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I have a 09 Chevy Silverado LT crew cab 5.3 flex fuel with 190xxx . This is a long post the third paragraph is what I need help with for the second paragraph just tells you the story oh I got to the point where I'm at now some info and thoughts on the fuel system. Any info will help me at this point I am so stomped on this lean and misfire code. I have been looking for about 3 months on what the fuel pressure should be on the 5.3 Flex fuels. A long time ago I did hear one time that's a 07 and up 5.3 olny needs 40-45psi. I dont believe its ture. I have talked to a lot of people and nobody could really give me a direct answer. Google suck these days and it's hard to get correct info from there. I completely forgot about this page till today. I havent been searching long today and I have seen a lot saying 50-55psi. that's a PSI that nobody mentioned. Okay so here's some information about the pos I thought I was getting a good deal on after test driving it. I wouldn't even a paid a quarter of what I did if I just drove it couple more miles.

I'm also getting a throttle body sensor code with the p0300 and the p0174 I can't remember the tbs code off of the top of my head(throttle body and sensor are new). I have been trying to figure this out for a long time. When it first started happening there are codes popping up for sensors but one at a time. Almost everyday different cold with pop up. You can order truck with a lot of miles who knows it so sensor forever changed I really had no problem changing out the sensors why not are you run better. I have not yet changed out the PCV valve cover or the engine coolant temperature sensor yet. There was a crack in the OEM air filter tube goin in the intake so i decided to put cool air intake on. Put new spark plugs and wires in. Took out fuel injectors cleaned and tested all good. All coil packs tested all good. I started checking for vacuum leaks all hoses are fine. Couldn't find any vacuum leaks around the motor. I did find the bolts up underneath the intake manifold. So I took the manifold off to torque down the bolts.i change the gasket on the intake manifold and valve covers while I was at it. I added some better grounds at firewall to motor and frame.after all the stuff i did there was no big change. All the same code would still show up. There was about 15 different codes that were always showing up sometimes it was just one sometimes it was almost all of them there were a couple of codes that only showed up one time. But the truck was never affected by the codes like i know some of the code would have. And on top of all of this **** service traction control service abs service stability track or something like that the reduced engine power happened I will always be on my way it never happened more then 3 time in row. It only happen at night after it rained at some point in that day under 60 degrees. The best thing I can find on that was to clean the throttle body or change the throttle body sensor. Happens if their time and happened to me this when I changed throttle body but it didnt help any. Well in the middle of June about 10 in the morning it happened again this time daytime hot and dry. And that time I didn't just get to go on my way cuz it never stop doing it. So the code that was popping up for it was for a 5v open circuit. That circuit blond do all of the sensors that control the fuel air flow I was already suspecting wiring issues way before I found out it was an open circuit issue great now it's time to chase down a damaged. Well the best place to start looking for a damaged wire then where you can see the wires. Well if I nothing you go farther time of day going to that wire harness if you don't find it keep going I ended up having the whole wiring harness out now its a mess after very carefully for a very long time over and over and what did I find NOTHING. so after that I did a voltage test on it every wiring connector the engine bay all good. its time for a new pcm. So after a new PCM and a crankshaft relearn truck driving like new. I'm on my way home from work later that night what do I feel misfire I pull out my scanner and look at it random misfire. too lean and tbs code. Now that I'm moving on from the electrical system it's time for the fuel system


this is where I need all the help I can get. What took me so long to come to the fuel system was a long time ago I heard 07 and up 5.3l only needs fuel pressure of 40-45psi and my truck at cold start 45psi then a minute Issa it drops and stay at 43psi at idle and open throttle. So I always thought I had a good fuel pressure. And now I believe it is way too low and definitely cause it the p0174. The way that I'm coming up with 43psi being low is I also have a evap leak. The only code that I have seen for the evap leak was the PO455 (large leak) so looking into that the purge valve and vent valve are good. I have checked everything out and everything look fine no leaks no gas smell. There's only one thing left to check and that would be fuel pressure regulator and I'm guessing that could also make low psi. Now I also know that the fuel pump can have a lot higher PSI.what i did was i unhooked the engine coolant temperature sensor and now the pmc is reading out temperature -45. like car people know the colder the car the higher the fuel pressure.now im getting a fuel pressure of 58-60psi. And let me tell you my truck is really loving that higher fuel pressure. There is no more misfiring. And when I seen the fuel pressure at 58 60 I think that may be a little too high so I was thinking it needed to be somewhere around 50 psi. I have been trying to figure out the fuel pressure for this truck a couple weeks now answers of low40s high 50s I never got 50 to 55 today was the first time. I'm still wondering if that is the correct pressure. This is the first time i have seen low fuel pressure and knowing the fuel pump can still get a very high one. Okay I have noticed this today and I do not think that it's right I went to the gas station the thermostat on hooked and I'm watching them for pressure on I scanner 5960 PSI when i turned my truck off it was at 62psi but when i came out it was at 80psi it was like my truck was flooded trying to start it. Even rhe low pressure went up 20psi . I know that it will go up a some but 20psi is crazy to me. I feel as when I'm writing this I am starting to figure out the answers to my questions. One thing that I know for sure now is it a fuel system causing all my problems that have been driving me insane.
 
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