bigmackloud

I'm getting a random lean condition at part throttle conditions. By lean I mean 16.0-18.0 AFR. Seems to linger longer than I would like. Occasionally it's bad enough to make the car run slightly rough. If I give it more throttle the mixture richens but as soon as I let off again it leans back out. Typically when this occurs the fuel pressure is in the 30-32psi realm. Problem seems to be completely random, doesn't always happen, though it is happening more often. General cruising AFR is 13.8-15.5. Full boost gets it down to the 10.7 realm.

Also, when I let off the throttle completely on decel, the AFR goes extremely lean. Like 28.0-99.0 AFR. Then after a few secs of that it might jump back to the mid 13s. Is that normal?

Idle is right around 1000-1100rpms. (It's been like this since I got the vehicle, not a new condition) At idle it pulls 10psi of vac. Decel at hwy speeds pulls ~17psi of vac.

Any idea what might be causing the lean conditions? Think I might have a throttle plate sticking or something?


Vehicle info:

2000 4.6L 2V. Vortech, heads, cams, 75mm MAF, Water Meth Injection, 60lb injectors, Boost-a-pump, long tubes, H pipe, flowmasters. Wideband AFR gauge. boost and fuel pressure gauges. accufab upper plenum, stock lower intake. other stuff but I think that's the most relavent.

Thanks

vanquish

I max out lean on decel too but it makes sense for fuel flow to stop when abruptly letting off the gas.