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    eta Fuel Pressure Question

    Without giving you guys an overly long story, hoping you can confirm the fuel pressure readings I am seeing are as they should be. Background is that I am trying to get my semi-recently acquired '86 eta automatic to pass smog. It's very close, passes everything easily except high NOX at 25 mph - just over the limit. This lead me to looking into the fuel system as that's normally a lean condition, and the car was sitting for a couple of years before I bought it so I figured the fuel system could be a bit gummed up.

    After throwing a bunch of parts at it, I am now seeing 30 psi at idle, which bumps up to 36 with any appreciable load. Is this correct? Bentley tells me I should have 36 psi (or 2.5 bar) all the time, but I only reach that under load, with idle and light load coming in at 2 bar.

    FWIW, I have already replaced the FPR, fuel filter, and high pressure fuel pump. Injectors are fresh rebuilds from RC engineering. I have not re-smogged since replacing the FPR and pump, but want to confirm the pressure readings I am seeing are correct. Can anyone advise?

    #2
    It could be your O2 sensor and Id check the TPS if the problem is at idle
    Seat Shocks....I have passed the baton to John Christy from Ninestitch. Email John or Garrett at ninestitch1@gmail.com

    https://www.r3vlimited.com/board/sho...86#post4944786
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    http://www.r3vlimited.com/board/showthread.php?t=360504
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    Comment


      #3
      O2 sensor is new Bosch, so thats not the issue. There is no "problem" at idle, car runs great and idles very smoothly. I'll test TPS but based on how the car runs I can't imagine that's an issue. I'm just wondering if these fuel pressure readings are normal.

      Comment


        #4
        then i could say you may have clogged lines or improper functioning regulator.
        both would cause a lower pressure. out of curiosity, does the manual say the pressure should rise to something above 36 under load? because then you would be under pressure under both circumstances. leading me to further believe it is one of the two causes mentioned.


        you poor soul. no other state makes people smog a 30+ year old car.

        Comment


          #5
          Uh...

          Unhook the vacuum line from the regulator, and watch the pressure hop up to 2.5 bar.

          The regulator is referenced to intake manifold pressure, while your gauge is referenced
          to atmospheric. When you pull the vacuum line, you now reference the regulator
          to atmospheric, like the gauge, and get an accurate measure of fuel pressure.

          t
          now, sometimes I just mess with people. It's more entertaining that way. george graves

          Comment


            #6
            TobyB - That makes sense, kinda. I already tried that, and yes, I actually get slightly over 2.5 bar at idle with the vac line disconnected.

            So, that being the case, you're saying the behavior I am seeing is normal and as it should be, yes?

            Comment


              #7
              Seems right to me, we’ve got an ‘87eta and the fuel pressure with new pump and regulator. Also, if you pinch the fuel return line with your finger you will see the pressure spike really quickly. I suppose you could forceably pinch the line with a clamp and force the system to run around 45psi but I don’t know if that would help pass the car, probably isn’t legal for you to alter it like that.

              Years ago I had a ‘91i and in order to pass smog in Memphis I had to have my mechanic make an adjustment. Whatever he did made the car run low on power and it was horrible to drive. Then I would go back and he would undo whatever he did. Sadly, this was before I knew anything about the m20, I just drove the snot out of my beloved coupe.
              My son has the 1987 325e, 2 door, 5speed
              I daily the 1989 325i, 4 door, 5speed

              Comment


                #8
                Yuppers, 2.5 with no vacuum is what the spec is supposed to be.
                If it's 2.55, that's not your problem with emissions. If it's 2.75,
                that might be just enough to push you over. In theory the o2 sensor
                could fix that, but if other things have drifted, it might...


                all I got,

                t
                now, sometimes I just mess with people. It's more entertaining that way. george graves

                Comment


                  #9
                  Hey guys,
                  Just a follow up here - finally got the car back over to my smog guy and it passed with flying colors. It blew super, super clean - so, long story short, the fuel pump was going soft - it still provided enough fuel for the car to run pretty normally, just slightly lean. Thanks for the input, glad to have her back on the road!

                  Comment


                    #10
                    Originally posted by Nosser View Post
                    Without giving you guys an overly long story, hoping you can confirm the fuel pressure readings I am seeing are as they should be. Background is that I am trying to get my semi-recently acquired '86 eta automatic to pass smog. It's very close, passes everything easily except high NOX at 25 mph - just over the limit. This lead me to looking into the fuel system as that's normally a lean condition, and the car was sitting for a couple of years before I bought it so I figured the fuel system could be a bit gummed up.

                    After throwing a bunch of parts at it, I am now seeing 30 psi at idle, which bumps up to 36 with any appreciable load. Is this correct? Bentley tells me I should have 36 psi (or 2.5 bar) all the time, but I only reach that under load, with idle and light load coming in at 2 bar.

                    FWIW, I have already replaced the FPR, fuel filter, and high pressure fuel pump. Injectors are fresh rebuilds from RC engineering. I have not re-smogged since replacing the FPR and pump, but want to confirm the pressure readings I am seeing are correct. Can anyone advise?
                    You stated in your original post that you had replaced the high pressure pump ?Does this mean your new pump was a failure?

                    Comment

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