QuestionQUESTION: I have an 01 Santa fe 2.4 constant po171 fuel trim get leaner with rpms maf reads 1.39 v at idle gets higher with rpm.swaped with known good maf same readings. o2s read good,no vacume leaks with smoke checker.belows ok.any ideas??
ANSWER: Since you have a known good air flow sensor at your disposal, make a chart and compare their readings. It doesn't take much variation to set a P0171, so the trend of increasing values as rpm increases isn't a good indicator.
For each air flow sensor, take air flow and tps readings at several rpms. Be sure to use the same rpms for each sensor. Select something like idle, 1000, 1500, 2000, 2500, 3000, 3500, and 4000 as your rpms. Use the TPS as a check to verify that you have approximately the same throttle opening. In general, presuming you're using the voltage scale you've given above, if the readings vary by more than 0.05V between sensors, one of the sensors is defective.
---------- FOLLOW-UP ----------
QUESTION: they are almost = the fuel trim is 20
at 50 mph could it be the fuel pump?motis troublee shooter says maf should read .5v at idle is reading 1.39?
ANSWER: Is the 20% fuel trim from the freeze frame data or from the current data when you're driving the car?
In reference to the specification you have, it's probably wrong. Although it was likely taken from Hyundai's service information, which indeed indicates that 0.5 is the normal air flow voltage at idle, these sorts of things are notoriously often incorrect in Hyundai's service information. I have printouts of actual data from various models and engines, and the closest I have to your vehicle is a 2003 Sonata 2.4. To my knowledge, the air flow sensor and engine is identical to yours. According to this printout, the voltages were 1.43V at idle and 1.99V at 2500 RPM.
I also have some difficulty with the language "almost equal." You're typically looking for a small variation which is worse at higher rpms. Exactly how close are the values at the different rpms?
---------- FOLLOW-UP ----------
QUESTION: the 20 is live data.the "almost =" is =/- .01 through the range of rpm idle to 4000.I had to return the known good maf this thing is making me crazy.The exhaust manifold was changed due to a crack and every thing was good for a month
AnswerThose are defintely close enough. If you haven't done so yet, you should probably check fuel pressure. If the fuel pressure is too low, the ECM will need to hold the injectors open longer than expected in order to achieve the proper fuel mixture, making the ECM set a lean condition code.
