New to the forum, trying to figure out my issue. The Blazer will fire right up and rev fine, as soon as you put it into gear and give it throttle, it wants to stall out. It will sputter down the road and does this a few times, by the time I get 100' down the road and stop, it wont do it again until the next start up. Seems worse when it is not at operating temps but has done it at normal temp as well but only after restarting the engine. It has 126k on the clock.

I have had the spider injectors replaced and some vacuum lines repaired at a shop. I have replaced the MAF, EGR, PCV, O2 sensor # 3, a few more vacuum lines, fuel filter,air filter, fuel pump, plugs, wires, rotor, cap and gas cap. Can't get the fuel pressure over 50psi. and the vacuum is around 20.

I do have a P0171 & P0174 code that I assume is related? Any help would be appreciated. This is my sons first car and I'm having trouble getting it on the road.

 

What year? What actually is the fuel pressure?
A good start is to get the OBD scanner and check the fuel trims on both banks. Definitely cheaper and faster than replacing everything around.
EDIT: Oh, the codes are for lean mixture, but I'd get a scanner to get some live data.

 

What Mike said.

George

 

 

We need four numbers for fuel trim (including the sign/polarity). Short tern and long term for both banks.

George

 

 

 

You do indeed have a significant problem. The vehicle monitors the exhaust with the O2 sensors and keeps adjusting the fuel delivery to match the airflow and develop the most efficient air/fuel mixture and hence the lowest emissions. The only exception to this is initial open loop operation when the engine is cold, full throttle and limp home mode. Then the computer takes all the sensor inputs (ECT, MAF, etc), looks in a hard coded table and compares the current fuel delivery with the theoretical fuel delivery based on the sensor readings and gives you the deviation between the actual fuel delivery as determined by the exhaust/O2 sensors and the theoretical based on the look up table - in the form of fuel trims. The long term trim for a given bank is the long term average departure from theoretical and the short term trim is the instantaneous deviation from theoretical. The trim or deviation from theoretical is always the addition of LT and ST trims for a given bank, being mindful or sign. Net fuel trims should be single digit numbers, >25 triggers a code and yours are defcon 5. Positives net numbers mean that the computer is adding fuel to compensate for a lean condition and net negative numbers mean that the computer is subtracting fuel for a rich condition. If you were to fix your truck exactly then ST trims would instantly equal the opposite polarity of LT trims for net zero and both would walk towards zero over time.

So whats wrong? Either an actual lean or rich condition exists or a sensor is hosed and is presenting improper data to the PCM. Which is it? That's the $64,000 question. You either have a failed sensor(s) or you were running lean and the computer is adding fuel to keep the emissions low by keeping the air fuel mixture at 14.7:1 or stoichiometry. The most common causes of running lean are a vacuum leak (hoses, intake manifold, intake after the MAF) or a bad MAF sensor. Clean the MAF sensor if you haven't already, look for any cracked hoses or other evidence of a vacuum leak and then give us fuel trim numbers at idle, 1500, and 2500 - both banks, all 4 numbers including sign/polarity. If trims get better with RPM then we suspect a vacuum leak. Well get ya right eventually but bare with us, sometimes its obvious and sometimes its not so easy.

George

 

That is a good idea to follow. If - in your condition - it is possible to increase the RPMs on idle up to - let's say 3k RPMS and lookup the trims value it may help a lot. If the fuel trims are getting better it is likely the vacuum leak. If they don't - it could be an issue with fuel injection.
An important information could be when/how that all happened.