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Fuel Pressure Reg


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#1 bigdaddy78

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Posted 26 February 2012 - 10:35 AM

Has anyone else had the regulator go bad? I noticed at higher rpm range it would not pull passed 130. I put the gauge on it and noticed pressure dropping off at higher rpms. removed the vacuum line and cleaned it out with brake cleaner. worked great for a while. now its acting up again. Has anyone else had their reg go out?

#2 ionbeam

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Posted 26 February 2012 - 11:28 AM

...I put the gauge on it...Has anyone else had their reg go out?

Gen I fun only, Gen II does not have the same fuel pressure management.

There have been no fuel pressure regulator failures that I know of, but it really doesn't matter if others have had a pressure regulator problem or not.

The fuel pump is electrical and independent of engine speed, it should always pump at a steady pressure using the fuel pressure regulator to adjust pressure.

If you have a way to hook your fuel pressure gauge to the fuel rail you have the hard part of the test already done. Hook the fuel pressure gauge to the fuel injector rail. Take the vacuum hose off the Fuel Pressure Regulator and plug it, then hook a mity vac to the FPR. Start the engine. With no vacuum on the FPR you should read 36 psi if it is working correctly. Now slowly increase vacuum while observing the fuel pressure to decrease in proportion to increasing vacuum. DO NOT EXCEED 1mm Hg (0.039" Hg). That's it. If your fuel rail makes 36 psi it is working correctly.

Engines have the highest vacuum at idle and lowest vacuum at full throttle/full load. When you first start the FPR test with no vacuum you are simulating full throttle and full load. It is at this point where you are seeing the fuel pressure from the pump and the operation of the FPR together. If you see 36 psi on the fuel rail you need to look elsewhere for your lack of top end power.

How many miles on your '03? Did it ever have a 'ticker' repair? This is one time where it is important to ask about the condition of the air filter, 'cause you need maximum air flow to achieve maximum engine power. If you have the means or access to the equipment, now is the time to do a leak-down test.
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#3 3dogs

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Posted 27 February 2012 - 04:54 AM

If your fuel rail makes 36 psi it is working correctly.


The 36 psi is only half the story. Even if fuel pressure is at 36 psi, the volume of fuel delivered from the pump may not be enough to provide full engine power. I worked for Snap On's tech line and when a vehicle had a symptom of "lacks power at full throttle" both fuel pressure and volume were checked. A pump that makes full pressure, but only produces a trickle of fuel, either is not getting enough current (voltage drop issue), is tired/worn out or the fuel filter is starting to plug up. Since genI doesn't have fuel filter it could be the pump (and not the regulator). Easy to check--get the pump to run by jumping the F/P relay, connect a fuel hose to the pump and put the other end into a container. The pump should fill a pint container in less that 15 seconds (or produce a fairly high volume of fuel out of the hose).

#4 ionbeam

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Posted 27 February 2012 - 05:15 AM


If your fuel rail makes 36 psi it is working correctly.

The 36 psi is only half the story. Even if fuel pressure is at 36 psi, the volume of fuel delivered from the pump may not be enough to provide full engine power...

Given the type of fuel system that the FJR has I believe that it is a good bet that if the pressure is good the pumped volume will be good. I didn't mention fuel flow because it is highly unlikely that the flow @ 36 PSI would be limited in our return type FI system.

You are welcome to light a cigarette and pump fuel into a Styrofoam cup for 15 seconds and let us know what the fuel volume should be. :dribble: ;) :lol: On second thought, maybe not :)
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#5 RadioHowie

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Posted 28 February 2012 - 01:51 PM


If your fuel rail makes 36 psi it is working correctly.


The 36 psi is only half the story. Even if fuel pressure is at 36 psi, the volume of fuel delivered from the pump may not be enough to provide full engine power. I worked for Snap On's tech line and when a vehicle had a symptom of "lacks power at full throttle" both fuel pressure and volume were checked. A pump that makes full pressure, but only produces a trickle of fuel, either is not getting enough current (voltage drop issue), is tired/worn out or the fuel filter is starting to plug up. Since genI doesn't have fuel filter it could be the pump (and not the regulator). Easy to check--get the pump to run by jumping the F/P relay, connect a fuel hose to the pump and put the other end into a container. The pump should fill a pint container in less that 15 seconds (or produce a fairly high volume of fuel out of the hose).


3dogs, my FJR experienced exactly the opposite of your description of pressure versus flow. When I went through my failing-fuel-pump issue, my pump could fill up a quart mayonnaise jar in about 10 seconds, but the pressure was too low for the engine to run over 4000rpm. Ran great up to 4k, but then starved out like it was outta gas.

Fuel flowed like a fire-hose, but you could stop the flow with a slight pinch of the gas line...no pressure to keep the flow going.

Here's what was the problem with my pump:

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#6 bigdaddy78

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Posted 28 February 2012 - 07:21 PM

Well, I ordered a regulator, so ill try it out and let. You know.

#7 3dogs

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Posted 29 February 2012 - 04:28 AM



If your fuel rail makes 36 psi it is working correctly.

The 36 psi is only half the story. Even if fuel pressure is at 36 psi, the volume of fuel delivered from the pump may not be enough to provide full engine power...

Given the type of fuel system that the FJR has I believe that it is a good bet that if the pressure is good the pumped volume will be good. I didn't mention fuel flow because it is highly unlikely that the flow @ 36 PSI would be limited in our return type FI system.

You are welcome to light a cigarette and pump fuel into a Styrofoam cup for 15 seconds and let us know what the fuel volume should be. :dribble: ;) :lol: On second thought, maybe not :)

36 psi of fuel pressure without enough volume will cause a lack of power at full throttle. I have worked on 100ís of cars/trucks that had a bad fuel pump that could produce good pressure. The engine would run good at part throttle but not at full. I used a digital lab scope to look at the wave form produced by the fuel pumpís armature. A bad pump could be diagnosed before it actually want bad, thus warning the customer that it was time for a new pump.

It's interesting to note that Snap-On and MAC Tools sells a fuel pressure gauge that has a dedicated extra hose and a trigger valve that allows a pump volume test. I guess only an idiot would use a Styrofoam cup for the fuel volume test and smoke at the same time. Maybe pump volume testing is an activity you should leave to a professional technician.

#8 bigdaddy78

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Posted 15 March 2012 - 06:31 AM

I just put the gauge on it and ran the engine under load at high rpm to test the pressure and volume. if you dont have volume you wont have pressure either at high rpm. anyways I replaced the reg and it runs awesome now.

#9 Fred W

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Posted 15 March 2012 - 09:25 AM

I just put the gauge on it and ran the engine under load at high rpm to test the pressure and volume. if you dont have volume you wont have pressure either at high rpm. anyways I replaced the reg and it runs awesome now.


Well, what the hell good is that kind of feedback? Cause, effect, etc.:rolleyes:

We haven't finished discussin' all of the dad-gummed theory yet. ;)


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