Rich Fuel Trims, Lean on Wideband

[jlado13]

So, my STFT bounces between -10 and up to +4 or so. LTFT is down around -12. It is my understanding that these are telling me I'm running rich under anything except WOT. However, I have a lean idle (17's on the wideband) and cruise ranges from 14.7ish to 15.8 or so on the wideband. Could this indicate a vacuum leak or something?

Even if it was a vacuum leak, wouldn't my fuel trims be positve, since the front 02 sensor would tell the ECU to "add" fuel? I'm lost.. Any help is greatly appreciated.

Jordan

 

[2gGSX]

Exhaust leak before the wideband will cause this, I have the exact same problem due to a slight leak at the flex section of my downpipe. Adjust according to LTFTs.

 

[Rob10_99]

Goes without saying if your talking about fuel trims.... boost leak test yet?

 

[jlado13]

I have done a boost leak test. I have a leak around the TB area, but can't pin point it yet! I'm getting frustrated. I've used soapy water and what not to no avail.. I'll just have to keep on it til I find it I guess.

But wouldn't Fuel Trims reflect a leaner condition if the leak under vacuum was big enough?

Thanks for the info about the exhaust leak btw..

 

[steve]

Keep in mind that we are talking about leaks before the cylinder and leaks after.

Any exhaust leaks within a few feet of the O2 sensors are going to throw off their readings.
The fact that your wideband reads lean at low exhaust flow (idle) but normal at cruise implies that you might have a exhaust leak that is allowing fresh air to reach the sensor.

The fuel trims are saying that your tuning is rich. Have you been playing with your tuning based on the WB readings?

 

[jlado13]

Ok thank you Steve. I have mostly been doing WOT tuning with my logger and trying to keep the wideband at 11:1. So yes, I have been using the wideband while monitoring my timing curve on the logger. I have done minor Lo throttle tuning with the AFC and fuel trims, but think I need to get that boost leak fixed before I tune any further. There is no doubt in my mind now, that I'm tuned rich. This being the case, it should be perfectly safe to wait to get into this "Leak hunt" until the weekend, correct?