Engine/Transmission (1998.5 - 2002) Are these fuel pressures bad?

[CTaylor]

Guys the 99 in my sig has been acting funny so I ordered a fuel pressure gauge from Genos and this is what I found. I tested the pressures at the port closest to the vp44 and at idle the gauge read 8. 5 and it dropped to 6. 5 at 2000rpm where it runs very bad and smokes alot. Are the presures signs of a failed lift pump?

 

[CEdwards]

yes, that pressure is extremely low for idle and for 2000 rpm with no load. It is either suction leak, lift pump, or fuel filter. You will have to eliminate the possibilities or start replacing parts.

 

[Sticks]

Do a pressure check pre filter. If still low, likely you transfer pump is dieing.

10 psi minimum at the VP at all times.

 

[JLandry]

Definitely replace your fuel filter and check the pressure again, but I'm going to respectfully disagree with the other esteemed members of the forum here and say those fuel pressure readings alone are probably not cause of the engine running rough. While less than ideal, 5psi MINIMUM under full load while driving is adequate. The VP44 simply needs positive fuel pressure under all operating conditions for a long and healthy life. Having said that, I start to get nervous whenever I see pressures under 10psi in my own truck because that doesn't leave much room before a dirty fuel filter or weak lift pump can cause the fuel pressure to drop below the 5 psi danger zone.

If after changing the fuel filter the pressure is still close to 5psi under full load during a road test, then I'd definitely explore your options on correcting the problem. It could be caused by a weak lift pump or a fuel system restriction.

As far as running rough and smoking at 2000 rpm, that could be a failing VP44 or a bad injector(s). How many miles on the engine and VP44? Did this condition come on suddenly or gradually? Is the engine low on power?

Regards,

John L.

 

[DavidC]

The port closest to the Vp is post-filter on a 99. The rear port closest to the firewall is pre-filter. Try measuring the rear port as that will be your lift pump pressure. May save you the cost of a filter.



Dave

 

[CTaylor]

Definitely replace your fuel filter and check the pressure again, but I'm going to respectfully disagree with the other esteemed members of the forum here and say those fuel pressure readings alone are probably not cause of the engine running rough. While less than ideal, 5psi MINIMUM under full load while driving is adequate. The VP44 simply needs positive fuel pressure under all operating conditions for a long and healthy life. Having said that, I start to get nervous whenever I see pressures under 10psi in my own truck because that doesn't leave much room before a dirty fuel filter or weak lift pump can cause the fuel pressure to drop below the 5 psi danger zone.



If after changing the fuel filter the pressure is still close to 5psi under full load during a road test, then I'd definitely explore your options on correcting the problem. It could be caused by a weak lift pump or a fuel system restriction.



As far as running rough and smoking at 2000 rpm, that could be a failing VP44 or a bad injector(s). How many miles on the engine and VP44? Did this condition come on suddenly or gradually? Is the engine low on power?



Regards,



John L.

Thanks for the reply and sorry so long to get back but I had to run out of town for work. The fuel filter was replaced before I tested the fuel pressure. The problem actually came on suddenly. I drove the truck for 3 days after I bought it and it ran like a champ. It sat in the driveway after that for a week and then when I went to drive it after that I noticed it lost all its power. The vp44 is a reman unit installed by the previous owner. I havent driven the truck at all since it started this problem, it is now in the garage!