OT - 99 Ranger 4.0 - Fuel Presure Problem

Apr 10, 2004 5 Replies

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Just me... 22 years ago

Having problem with my 99 Ranger 4.0, rough idle, rough starting. Bought it last summer with 105,000 miles on it with unknown service past Problem is sporadic sometimes idle is good and other times it's so rough that the truck dies while backing out the drive (usually it's the worse when the engine is cold). I have replaced MAF, idle control valve, plugs, plug wires and the ignition coil; all with really no effect expect after replacing the MAF, the truck has much more power but idle is sporadic with roughness.

In thinking back about the idle problem and having poor gas mileage, I started thinking more on line of fuel issues; I bought a fuel pressure tester and checked it. To my shock the fuel pressure is 65 lbs at idle, as I understand according to my Chilton's book the pressure should be more like

30 lbs at idle. Would I be correct to replace the fuel pressure regulator? to my understanding the regulator on the 99 is a non-returning regulator so a plugged return line wouldn't be the issue.

Any thoughts on this?

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Jim Warman 22 years ago

The 4.0 (both flavours) has a problem with intake gaskets.... on the OHC motor you might as well change both upper and lower. Symptoms include hard start cold, stalling cold and rough idle. P0171 and P0174 may also be present.

The correct fuel pressure for your Ranger is 56 - 72 psi.

HTH

Jim Warman snipped-for-privacy@telusplanet.net

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Just me... 22 years ago

Thanks for the insight; I really need to find me a real "ford" tech cd... this is not the first time Chilton has mislead me! Is there any place on the web were I can confirm the fuel pressure specs; no offense, I believe you are right as I never heard of fuel pressure like that being over spec by that much as mine is.

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Jim Warman 22 years ago

That spec is off the 1999 Ford service DVD. For your own you can try Helms or look here

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. Doubt me all you want.... I'm a senior tech for one of those dreaded Ford dealers.

The higher fuel pressures mean that the injector tip operates at a higher pressure drop. This allows for a finer spray and better atomization with the benefit that slight pressure fluctations have a less noticeable effect on the spray pattern. The fuel pressure regulator is mounted in the fuel pump module. Since about 2002, most Fords have a fuel pressure transducer mounted on the fuel rail and the PCM supplies pulse width modulated power to the fuel pump.

1998 was the first year for the higher fuel pressure on the 4.0s. FWIW, just about any Explorer owner can vouch for the intake gasket syndrome.

Jim Warman snipped-for-privacy@telusplanet.net

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Just me... 22 years ago

Oh no, I am not doubting you, just kicking myself for putting any faith in my Chilton book!!

And yes I have had the P0171 and P0174 code as you mentioned and the intake gaskets make sense as there seem to be a relationship with the engine being cold or hot (sometimes) with very little relationship to the parts I have replaced and unfortunately it seems to be getting worse.

After checking prices for fuel regulator and fuel pumps, upper/lower gaskets are a much cheaper option short of my time to do it, I am in the middle of trying to get my 65 Mustang coup painted and garage space at home is a premium.

Thank you for your insight!!

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