Announcement

Collapse
No announcement yet.

S14 hesitation at WOT

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #61
    Well I can say my car does not like the A/C on from a full stop, but doesn't stall out either. Could it be that your car just cannot hold the load? maybe your air compressor is just a little hard to turn? Having your A/C system charged too high can cause the compressor to bind a bit. The alternator bearings could be tight as well contributing to the problem.

    Question, If you tried & blipped the throttle to get the revs up before pulling from a stop with everything on can you pull away just fine?
    sigpic 95 M3 & 88 M3

    Comment


    • #62
      Low intake vacuum can be down to the following;

      1, Cam timing. More overlap=less vacuum as the downward stroke of the piston is pulling on both the throttles and the open exhaust valve. The A100 cam gear gives 6deg more overlap, not a huge amount and the 215hp, Evo2 and Evo3 cars run OK with them. Can you confirm that the cams are stock?

      2, Leaks. You seem to have discounted this however...

      Have you measured vacuum with a vacuum guage (not just the carb tune which is not scaled)? The validity of your vacuum reading can currently be questioned.

      Have you set up the TBs for the correct throttle stop position? Then set the individual throttle screws and the idle screw, all to the factory settings?

      Set the idle speed to the factory procedure?

      Only when all this is done, followed by a vacuum test can there be any validity.

      What are the compression numbers?

      Incorrect cam timing can also reduce compression pressure, too late intake closing reduces effective compression.

      If the compression and vacuum is good (the mechanical stuff), then you should move on to the fuel system.
      Sport Evo No.47

      My Sport Evo Restoration

      Comment


      • #63
        I believe with a blip, you can overcome the AC. The compressor seems to be the stock unit.

        I did think the bearing is going out, as the whine was occurring. Upon removal and then reinstall of the belt that was corrected. Without the AC belt, the pressure in the manifold stayed unchanged, i.e its not dragging down the engine and doubt it would as the clutch being disengaged should have the same effect.
        Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
        Past: '83 E28 533i/5 Schwarz/Schwarz

        Comment


        • #64
          Originally posted by stevesingo View Post
          Low intake vacuum can be down to the following;

          1, Cam timing. More overlap=less vacuum as the downward stroke of the piston is pulling on both the throttles and the open exhaust valve. The A100 cam gear gives 6deg more overlap, not a huge amount and the 215hp, Evo2 and Evo3 cars run OK with them. Can you confirm that the cams are stock?

          2, Leaks. You seem to have discounted this however...

          Have you measured vacuum with a vacuum guage (not just the carb tune which is not scaled)? The validity of your vacuum reading can currently be questioned.

          Have you set up the TBs for the correct throttle stop position? Then set the individual throttle screws and the idle screw, all to the factory settings?

          Set the idle speed to the factory procedure?

          Only when all this is done, followed by a vacuum test can there be any validity.

          What are the compression numbers?

          Incorrect cam timing can also reduce compression pressure, too late intake closing reduces effective compression.

          If the compression and vacuum is good (the mechanical stuff), then you should move on to the fuel system.
          1. The cams look stock, with stock notches. Short of pulling them out, I have not other way of verifying, i believe.

          2. Yes the procedure is followed down to the t. http://home.insightbb.com/~todd.kenyon/throttle.htm

          In fact, I redid the balance/sync multiple times, even made my own dial indicator holders for maximum precision. Photo attached.

          Also had the idle speed set per the procedure - TPS bridged, and reading with a handheld. I went over those procedures multiple times too. - http://home.insightbb.com/~todd.kenyon/idle.htm\

          It is an important fact to note, that the car came to me like this, before I started work on it. In other words, fixing the ITB sync/balance has brought nothing to the table.

          The only thing worth trying is A100 gear swap, back to stock.

          The fuel system is on a different set of pumps, and rock solid at 3bar, when driving and all. 100% certain that is also confirmed good.

          Compression numbers are 160psi all across.

          Where would you measure vacuum with a gauge?
          Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
          Past: '83 E28 533i/5 Schwarz/Schwarz

          Comment


          • #65
            Originally posted by Pavel View Post

            Where would you measure vacuum with a gauge?
            From the canister purge vac line.

            To be honest with you, the response to the throttle does not look too bad with AC off.

            If you hold the engine at 2000rpm and snap the throttle open to WOT, how does it respond?

            These engines are pretty highly strung compared to a modern engine or indeed a larger engine. What did you drive before this car?



            Sport Evo No.47

            My Sport Evo Restoration

            Comment


            • #66
              Originally posted by stevesingo View Post

              From the canister purge vac line.

              To be honest with you, the response to the throttle does not look too bad with AC off.

              If you hold the engine at 2000rpm and snap the throttle open to WOT, how does it respond?

              These engines are pretty highly strung compared to a modern engine or indeed a larger engine. What did you drive before this car?
              My experience with 3 other S14s is not similar - stock M3, 2.5 M3, and S14 swapped 2002 (with an aftermarket engine management). My personal cars are all 6 cylinders - S38, S50, M106. I have built two E28 M5s at this point. Hence the reason I donít believe the leakdown is the problem, but that is the only thing I can go by.

              The car drives fine at speed. I would actually say not bad at all. Response at 2k and to WOT is good.

              Not sure, but this is the first EVO geared + Dinan M3, and maybe that is affecting timing and idle vacuum.
              Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
              Past: '83 E28 533i/5 Schwarz/Schwarz

              Comment


              • #67
                When you say Dinan, what do you mean?
                Sport Evo No.47

                My Sport Evo Restoration

                Comment


                • #68
                  Originally posted by stevesingo View Post
                  When you say Dinan, what do you mean?
                  It has a Dinan Chip.

                  In the S38 world, the Dinan Chip paired with a Retarded setting on EVO gear, allows for the torque shift. The JimC chip was designed for the Advance setting of the gear - per Fahey. My understanding is there is no point in shifting the torque to the top in a S14.
                  Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
                  Past: '83 E28 533i/5 Schwarz/Schwarz

                  Comment


                  • #69
                    Do you know how much ignition advance it runs at idle?

                    I think we may be on to something here.

                    If the ignition is retarded, then for a given load, you need more air. More air is needed the lower the vacuum.
                    Sport Evo No.47

                    My Sport Evo Restoration

                    Comment


                    • #70
                      Originally posted by stevesingo View Post
                      Do you know how much ignition advance it runs at idle?

                      I think we may be on to something here.

                      If the ignition is retarded, then for a given load, you need more air. More air is needed the lower the vacuum.
                      That is an interesting point! I wonder if that is available anywhere, as a spec for the chip.

                      I personally have noticed no difference off idle on a S38 with Evo gear Advanced with stock chip, Jim C, or Dinan. I have tried all three chip variations, on the same engine.

                      Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
                      Past: '83 E28 533i/5 Schwarz/Schwarz

                      Comment


                      • #71
                        Put a stock chip in and try it.

                        I don't have any faith in chips. Ill the advance curves I have seen over the years are obviously over advanced. No wonder there are so many big end bearing failures.
                        Sport Evo No.47

                        My Sport Evo Restoration

                        Comment


                        • #72
                          It's a cheap test, worth a try. I did test with a different ECU, very early in the game but w/o knowledge if it had stock chip or not. Thanks for the suggestion.

                          Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
                          Past: '83 E28 533i/5 Schwarz/Schwarz

                          Comment


                          • #73
                            Hi Pavel,

                            what a frustrating issue. Hopefully you Can find the problem soon!

                            Comment


                            • #74
                              Did you try to change your coil?

                              Comment


                              • #75
                                Been thinking about this. I've had over the years bikes and cars with low compression/bad rings that have similar symptoms to you. Like under any type of load (ie AC on) the engine would die once clutch is let out. At high revs the engine would operate fairly normally.

                                Low compression = low torque.
                                Your leakdown figures and compression figures are to me obviously an issue with this engine. 160 psi compression? Mine was 230 after a rebuild, and that's a common figure for s14s. 160 psi is stock figures for a e30 325i M20 engine, which has 8.8:1 compression from factory.

                                Also your leakdown figures of 25-30% to me indicate an issue. I regularly do leakdowns at work (I am a BMW technician) and the norm for a engine with no issues is 5 or 10%.

                                You have replaced everything on the engine... Maybe address the mechanical issues and retest after. Ie new rings.

                                Comment

                                Working...
                                X