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rich stutter and 13mpgs

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    #1

    rich stutter and 13mpgs

    Where do I start,

    Was running a boosted m20 but blew it up, can't afford to fix it right now so I swapped in a known good stock motor

    I'm getting a rich stutter that happens in all driving conditions (idle, cruise, accel, and deccel) doesn't matter if the car is warm or cold, though it seems to happen more often when cold.

    So far I've replaced injectors with m50s do to the stockers making the motor excessively lean (had af gauge hooked up and was reading 18afrs on acceleration..

    Replaced the cps with a clean, known good one. No fix

    Changed out cap and rotor with a good one. Seemed to clean up my idle a bit but still now fix

    New o2 sensor. No fix

    Fuel filter is new

    Thermostat is a 75 degree but I don't feel like it would be a problem

    Only thing not hooked up is the charcoal canisters but don't think that would be a problem either because I thought those where just a emissions thing. Either way the sensor that goes from the hose off the bottom of the tb to the charcoal canister is hooked up.

    Need some input because this 13mpg is killing me lol got better mpgs when I was boosted with 60lbers


    Originally posted by LowR3V'in
    It's in the name e30tech not e30offtopic
    Tags: None
    #2
    What is the rail fuel pressure at idle and while driving?
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment

      #3
      Originally posted by jlevie View Post
      What is the rail fuel pressure at idle and while driving?

      38-40psi

      Comment

        #4
        Check the thermo sender on the thermostat the one that sends reading to the computer not the gauge. It's probably out of range and sending a false signal. The computer sees a different signal than what you see on the gauge.
        https://www.facebook.com/BentOverRacing

        Comment

          #5
          Originally posted by M-technik-3 View Post
          Check the thermo sender on the thermostat the one that sends reading to the computer not the gauge. It's probably out of range and sending a false signal. The computer sees a different signal than what you see on the gauge.

          Blue coolant temp sensor? I suppose thats the one you are talking about. We have a few laying around so I tell him to try that if he doesnt see this. Im thinkin he already swapped that the other day but Im not certain.

          Comment

            #6
            Did you check the ohm range to see if it was functioning properly?

            He made no mention of the coolant sensor. Just a thermostat. That is first place I would look.

            My car is running cold because a sticking open thermostat so this is why I'm getting poor fuel mileage. I discovered it the other day. But it shows on the gauge.
            https://www.facebook.com/BentOverRacing

            Comment

              #7
              Originally posted by M-technik-3 View Post
              Did you check the ohm range to see if it was functioning properly?

              He made no mention of the coolant sensor. Just a thermostat. That is first place I would look.

              My car is running cold because a sticking open thermostat so this is why I'm getting poor fuel mileage. I discovered it the other day. But it shows on the gauge.

              Nope havent checked ohm range yet.

              Comment

                #8
                Check it bet it's out of range. Have seen new ones not even close to spec.
                https://www.facebook.com/BentOverRacing

                Comment

                  #9
                  38 at idle and 43 with an open throttle is correct for an M20B25 engine. That is what is in the car, right?

                  Seeing 18:1 AFR with the stock injectors means; low rail pressure, clogged injectors, bad AFM, or bad DME. The fuel pressure is correct. If the AFM vane moves freely and no one has twiddled the clock spring tension. Those two can be removed from the scan. That leaves the injectors or the DME. Of the two I'm more inclined to suspect the DME as I have seen it cause a high AFR (greater than 14:1) too many times.

                  BTW: The apparent rich condition and low fuel mileage could be from partial lean misfires, which would also explain the stutters.
                  The car makes it possible, but the driver makes it happen.
                  Jim Levie, Huntsville, AL

                  Comment

                    #10
                    Originally posted by jlevie View Post
                    38 at idle and 43 with an open throttle is correct for an M20B25 engine. That is what is in the car, right?

                    Seeing 18:1 AFR with the stock injectors means; low rail pressure, clogged injectors, bad AFM, or bad DME. The fuel pressure is correct. If the AFM vane moves freely and no one has twiddled the clock spring tension. Those two can be removed from the scan. That leaves the injectors or the DME. Of the two I'm more inclined to suspect the DME as I have seen it cause a high AFR (greater than 14:1) too many times.

                    BTW: The apparent rich condition and low fuel mileage could be from partial lean misfires, which would also explain the stutters.
                    Yes stock b25, fuel at the rail is correct. It was only lean with the stock injectors though, now it is fine with the 17.5 lbers in it so I am pretty sure the stock ones were clogged.

                    Comment

                      #11
                      Will have to check the blue sensor, its a rich missfire, and that's confirmed with a afr gauge. The dme could be bad but don't have another to check it with at the moment


                      Originally posted by LowR3V'in
                      It's in the name e30tech not e30offtopic

                      Comment

                        #12
                        What is the AFR now? I wonder if the O2 sensor might not be bad. If everything else was right the M50 injectors would make the engine run a little rich until (using data from the O2 sensor) it adapted to the greater flow.
                        The car makes it possible, but the driver makes it happen.
                        Jim Levie, Huntsville, AL

                        Comment

                          #13
                          Normal under all conditions but the rich stutter.. its a brand new bosch sensor


                          Originally posted by LowR3V'in
                          It's in the name e30tech not e30offtopic

                          Comment

                            #14
                            If the AFR is normal, I don't see how the engine could be experiencing rich stutter. Something else must be going on. Does the tachometer or econometer react when the engine is stuttering?
                            The car makes it possible, but the driver makes it happen.
                            Jim Levie, Huntsville, AL

                            Comment

                              #15
                              It's a rich stutter, I can smell fuel for a few seconds afterwards. Car will be completely fine then it stutter go to about 11.5-12 for a sec and everything is completely back to normal. Rpms and eco stay still


                              Originally posted by LowR3V'in
                              It's in the name e30tech not e30offtopic

                              Comment

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