Well, just spent an hour writing out a detailed description and lost it trying to post it so here is the short version.

99 Blazer (Trailblazer) 4x4 4 door 180,000 kms
Sat for 6 months with a rod knock.
New engine with 1000 kms.
Throwing codes P0171/P0174
Hesitates on start up and wot, I believe whenever the fuel system goes in to open loop.

New parts:
Plugs/wires/cap/rotor - all ngk
Fuel pump - Delphi
FPR
O2 sensors
MAF sensor
Catalitic converter

Key on 56 psi.
Drops to 54 psi.
50 psi after 20 mins.
Idles at 49 psi.
Throttle snap jumps to 56, drops to 46, levels out at 49.
My old fuel pump had higher pressure but the check valve leaked, maybe the new fpr is a faulty one?

Idles smooth at 650 rpm.

Vacuum gauge reads a steady 16 hg at idle, drops to 0 when I snap the throttle. May be a bit low due to the elevation here, 3500 feet.

I've gone over this engine with propane about 10 times, plugged every vacuum line with no changes in vacuum or fuel trim.

STFT will drop to 0 when I snap the throttle, B1 and B2 vary by 3-5%.

STFT- 6-16% @ idle 20% @ 2500 rpm
LTFT- 25% @ idle 15-20% @ 2500 rpm
MAP- 8.8 hg @ idle 7 hg @ 2500 rpm
Spark Advance- 17-19 @ idle 34-35 @ 2500 rpm
IAT- 90 deg F
TPS- 0 @ idle 8.5 @ 2500 rpm
MAF- .6 lbs/min @ idle - 2.4 lbs/min @ 2500
Has hit 19 lbs/min @ wot while driving.
Load- 2.7% @ idle 12% @ 2500 rpm
ECT- 194 deg F

Could someone please take a look at these numbers and tell me what you think? I've spent countless hours reading trying to figure this out. Thanks.

Edit: I have also cleaned the EGR valve, it is working properly. Same with the IAC.

 

Unless I'm mistaken, you should have at least 60 PSI with the key on. If you recently replaced the pump, I'd take a look at the injector and fpr. It sounds like you are having the exact same problem I just had, although my issue was the fuel pump. Try testing the fuel pressure at the filter, see if it's higher and whether it bleeds off. If it's where it needs to be and stays there, it's not the issue.

 

I agree, fuel presure is too low. Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes. There's a fuel system diagnosis thread here on the forum. Find and fix the fuel delivery problem, then replace the NGK parts with AC Delco, should run a TON better.

 

here is the fuel diag link

https://blazerforum.com/forum/tech-articles-diy-29/96-fuel-system-diagnosis-23038/Fuelpressure test