How to fix the lean condition CEL codes on a supercharged VX?
I need to tap into the collective wisdom a little more directly than searching the forums. I found several references to these problems over the years, then posts claiming they fixed the problem by doing this or that, then more posts 2 weeks later saying the problem is back, so my forum research has been inconclusive. Plus, it isn't too clear which posters had a supercharger and which did not.
So, here are the relevant facts of the case...
1) I installed a supercharger last summer, along with a free-flowing exhaust. Whoo-hooo!! What fun! The bigger exhaust (2.5" from the cats back) helped as much as the S/C, by the way... it definitely improved torque off the line, whereas the S/C only helps the high end of the rev range.
2) Starting this winter, I have been getting check-engine lights fairly often. They are codes P0101 (MAF System Performance) and P0171/P0174 (Fuel Trim System Lean Bank 1/2). They keep coming back over and over, sometimes at idle when I start the engine, sometimes after being on the road for a while - there doesn't seem to be any pattern to it.
3) Sometimes the CELs are accompanied by an intermittent "stutter" of the throttle, and sometimes not. What I mean by that is that you hit the gas pedal partially, and instead of getting power, the engine kind of bogs down for a second or two, then the power kicks in. It is similar to the way the engine behaves when you are running out of gas.
4) The MAF code may be triggered by an out-of-spec reading on the MAF or the manifold absolute pressure (MAP) sensor, or from air/vacuum leaks in the intake. I replaced the MAF with an Autozone rebuild, but that didn't help at all. My mechanic tested the MAF and found that it was reading out of spec, but that doesn't mean much since the MAF that cured my 928 tested out of spec, too. Nevertheless, I will bring it back to Autozone and replace it. He checked for air/vacuum leaks but didn't find one. I have not checked the MAP sensor in any way.
5) My mechanic found that the throttle position sensor wire harness was loose, so he tightened/reattached it about 3 weeks ago. Since then, I keep getting the lean codes (P0171 & P0174), but not the MAF code (so far).
My mechanic and I are not sure what to try next. He keeps thinking in terms of the S/C kit is maybe not engineered right and these problems are part of that. I disagree, because I ran it with the S/C on there for about 6 months before I had any problems at all. I am suspicious of the fuel delivery system, and want to replace the fuel filter and fuel pressure regulator next. But before we start chasing our tails in a circle, I want to know if anyone here can provide some more conclusive advice.
So with all of that in mind, have you had this problem with your VX? Is it supercharged? How did you finally fix it?
Thanks in advance!
