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Rich (negative long term fuel trim) causes

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here Rich (negative long term fuel trim) causes

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  • #1025302
    Taylor MauldinTaylor Mauldin
    Participant

      Hi. I have a 96 camry federal 2.2 auto with 307k miles. The short term fuel trim is in stoichiometry but the long term sits around -25. Holding the revs at 2500 improves the long term to -17.

      My question is what all could cause this?

      I have already replaced all sensors, air filter, purge valve, thermostat, fuel pressure regulator, and the fuel injector cleaning guy said the injectors are not leaking down.
      Tested the old and new sensors and all are good. The fuel pressure is also in tolerance.

    Viewing 11 replies - 1 through 11 (of 11 total)
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    • #1025314
      Rahul JonesRahul Jones
      Participant

        Try disconnecting sensors like MAF sensor and Throttle Position Sensor then check if the reading changes. Also, you can check if the exhaust fumes reduces or not.

        #1025315
        Taylor MauldinTaylor Mauldin
        Participant

          Disconnecting sensors causes no changes

          #1025318
          Rahul JonesRahul Jones
          Participant

            Is it possible to share the live data reading from MAF, MAP, TPS, and oxygen sensors?

            #1025319
            Taylor MauldinTaylor Mauldin
            Participant

              Have to manually type in. It has a map but no maf.
              Engine at warm operating temperature idle 750
              Tps 11.4 %
              Map 3.9-4.1 psia
              Ect 200f
              Iat 85f
              Oxygen upstream oscillates from .1-.9 back and forth rapidly, upstream short term trim oscillates between 3% rich 1% lean, upstream long term trim -25 % rich, downstream stuck at .115 v sometimes it unsticks and fluctuate between .1-.3 v

              #1025327
              Rahul JonesRahul Jones
              Participant

                Is your MAP reading positive on idle? It is supposed to be negative on idle as the intake has vacuum.

                #1025331
                Taylor MauldinTaylor Mauldin
                Participant

                  The map is reading correctly. 29.4 inhg map atmospheric – 8.0 map at idle= 21.4 inhg vacuum

                  #1025334
                  Rahul JonesRahul Jones
                  Participant

                    My next suspect would be a stuck open EGR valve. You can plug the vacuum hose going to the EGR and see if that improves.

                    #1025337
                    Taylor MauldinTaylor Mauldin
                    Participant

                      Plugging the hose made no difference

                      #1025341
                      Rahul JonesRahul Jones
                      Participant

                        Do you have anything to check the fuel injector pulse duration or through OBD live data? I had a similar issue with a customer’s car where the datas were normal but the engine ran rich and failed emissions. That was caused by a faulty ECU giving longer pulse to the injector.

                        #1025347
                        Taylor MauldinTaylor Mauldin
                        Participant

                          No, I don’t. The ecu is almost new , it only has 2000 miles on it

                          #1025352
                          Rahul JonesRahul Jones
                          Participant

                            At this point, I am helpless. Sorry, hope someone from this forum can help you out.

                          Viewing 11 replies - 1 through 11 (of 11 total)
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