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S14 hesitation at WOT

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  • #46
    Originally posted by Pavel View Post
    So a little update. I tried known good fuel and main relays, no difference. Checked resistance on the ref sensors, seemed fine. The chassis grounds checked fine.

    Next I found the first smoking gun - i swapped the CAT (had a whole exhaust laying around with a different CAT and rear muffler) the car drives amazing at speed, no more bog downs past 80 or above 4000RPM in 4th. Goes happy to the red.

    The hesitation from idle to WOT, or partial throttle, remains. I unplugged the ECU overnight, and there was definite improvement. Now when i disconnect the CTS the car actually revs up, but takes it a couple of seconds to really rev-up in closed loop.

    The AC being ON has an effect on the idle to 1200RPM response.

    I believe it's a vacuum leak, so far I can only get the carbtune to read around 12cmHg when syncing the ITBs. I am going to try next what.

    I think video helps the best.

    Here is the symptoms w/o AC and with AC.

    https://www.youtube.com/watch?v=hD_d2P0Mqjw

    Here is the vacuum reading at the ITB

    https://www.youtube.com/watch?v=pFyH5XPzLBs

    It might be time to adjust the AFM spring tension. And also re-read this whole thread and redo all the measurement steps.
    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


    • #47
      Hi,
      Just recapping the problem (down on power) first arrived after the valve were adjusted:
      How were the valves adjusted what tooling was used to compress the bucket and what were the clearances set to?

      Was the cams removed during this process and has the cam timing been checked, just thinking of the low manifold pressure.

      Down on power is how I would describe the engine performance from watching your video:
      With the A/C on the engine has trouble trying to accelerate.

      Please post a video of the AFM boot while the engine accelerates as it is a known problem of sucking in and collapsing.


      After the good work you have done so far eliminating various things, I think think there is a need to get back to the basics and recheck a few things
      Valve clearances, cam timing, compressions ( I would expect better than 200 psi on a hot good condition engine)
      Fuel flow, AFM (Just try another one Dont fiddle with the spring)

      You would have to try that manifold gauge on another S14, usualy modern engine has 17inch of mercury, if on another S14 you get 17 inch mercury that would also point to low mechanical efficiency of the engine ie low compression or cam timing out.
      Dave




      E30 M3 1987
      Mini Clubman GT
      BMW E36 323 Msport
      Toyota Corona
      KTM 200EXC
      Honda CB50 (1979)

      Comment


      • #48
        I agree with Dave. That’s a solid advice going back to the valve adjustment and how it was done.

        What did the leak down test show?

        What flow in the fuel return pipe? Should be 600 or 750cc in 30 sec)
        What fuel pressure did you measure?

        Comment


        • #49
          I would def throw a fuel pressure regulator at it just for ha-ha's.

          Comment


          • #50
            I think the leak down may give us the smoking gun...

            Comment


            • #51
              Been travelling for the past few weekends - USGP F1, local BMW event, wedding so had to pause on the car.

              Should be resuming Saturday with leakdown and timing check. And making a list of all the steps taken so far, and redoing some of the tests.

              The valve adjustment was validated by me a few months ago, and was done in spec. Cams were not removed.
              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


              • #52
                Finally, the long awaited timing verification and leakdown numbers

                What you will see in the timing photos is that the exhaust cam is off (retarded). At first I was worried, however I immediately thought about A100 gear. I am pending confirmation from owner if he bought it modified. I am almost certain it is. The stamping of the gear is on the inside, and most probably covered by the lock washer.

                Another reason to think, it is a A100 are the leakdown numbers, and the yellow mark on the cam, where the stock gear would align it.

                A quick search on here, shows that this is the correct placement of the exhaust cam with A100, in retarded. I was worried at first, because with my S38 experience that is one tooth off.

                Cyl 1) 20%
                Cyl 3) 35%
                Cyl 4) 30%
                Cyl 2) 30%

                I believe all is good in this department.
                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


                • #53
                  I just realized these numbers are on cold engine. Silly me. However, at operational temp i think they would drop even further. Currently validating engine harness from devices to ECU - AFM, TPS, Reference Sensors, CTS, ICV, O2 sensor, Injectors, AC compressor (once again).
                  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


                  • #54
                    It is good I remembered to check my NIB A100 gear for where the stamp is. It wasn't that bad to validate, after all. Took a little bit of "searching".

                    I say timing is good. Leakdown on cold engine are ok as well.

                    Validated all the key engine wiring harness connections to the ECU - AFM, TPS, ICV, Ref Sensors, O2, CTS, AC Compressor. All check out with 1 ohm or less resistance.

                    I am pending to check injector wiring, once i close the engine (valve cover). At this point I am back to the first step. I got another AFM, to try out.
                    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


                    • #55
                      Hi, Good to hear you are making some progress, back to the cylinder leak down check where is the air escaping from seems like quite high numbers you have
                      should be able to hear from the exhaust or the intake and have you checked the valve clearance are within the 10-14” range.

                      I have not done a cylinder leak check for many years so not to familiar with the figures you have so quick look on google said a good cylinder should be 5-8% leakage..

                      E30 M3 1987
                      Mini Clubman GT
                      BMW E36 323 Msport
                      Toyota Corona
                      KTM 200EXC
                      Honda CB50 (1979)

                      Comment


                      • #56
                        Originally posted by Dave @nz View Post
                        Hi, Good to hear you are making some progress, back to the cylinder leak down check where is the air escaping from seems like quite high numbers you have
                        should be able to hear from the exhaust or the intake and have you checked the valve clearance are within the 10-14” range.

                        I have not done a cylinder leak check for many years so not to familiar with the figures you have so quick look on google said a good cylinder should be 5-8% leakage..
                        I just compared these numbers to a different M3, I worked on earlier in the year. It had higher leakdown % (on a warm engine), and the car runs solid.

                        All valve clearances are in range 0.011-0.013".

                        I will redo the leakdown test, and try to identify where is air coming from. I haven't checked if the dipstick might be a cause.

                        Still pending to swap the ref sensors. Also do another fuel pressure test, this time driving.
                        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


                        • #57
                          Reference sensors are replaced. No change.

                          What I noticed, quite pronounced for the first time, is that when cold even with the AC the car revs just fine. As the engine approaches closed loop the response gets more and more sluggish. That would mean TPS, CTS and O2. I have a new CTS, swapped multiple TPS (confirmed working just fine on my S38), so the only thing pending is an O2 sensor.

                          Additionally, upon crank up (when cold) the car would usually hesitate to get to idle. Upon restart, it is fine. Sounds like the intank pump is not holding fuel level, so needs to be re-primed upon long no start. I am either going to finally swap the intank pump as well, for a unit I have, or add a check valve.

                          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


                          • #58
                            I am not sure if this will help. I was just at shop dropping parts off for my car. They had been trying to resolve a hesitation problem on a M3 for some time. It had a long list of problems when they got into it, gas, pump, filter, just disgusting. They fixed all that and would still get issues. Finally tracked it down to ground pin in the harness that had deformed and flared out. I believe he said it was to the coil or something. I won't do justice on explaining but.... Also, those leak down numbers don't seem good. Are you consuming oil. We did a leak down on mine before taking apart and it was less than 6% for all for cylinders.
                            Dan

                            88 M3
                            Black on Black

                            San Diego, CA
                            USA

                            Comment


                            • #59
                              Replaced the O2 sensor, without change.

                              Next step, is to feed all the important signals - ICV, TPS, AFM, O2 from the ECU (as they are read) into a data acquisition system, and see what I get. I will check the ground pin(s) before that, as well.
                              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


                              • #60
                                I was able to finally gather some of the important signals and plot them over, while driving.

                                To recap the symptoms - the car has a very low intake manifold pressure 10-12cmHg, and dropping when idling. It drives fine if the AC is not ON, from a stop. If the AC is ON, taking off from a stop the car is hesitating, and could die sometimes.

                                The data plots would be - AFM Input V (Up), AFM Power V (Uv), TPS WOT, TPS Idle, O2, CTS, AC ON signal. Fuel pressure was confirmed while doing all these test, rock solid at 3bar (43.5psi). The plots are attached in below. Feel free to comment. Here is a video at idle - https://youtu.be/_GCbzDsP-GY

                                First, I tested the entire harness from all the devices to the ECU plug. Everything checked out with less than 1ohm of resistance. The replacement reference sensors, did not make a difference. O2 is also replaced with a brand new piece.

                                I redid the leak down test, on a hot engine. The numbers look as following:

                                Cyl 1) 20%
                                Cyl 2) 35%
                                Cyl 3) 28-30%
                                Cyl 4) 25%

                                The air leakage would be quite pronounced testing cyl 2 (35%), when i open the dipstick tube. That would make me think that air is escaping past piston rings. I have tested S14s with higher leakdown numbers, that would performed completely differently aka better.

                                Additionally, I started tracing auxilary systems that run off of vacuum - FPR, Fuel Evap Purge, and Brake Booster. I plugged the Evap Purge, and disconnected the Brake booster without changes.

                                As smoke tests did not yield any leaks, i tried compressed air into the intake manifold (~25psi). With the brake booster disconnected, and plugged the only spot of air leak would be the oil cap. Upon holding down the oil cap down, I would not hear any other leak points. Tried a different Oil Cap too. That makes me conclude that there are no vacuum leaks.

                                I also tested with the exhaust disconnected, thinking the CAT might be restricting the flow. No difference.


                                ------------------------------------------------------------

                                Data Plots

                                Figure 1 shows the E30 at Idle. As can be seen the Uv/Up ratio has spikes of up to 18V/V. That is driven by the low vacuum in the intake, forcing the AFM door to close for short bursts of time. The orange TPS idle signal indicates, when the throttle is slightly blipped. The Throttle here never reaches WOT, because I have a Carbtune gauge hooked up to the ITB.

                                Figure 2 demonstrates the driving condition. I am not showing TPS WOT signal, as I never really got to WOT, but the TPS has confirmed switching functionality at 80% to WOT. The Gray line is when the AC kicks on.

                                Figure 3, is the same data plot as Figure 2, with O2 V on the secondary showing it swinging from 0.8 down to 0.15 V.
                                Current: '95 E34 540i/6 Hellrot/Pergament | '88 E28 ///M5 Schwarz/Natur | '85 E23 745i Diamantschwarz/Buffalo
                                Past: '83 E28 533i/5 Schwarz/Schwarz

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