Hey gang, this is my first post here. ive got a 2007 Dodge Nitro with a 3.7L (speed density system) that has excessive positive long term fuel trim numbers(14-17%) at idle on both banks. Short terms stay below +5%. I have checked fuel pressure, fuel condition, MAP, BARO, IAT, O2 and ECT sensor functionality and rationality. None of these indicate an issue. I can induce a rich condition (propane) or lean condition (removing vacuum line @ intake) and the fuel trims/o2 sensors respond appropriately. I installed a manual vacuum gauge to the intake to verify MAP readings as well. Initially i sprayed the intake and surrounding area with brake cleaner while watching fuel trims and O2 readings and found 2 vacuum leaks: at the PCV elbow and at the intake manifold gasket on the drivers side. I replaced these items and reset fuel trims and monitored scan tool data as before; this time, the fuel trim numbers gradually rose to about the same level of positive fuel trims as before, though not nearly as fast. While driving, these numbers are well within where they should be (+/- 10%). Considering this, im inclined to believe there is still a vacuum leak. I once again sprayed the intake and surrounding area with brake cleaner and whenever im spraying the back right corner of the intake manifold on the drivers side(basically on the EGR), fuel trims go very negative. I investigated the area and for the life of me i cant find the source of the leak. i removed the EGR to inspect, and i saw no problems. i even removed the EGR line to the intake and capped off the hole in the manifold to eliminate that as a source of a leak, but still nothing. i capped off the PCV valve and PCV hose with similar results. As i understand it, speed density fuel trims arent affected by air leaks (thats what i was taught anyway), but that doesnt seem to be the case here, as removing a vacuum line from the intake immediately causes the STFT and O2s to go positve, more than they already are. Whatever the issue is, its something that effects the entire engine, such as fuel supply or air intake, but im just not seeing it. Any help is appreciated.
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