hi my blazer is a 1997. well about a month ago i put a new fuel pump in it due to long hard starts. it fixed that issue. now a month later i have a p0171 and a p0174 code. wich is bank one lean and bank 2 lean. i did go the cheap way and get the pump off ebay so maybe the pump is bad
checked the fuel psi got about 51 while running. shut it off came back like 15 min later it was down to 40ish. a yea and the truck is running rough at idle no miss fire codes and feels like it lacks alot of power...

think maybe i should pull the intake off and see if it is wet i under there like maybe the regulator is leaking? or might it be a cheao pump?

 

Key ON, engine OFF, fuel pump running: fuel pressure must be 60psi to 66psi and must remain above 55psi for a minimum of 10 minutes after the pump shuts off. This thread explains: https://blazerforum.com/forum/showthread.php?t=45941

 

ok thanks... well how od i tell if i should do the pump or regulator? gonna try to do this tomorrow. wanna do it right got the money now so if its the pump iam getting the acdelco.

 

Immediately after the pump pressurizes the system, the pump must be isolated. If pressure does not drop, the pump is leaking. If pressure still drops, the problem is in the plenum, (injector or regulator). Injector balance test will determine if injectors are leaking, if not, it's the regulator.

 

ok thanks... gonna go pull it in and see what i can find.. if it was a injector woulldnt it have a misfire?

 

If an injector is not sealing, it will cause excessive leakdown like you're experiencing, and most likely a misfire and a rich DTC also. If the regulator is leaking externally in the plenum, you MIGHT get a misfire and a rich DTC. Both of your DTC's are indicating a lean condition, so that pretty much blows both of those possibilities out the window. Either the line from the pump to the module, or the check valve in the pump is leaking, that's my bet.

 

srry to be such a pain... but i did replace the pump today. just came in from doing it. it kinda helped but not really. now i get up to about 61psi with koeo. the second i start the truck the psi goes down to 50.... let it sit for about 20min while i put tools away and it didnt leak down any held at 61. is it worth trying the regulator?

 

o and if i rev it quickly it will go up to 61ish than right back to 50.. and almst stall never goes below 50... the almst stalling thing isnt new it did that before with the old pump too.

 

ok well just went down to the shop to check to see if the pressure dropped and sure enough it did. the guage now reads 42psi so within a hour it dropped about 20psi

 

GM does not publish any "engine running" fuel pressure specs for this engine, there are far too many variables involved. Maximum regulated fuel pressure is achieved when there is no manifold vacuum applied to the fuel pressure regulator, (engine off). When the engine is at idle, vacuum is applied to the regulator and the fuel pressure drops, (normal). When you jazz the throttle, manifold vacuum decreases and fuel pressure increases to its maximum, in your case, 61psi.

61psi is just about at the bottom of the spec range. These things perform their best when fuel pressure is 64psi. Some regulators are adjustable, some are not. The ones that are have a tamper resist torx screw on the back of the regulator. Increasing spring pressure on the back side of the diaphragm increases fuel pressure. This image is similar to the regulator on your engine. The adjustment screw is where the vacuum port is in this image, and the vacuum port goes out the side.



Check fuel pressure and leakdown again, without starting the engine. After the pump shuts off, the pressure must remain above 55psi for at least 10 minutes, (longer is better).