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Fuel Flow Problem


rangerpilot

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A few months ago I swapped out the fuel pump as well as the fuel filter due to a no start situation and a verified no power to the fuel pump.

Ever since this time, when I get below a 1/4 of a tank I have problems with idle when coming to a stop. Sometimes, it will die and other times drop to 300-400 RPMs and finally return back to normal idle.

If I go much longer past 1/4 tank (no fuel light at this point), there are several occasions in which coming off the line at a stop light I will attempt to accelerate normally and the truck will lunge me forward as if something grabbed it by the trailer hitch and tried to stop me. It will jerk and lunge a couple times and then decide to continue forward with no problems ... until I come to a stop again.

It is almost as if it is starving for fuel but it doesn't sputter ... it is a violent event (al be it embarrassing).

Any thoughts?

1999 Ranger 4.0
5 speed manual
4x4
250,000+ miles
 


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RonD

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Not sure about the 1/4 tank thing, did you replace the whole fuel pump assembly, and was it a Ford pump?
May have to get a fuel pressure tester and test it with 1/2 tank, then siphon out some gas and test with under a 1/4 tank, could just be a weak pump.
Fuel pressure should stay between 55-70psi on a '99

If it is not fuel pressure related then I would clean the IAC(idle air control) valve, could be getting sticky and computer is having a hard time stabilizing it.
 

rangerpilot

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Oh yeah...I replaced the IAC, cleaned the throttle body, and MAF (yes, the correct solution) as soon as it started with no luck.

It was a fuel pump from AutoZone. Not sure of the warranty...need to check but finding time to pull it and take it back and then order one from Ford is going to be tough with my schedule right now....although this is probably the best option.
 
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rangerpilot

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Hey Ron ... Just looking through some old posts. Never did figure out this problem.

I do have some conflicting information. Some places say that the 4.0 OHV engine should be 35-40 psi fuel pressure and others (Haynes) say every engine (98-2000) except the 3.0 should have 56-72psi.

At first I read the higher numbers I thought this may be the answer to both the problems below 1/4 tank and now also the problem I have with it running too lean as mentioned in my new thread entitled "Lean Condition - did I cover all bases" (labeled for cross reference purposes).

I am really struggling with the Haynes manual after this as well as the information regarding the fuel pressure regulator ... Haynes says this is located in the tank but I clearly see one with a vacuum line attached to the fuel rail.

Makes me really appreciate online resources like this and causes me to further question all professional publications that are not published by Ford.

Any thoughts on maybe these issues being co related?


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RonD

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Ford switch to a "Returnless" fuel system in the late 1990's, exact year is model and engine specific.

The previous "Return" style had 2 fuel lines at the engine with return line connected to a Fuel Pressure Regulator on the intake manifold.
These were spec'ed for 35-42psi

"Returnless" just has the 1 fuel line at the engine, Fuel pressure regulator is in the fuel tank, these are spec'ed at 65-72psi.

So you just need to look at the engine fuel lines, coming from drivers side of engine compartment, if you see 1 braided fuel line then it's 70psi, if you see 2 then 40psi

The Returnless system does have a Wave Damper at the end of the fuel rail, it has a vacuum line connected, with fuel pressure at 70psi the opening and closing of injectors will create pressure waves in the rail, if these reflect off the end of the rail they could double up and cause problems with lower pressure wave passing just when an injector is opening.
The Damper is just a diaphragm that absorbs a wave so it doesn't reflect.
The vacuum line is just for safety, if diaphragm should leak, fuel could drip down to exhaust or ??, vacuum line would prevent that

Return style caused the fuel to be heated up just a bit from all the traveling thru the fuel lines and warmer engine compartment, so to reduce extra vapors and possibly to increase fuel economy the Returnless system was used
 
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rangerpilot

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I have a return-less system so my fuel pressure is low (solid 40psi both off, idle and high RPMs)

Pump is less than two years old but appears either the regulator is bad or the damper is failing.

Any way to test the damper before I remove the bed and go with the regulator assembly as the problem?

I see both fuel pump/regulator/sending unit assembly and the damper are special order parts.
 

RonD

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Just pull off the damper vacuum hose, if there is fuel in the hose replace damper, but it rarely fails and your symptom would be Rich codes not Lean codes because extra fuel would be coming into intake, via the vacuum hose.
If pressure is stable at 40psi with engine off and doesn't continue to drop then it isn't the damper, or the fuel pressure regulator(check valve) in the tank, it is the pump itself.

Non-MotorCraft fuel pumps can last less than a year or just over a year, I still have original in my 1994, so at 21 years old now, knock on wood.
There are some brands to avoid out right and some that seem to do a better job lasting.
Do a search at TRS(here) to see what members recommend

And yes the 40psi on a Returnless system would account for Lean codes on both banks.
 
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rangerpilot

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Pump Assembly (Regulator, Sending Unit, Pump) all replaced. Both the 1/4 tank problem and the emissions problem (lean condition from another post) are cleared up.

The fuel gauge is still different but it is a different model.

The assembly was a Spectrum Premium Part from AutoZone (special order).

Finally glad to have this solved.
 

RonD

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Good work :icon_thumby:

Thanks for following up and posting the fix
 


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