My 2003 Suburban (5.3 litre automatic, E85 fuel compatible) has the check engine light on.

The codes my mechanic get are P0171, P0174 and P0300 indicating O2 Sensor's lean, missfire and low fuel pressure. The fuel pump and filterhave been replace as well as the truck been tuned up. The fuel pressure at key turn on is 50 psi, specs require 53-60. Fuel pressure when running is 40-42 psi. The truck has a rough idle in cold weather (below freezing) only. It runs great otherwise. This problem first surfaced in the winter and dissappeared in the summer. It has 130000 km or 80000 miles. We run regular gas, not the E85.

Help!

 

I'm no expert on this but proper fuel pressure has got to mean somthing. Was researching fuel pressure for my 02 Malibu and found that many of the aftermarket pumps just weren't up to providing proper pressures (somthing about pumps having to cover numerous models and such)and that performance suffered as a result.Could a fuel pressure regulator be the gremlin? Don't know but maybe one of the professional techs on the forum might have some ideas. Be patient, they have "lives" other than this forum.

 

Being the vin 'Z' motor, fuel pressure spec is 48-54 KOEO & -3 to 10 psi KOER. Fuel pressure is in spec. You need to check your intake gaskets (runs bad when cold). They will shrink & leak when cold, swell & seal when warm.

 

Thank you jkgray, that is the same answer I got in the Suburban thread where I also posted this question.