Greetings All,
I am working my way through the many items that can cause P0171 & P0174 codes. Replacing a leaking IAC valve made some improvement yesterday. There may still be a vacuum leak although vacuum readings at the plenum are high (21"Hg) and steady. I will continue looking for leaks, but my questions today are about the fuel system.

My fuel pressure readings are 67psi at idle, and do not change when I remove the vacuum line. The line has the same 21" of vacuum as the plenum. Before I run out to buy a regulator I need to learn more about the fuel system to make sure it's not a blockage somewhere. I have changed the fuel filter. Can a failing pump put out max pressure while not delivering enough fuel? There is only one braided hose connected to the fuel regulator, and Haynes calls it the fuel return. I am looking for a supply to the fuel rail? Haynes mentions a fuel charging manifold, but does not show it or tell you where it is, and I need to know how that functions and whether there could be a blockage there? Can I measure the volume of fuel delivery to know if I have to change the pump.

I realize I need a factory manual, but any help with my questions would be greatly appreciated. I can only check the form a couple of times a day so may not respond immediately.
Thank You,
fastvee

 

The two codes are lean on both banks. I would look for a vacuum leak in the system, i.e. pcv hoses or valve, snorkle tube loose between air box and throttle body, intake gasket leaking (seen lots of these), or dirty mass air meter (cleaning the hot wire will ususally fix this) or just a bad meter. Doubt you have fuel delivery problems. Just my opinion

 

Oh, and to answer your question about the fuel charge rail, that is the fuel manifold that your injectors are hooked to. Blockage here would cause stalling and no performance at all.

 

Thanks oldtimer35. I did find two more vacuum leaks last night. One was at the throttle body gasket behind the plastic shield, and the other was a hole worn through the hose from TB to evap valve. I temporarily fixed those items until I can order parts and the short term fuel trims responded. P0171 returned this morning and it looks like I'll be looking for more vacuum leaks. I am starting to suspect that I didn't get the lower intake manifold sealed well enough. I hope that I didn't distort it. Chiltons said 18 ft lb, but my new Haynes shows 12 ft lb.
I am not so worried about the fuel pressure since the fuel trims returned to normal, but I may still have a problem there. My next step was to see if the regulator holds vacuum, but the check valve in my hand pump has failed.
Thanks,
fastvee