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Swapped 3.4DOHC wants to die when shifting

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  • Swapped 3.4DOHC wants to die when shifting

    I recently purchased a Fiero that the previous owner had modded by having a 3.4DOHC engine swapped in. I must say that I like the power and that the fuel mileage is just about the same as the 2.8 it replaced.
    It does, however, have an issue I'm trying to track down. The engine wants to die between shifts especially downshifting. It starts just like it should, high idle when cold and thens drops after warming. If I just let is sit there the car idles like it should.
    The engine is out of a '93 Lumina Z34. It is mated to the Getrag 5 speed. I believe the donor was an auto.
    I emailed the builder and got more info. The intake is from a '97 and the throttle body is from an LT-1 350. The ECM is from the donor car.
    The chip was done by Ryan at Sinister Performance. And I've emailed him about this issue also. He seems to think it might be a electrical/sensor issue after I took a log of a run with TunerPro RT that he looked at for me.
    I've cleaned the battery connections. Checked to make sure other wiring connections are tight.
    No stored codes. I've already tried the IAC and that's not the culprit. Ryan did tell me that the log I sent him showed the IAC counts not dropping below 59. I did find and fix a vacuum leak. If there are more I haven't found them yet.
    Anyone have suggestions on what to do next?
    One thing I need is the sensor locations. I have a Haynes manual but the only engine that ISN'T shown is the 3.4DOHC. Does someone here have a picture/schematic showing where the various sensors are located on this engine?
    I'd also like a vacuum hose routing to make sure things are where they are supposed to be. Or to compare how it should be to what it is as modded.

  • #2
    Vacuum leak or fuel pressure regulator

    96 Z34 3.4 SC DOHC Getrag, 284 5sd manual transmission, stage 3spec clutch, 97 engine, 97 pcm, S3 intercooler 1 of 1 Roots SC LQ1 in the world 8.5 psi.

    Comment


    • #3
      High idle then dropping to normal after it warms up sounds like LIM gaskets to me (vacuum leak). I didn't realize the 96/97 intakes had that issue though. I know for a fact from experience the 91-95 intakes did though. Could spray a little carb cleaner in between the LIM and heads when it is cold to see if you get a change in idle. How is your brake assist when cold?

      I would PM robertisaar for the vacuum diagrams.
      -60v6's 2nd Jon M.
      91 Black Lumina Z34-5 speed
      92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
      94 Red Ford Ranger 2WD-5 speed
      Originally posted by Jay Leno
      Tires are cheap clutches...

      Comment


      • #4
        done.

        http://i.imgur.com/M8tIg.png
        1995 Monte Carlo LS 3100, 4T60E...for now, future plans include driving it until the wheels fall off!
        Latest nAst1 files here!
        Need a wiring diagram for any GM car or truck from 82-06(and 07-08 cars)? PM me!

        Comment


        • #5
          Thanks for the diagram.
          Fuel pressure - no schrader valve on fuel rail.
          LIM vacuum leak - sprayed brake clean around LIM. No change in rpm. Sprayed around throttle body gaskets. No change. Sprayed around goose neck to manifold. No change. Sprayed around TPS and IAC. No change.
          Any more ideas?

          Comment


          • #6
            Originally posted by dedgar View Post
            Thanks for the diagram.
            Fuel pressure - no schrader valve on fuel rail.
            ?? It should if its a 96 its on the front of the rail or if its a 91-95 rail it would be next to the power steering pump. But the random stall on decell of me was a fuel pressure problem.

            96 Z34 3.4 SC DOHC Getrag, 284 5sd manual transmission, stage 3spec clutch, 97 engine, 97 pcm, S3 intercooler 1 of 1 Roots SC LQ1 in the world 8.5 psi.

            Comment


            • #7
              Engine was swapped into a Fiero. Things got deleted. Like the power steering.
              Also the engine is a '93 and the intake a '97. I didn't do the build or the swap. I bought it like this. Now I'm trying to sort it out.
              The vacuum diagram that was provided isn't anything like what is on the engine at this time.
              Tomorrow after I get back from a doc appt. I'll take some pictures and make a diagram of the installed vacuum hose routing.

              Comment


              • #8
                Originally posted by dedgar View Post
                Any more ideas?
                Unlit propane torch. You can use it around vacuum lines to find a leak like you did the brake clean.

                Sent from my HTC One X using Tapatalk 2
                -60v6's 2nd Jon M.
                91 Black Lumina Z34-5 speed
                92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
                94 Red Ford Ranger 2WD-5 speed
                Originally posted by Jay Leno
                Tires are cheap clutches...

                Comment


                • #9
                  Pictures of each end of the fuel rail. No schrader.
                  http://i272.photobucket.com/albums/j...z/DSC_0024.jpg
                  http://i272.photobucket.com/albums/j...z/DSC_0021.jpg

                  And yet another thing, the fuel pressure regulator is integral to the fuel rail. It doesn't come off that I can tell.
                  So back to the builder to ask about this.

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                  • #10
                    I think I have the fuel rail figured out. It appears to be from the '97 era engine. The schrader valve in located in the middle of the rear rail.
                    The way the intake is on this engine, that valve is now covered up by the UIM.
                    I also see the regulator is held in place by an internal snap ring. More tools to buy as I don't have the right pliers.
                    Last edited by dedgar; 08-17-2012, 01:54 PM.

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                    • #11
                      And here is what I have for vacuum routing.
                      http://i272.photobucket.com/albums/j...7vrz/34vac.png

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                      • #12
                        New regulator installed and died pulling out of driveway. So still a problem.
                        I'm starting to lean to chip tune or ECM problem.

                        Comment


                        • #13
                          i know how a lot of other people feel about Ryan's work..... it is a possibility.

                          i would think even a stock LQ1/5 speed tune would be at least drivable, if not optimal.
                          1995 Monte Carlo LS 3100, 4T60E...for now, future plans include driving it until the wheels fall off!
                          Latest nAst1 files here!
                          Need a wiring diagram for any GM car or truck from 82-06(and 07-08 cars)? PM me!

                          Comment


                          • #14
                            Originally posted by robertisaar View Post
                            i know how a lot of other people feel about Ryan's work..... it is a possibility.

                            i would think even a stock LQ1/5 speed tune would be at least drivable, if not optimal.
                            I've heard the same about his work. Out certainly couldn't hurt to try some BCFA goodness.

                            Sent from my HTC One X using Tapatalk 2
                            -60v6's 2nd Jon M.
                            91 Black Lumina Z34-5 speed
                            92 Black Lumina Z34 5 speed (getting there, slowly... follow the progress here)
                            94 Red Ford Ranger 2WD-5 speed
                            Originally posted by Jay Leno
                            Tires are cheap clutches...

                            Comment


                            • #15
                              "BCFA goodness" ?? I don't know "BCFA goodness". Elaborate please?
                              When I bought the car the po listed the tb as N*. When I emailed the guy that built it he said the tb was LT-1. So who knows what Ryan was told (or not told) and tuned for.
                              I'll ask again. Does anyone have a picture/schematic that shows where the sensors are on the engine. I've located the IAC obviously since I've changed it. MAP, I'm pretty sure I've found. The TBS and O2 are also easy. How about the rest of them?
                              If a sensor or three are miss reading it could throw a curve to the ECM. I can't test/replace them if I can't find them.

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