Lean Codes P0171 and P0174

[Jerome]

So... I have a 96 SHO with the cams welded and its putting out lean codes. I've done a smoke test and found no vacuum leaks. Changed the fuel pump, filter and regulator about 5000 miles ago. Has new cam and crank sensors, new coil packs and plugs, cats and two of the O2 sensors. The performance is good, but I can't figure out what it might be. Any ideas?

 

[gamefanatic]

Still a lot of possibilities.
- Check fuel pressure. If you have an ODB2 reader, monitor this at different loads. When you whip the throttle does it drop at all? Could be issues with Injectors.

- Make sure MAF sensor wire is cleaned. You may need to lightly scrape it with a flat head in some cases.

- Check for head gasket leaks. This can be an early sign. Just be aware you might not get a reading using a fluid block checker. You should be seeing other signs like overheating under load, loss of water.

 

[gamefanatic]

One thing I forgot to mention was plugged / failed Catalytic Converters. You might be able to get some info on this from a shop or if you visited a friendly SMOG check place. Otherwise you would need to pull the CATs out and see if they are in good shape. IE) Not plugged, disintegrating.
With our cars there are 3 CATs so for them to puke out bad air shows and issue.
Again if you have access to a ODB-II / Troubleshooting Computer you can usually diagnose this symptom without even cracking a bolt or knuckle....