The car is sputtering from time to time. When it does it always goes lean 16/1 + AFR. It is starting to idle at 16/1+ from time to time. I have done some searching because I keep think it is the fuel pump. I did change the fuel filter with no change. At idle fuel pressure is 40 psi. Take the vacuum line off of the FPR it goes to 45 psi. If it’s idle @ 40 and I gun it in park it goes to 45 and then to 35 quickly. From my searches it should be 43.5 psi but is 40 that far off? I haven’t taped the gauge to the windshield and tested WOT yet. But the reason I keep thinking it’s something else is because it comes and goes instantly. I could be accelerating and it’s sputtering and then it just catches and goes like normal. But I can always get it to do it if it is normal and then gun it and then cost for a few seconds then gun it again it will always sputter. I wouldn't think if the fuel pump was going it would start working like normal under load.?!? I keep looking for electrical issues or injector but am not sure. Has anyone had the same issue? Will a bad fuel pump just start working normal after not working? I’m confused.

Thanks in advance.

 

Never saw a fuel pump do what you describe.

It's best to look at what the O2's are reading Vs what the fuel trims are doing.

I had a problem with the passenger side O2 wires were burnt causing it to run lean under closed loop. However, it would gradually go lean until it bottomed out. Jump to open loop momentarily and then go back to closed loop and start the process over again.

It would also be a good idea to have the fuel rails/injectors professionally cleaned with something like the 3M cleaner I like to use. Remember, most fuel system problems will be a clog more so than a leak. Fuel sitting in the rails getting cooked right after the engine is shut down leads to deposits. Just a thought.

 

The specification for 43.5psi (41-47psi acceptable) applies to the measurement with the vacuum line off the FPR. Compare 43.5psi to 45psi that you measured. Within spec, at least at idle.

Lean O2's may be the result of misfires. Or it could be in intermittent error from the MAF sensor, indicating low air flow, which causes the PCM to supply less fuel.