Background leading up to the beginning of power loss/drop:
I have been receiving the P0171 and P1074 codes that have been set on and then set off.
The entire intake air section has been checked for leaks using water and Starting fluid, no signs in the change of engine RPMS.
I have lived with this lean condition for 12 months.
2 months ago I had a failure with one of the AFM hydraulic lifters and had to pull the heads and replace all lifters and the VLOM with new equipment.
At the same time, the fuel injectors were replaced with refurbished Delphi parts. The COP and spark plugs were replaced. The mechanical part is working very well.
I checked the cylinder compression and they register 180 pounds, the same as before the heads were removed.
After resembling all the pieces, I had the oil pressure sensor stop working, installed a new oil pressure sensor and that was the end of that problem.
This is all the repairs/updates done prior to the sudden power loss/drop
I am dealing with the same lean OBD2 codes (171/174) plus a new issue
) that has been impossible for me to locate the cause of this problem:
This power loss/drop is the reason for this post.
I can drive the Trailblazer for 5-10 minutes will get the expect acceleration power and then there is a power loss/drop.
The engine does not accelerate when pushing the gas pedal down and there is some popping in the intake system, which I take this as a sign of lean fuel.
I did not have this issue before removing the heads and replacing the hydraulic lifters.
My first thought was a fuel pump overheating so I hooked up a fuel pressure gage and did the same driving test. The gage shows a pressure of 62 pounds and did not flinch when accelerating.
When the power loss occurred there was no drop in fuel pressure on the gage.
Well darn, I was hoping to fix these 2 issues with a new fuel pump.
In using my scan tool I observed these indicators values when the engine runs well:
O2 Sensors will vary from .1 to .8 volts.
The long term trim% is very high 27-30% always
The short term trim% is very high (21-25%) frequently and sometimes in the negative area. In most cases the SFT% is high when driving; it goes down when in park.
The MAF shows 8.7-9.6 reading when at idle and while driving at around 2000 rpms the reading 70-75.
The fuel tank pressure holds steady at .1
When the power loss/drop occurs I see these reading on the scan tool:
O2 sensors are stuck at .0 to .1 - all 4 of them
The STFT goes to zero and stays there, the LTFT drops to below 20%,
Seems like something has caused the fuel feed to be an idle mode rate, no Limp mode indicator is on.
The MAF rate makes sense with the RPM, which are dropping
In looking at the data log I noticed the EVAP reading changed from -770 to +2.5 and stays positive until the engine is shut off – Why??
This power loss does not go away until I turn off the engine and let it sit for 3-5 minutes, the longer the engine is off, the longer I can drive before the next power loss occurs.
The CEL did not flash.
No new OBD2 codes are set, just have the P0171 and P0174.
To me, this points to a fuel pump overheating, BUT the fuel pressure did not drop 1 bit.
Where do I go next to solve this sudden power loss/drop??
Thanks for any guidance on my power loss problem