More and more I suspect the fuel pressure regulator as the problem. Don't want to keep throwing $50 regulators at it 'till one works BUT at Rock Auto I saw one that had a Torque head in the middle which leads me to believe some are adjustable. The one from the 6.0 that I borrowed had a screw in the middle and I was able to move it but it would not fit my rail due to a different shape on it's backside (inside the housing). On older TPI systems we drilled a hole in the regulator housing, brazed a quarter 20 nut on, dropped a quarter on top of the diaphragm and upped the pressure with a bolt adding pressure to the quarter. This way a 305 TPI would run right on a 350!

 

If you will look on rockauto standard motor products pr217 regulator is what fits your engine if you click on more info you will see operating pressure is 50lb. That is what your engine will run perfect on. My 1953 3100 with 2003 5.3 wifes 2004 Tahoe my 99 Silverado all run the same regulator and all run on 50lbs pressure.

 

Hit your head against the wall long enough and the problem will get solved either by correction or going stupid and don't care anymore. I took the regulator off a friends '07 5.3 (engine/trans waiting for next project) and it produces 60 pounds. Long term fuel trims hover at 0 and no lean codes. I'm happy, the engine is happy but friend is not...got a hole in his fuel rail.

 

your instincts here were spot - on. congrats!

Doug

 

Not2Old pointed out that some of the parts stores list the operating pressure as 50 PSI which is true. My '05 Silverado has a pressure of 58 lbs and is also a 5.3 engine. Fuel trips say the fuel system/engine is happy at 58 lbs and not happy at 50 lbs. Now I'm happy/confused! The ECU has an '05 tune but everything I have read says the operating pressure for LSx engines (4.8, 5.3, 5.7, 6.0,6.2) is 58 lbs. Why sell 50 lb regulators if the design pressure is 58? Tune should not make a difference because the O2 sensor ('03 Trailblazer) is reporting a lean condition at 50 lbs. Can somebody 'splain this to me? Have I opened a can of worms?

 

Now I have a ghost on my hands. After golf today checked everything again before returning the borrowed regulator. Now the pressure reads 50 lbs! LTRT1 reads 12.5% and LTFT2 at 16.4%. Put my regulator back in and pressure is at 48 lbs both trims are at 11.7%. What is going on? As mentioned by Not2Old it seems to run just as well at 50 as it did when the pressure was at 60. Could smell fuel at the higher pressure but it was not in closed loop yet. If the trims stay at 11% I'll be happy with that. By next week I'll be able to road test to see where things settle. https://ls1tech.com/forums/images/sm...r_banghead.gif