Okay, I've looked all over for something on this issue and I havn't found any useful or relevant info. I just did a cam, intake swap in may and about a week ago it started to stumble in all 6 gears between about 2500 and 3000 rpm. It will start there and get worse as you accelerate.The more gas you give it the worse it gets and will eventually stall out. I taped a fuel gauge to the windshield and the fuel pressure drops sharply from 60ish psi down to the high 30's and shoots back up. If you are very light on the throttle it will get to high rpms just fine. I replaced the fuel pump and nothing changed. It has the same codes that it had months ago which are p0101 and p0121. I don't really have any ideas. STFT on both banks is around +10 to +15 and LTFT is about +20. If I remember correctly this would mean it's running lean? The car idles fine and has no issue with starting. Any insight would be really appreciated.

 

has this been dyno tuned?

 

Yeah it was dyno tuned back in may when I did the swap.

 

I think I would start with having someone knowledgeable look at the tune and work from there.

 

Makes sense. It just seems weird that I would just now be having issues.

 

ya 2nd that and also verify all your plugs are good.

 

So fouled spark plugs could cause fuel pressure issues?

 

Nope, I would look at the fuel pump relay in the main fuse panel under the hood first. When the fuel pump starts going bad it puts more load on the relay causing it to overheat and slowly go bad. Second, I would look at the recently replaced fuel pump. Sometimes the O-rings don't get a good seal and will bleed off pressure especially on a returnless style fuel system and maybe the pump itself is bad. Another place to check is on the end of the fuel rail if it is stock, there will be a threaded fitting for checking pressure. It is like a valve stem on a tire. Cycle the ignition without starting the motor, you should hear the fuel pump prime for about 2 seconds, get out and push the bleeder on the valve and see if there is any air in the fuel line/system.

 

Thanks for the input guys. As it turns out it was the crank sensor. Never would have thought since the code wasn't thrown until it was pretty much completely gone.