation, or corroded connectors? With the ignition off, try running an Ohmmeter between the back of the connector and a clean spot on the frame. If it reads less than 10k Ohms you may have a partial short somewhere. Maybe trace the pump power wires back and see if the insulation has been rubbing/pinched somewhere.
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Old 07-21-2011, 09:41 AM   #19
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Quote:
Originally Posted by Rise View Post
My TJ is getting 5-6 PSI when I turn the key to the on position and if I crank it. It won't start up.<br />
<br />
I pulled out the tank and the fuel pump works.<br />
<br />
Is there a way to test the fuel pressure regulator to see if it's working or not? I hope it's not just a clogged fuel line.
<br />
<br />
Hi everybody. I am a first time poster. I have a 97 Wrangler which hasn't been driven in a few years. Before trying to start it, one of the things I did was take out the gas tank, partly because I was curious and it also made it easier to replace the old fuel. Now that I am at the point where I am trying to start it, I am finding that I am not getting fuel pressure.

How do you test the fuel pump to see if it is working properly? With the key in the ignition, I am getting 5 volts / 45 ohms at the plug leading to the fuel tank. In the diagram below, node 1 was the only one getting power:
.....______
___|........|___
|...1.........2....|
|...................|
|__3_____4__|

Thanks in advance!
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Old 07-21-2011, 03:37 PM   #20
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I pulled this from the FSM and plan to run the test soon. I'll post the results.

DIAGNOSIS AND TESTING - FUEL PRESSURE
LEAK DOWN TEST
Use this test in conjunction with the Fuel Pump
Pressure Test and Fuel Pump Capacity Test.
Check Valve Operation: The electric fuel pump
outlet contains a one-way check valve to prevent fuel
flow back into the tank and to maintain fuel supply
line pressure (engine warm) when pump is not operational.
It is also used to keep the fuel supply line
full of gasoline when pump is not operational. After
the vehicle has cooled down, fuel pressure may drop
to 0 psi (cold fluid contracts), but liquid gasoline will
remain in fuel supply line between the check valve
and fuel injectors. Fuel pressure that has
dropped to 0 psi on a cooled down vehicle
(engine off) is a normal condition. When the electric
fuel pump is activated, fuel pressure should
immediately (1–2 seconds) rise to specification.
Abnormally long periods of cranking to restart a
hot engine that has been shut down for a short
period of time may be caused by:
Fuel pressure bleeding past a fuel injector(s).
Fuel pressure bleeding past the check valve in
the fuel pump module.
(1) Disconnect the fuel inlet line at fuel rail. Refer
to Fuel Tubes/Lines/Hoses and Clamps for procedures.
On some engines, air cleaner housing removal
may be necessary before fuel line disconnection.
(2) Obtain correct Fuel Line Pressure Test Adapter
Tool Hose. Tool number 6539 is used for 5/16” fuel
lines and tool number 6631 is used for 3/8” fuel lines.
(3) Connect correct Fuel Line Pressure Test
Adapter Tool Hose between disconnected fuel line
and fuel rail (Fig. 1).
(4) Connect the 0-414 kPa (0-60 psi) fuel pressure
test gauge (from Gauge Set 5069) to the test port on
the appropriate Adaptor Tool. The DRBt III Scan
Tool along with the PEP module, the 500 psi
pressure transducer, and the transducer-to-test
port adapter may also be used in place of the
fuel pressure gauge.
The fittings on both tools must be in good
condition and free from any small leaks before
performing the proceeding test.
(5) Start engine and bring to normal operating
temperature.
(6) Observe test gauge. Normal operating pressure
should be 339 kPa +/–34 kPa (49.2 psi +/–5 psi).
(7) Shut engine off.
(8) Pressure should not fall below 30 psi for five
minutes.
(9) If pressure falls below 30 psi, it must be determined
if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking.
(10) Again, start engine and bring to normal operating
temperature.
(11) Shut engine off.
(12) Testing for fuel injector or fuel rail leakage:
Clamp off the rubber hose portion of Adaptor
Tool between the fuel rail and the test port “T” on
Adapter Tool. If pressure now holds at or above 30
psi, a fuel injector or the fuel rail is leaking.
(13) Testing for fuel pump check valve, filter/
regulator check valve or fuel tube/line leakage:
Clamp off the rubber hose portion of Adaptor Tool
between the vehicle fuel line and test port “T” on
Adapter Tool. If pressure now holds at or above 30
psi, a leak may be found at a fuel tube/line. If no
leaks are found at fuel tubes or lines, one of the
check valves in either the electric fuel pump or filter/
regulator may be leaking.
Note: A quick loss of pressure usually indicates a
defective check valve in the filter/regulator. A slow
loss of pressure usually indicates a defective check
valve in the electric fuel pump.
The electric fuel pump is not serviced separately.
Replace the fuel pump module assembly. The filter/
regulator may be replaced separately on certain
applications. Refer to Fuel Filter/Fuel Pressure Regulator
Removal/Installation for additional information

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