Announcement

Collapse
No announcement yet.

S14 hesitation at WOT

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

  • #16
    Have you tried swapping both the main relay and fuel pump relay with known good / fresh units?
    Either one of those starting to fail can cause the car to falter then "catch".
    I've seen a failing intermittent main relay befuddle two different BMW service departments on a friends car until I found it.

    Also I did not see mention of trying the flywheel sensors.
    I have seen flywheel sensors fail manifesting themselves almost as a rev limiter. Not exactly how you are describing, but they are worth a try.

    To me this sounds like a something failing or about to fail problem, not a simple tune up issue. Something that makes the car "go" is starting to fail, or the wiring going to it is intermittent or starting to fail. I dont think its anything related to the traditional "tune up" parts.
    Thats where I would be looking.
    jimmy p.
    87 E30 M3 Prodrive British Touring Car
    88 E30 M3 Zinnoberot - Street
    88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
    92 E30 M Technic Cabrio - S14 POWERED!
    98 318Ti M44, Base - Morea Green
    04 Ford F350 - V10

    Comment


    • BBS16
      BBS16 commented
      Editing a comment
      As Jimmy posted its worth checking the wiring for continuity back from the CTS and the TPS to the ECU? With our wiring being however old it is, corrosion may have set in where its crimped into the connectors or may be hanging on for dear life on a few strands somewhere else?

  • #17
    BBS16 and jimmy p. yeah next on the list are ground straps, and reference sensors.

    Drove the car, yesterday at speed. Let's put it this way - at 80mph in 5th (3000rpm) with the pedal welded to the floor there absolutely 0 movement of the rev counter! In 4th gear it will feel like a misfire in higher rpm.
    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


    • #18
      Just a wild guess, but by any chance did you remove the pulse damper from the fuel line? I recall years ago some owners ran into unusual fuel starvation issues at high rpm after removing it.

      Comment


      • #19
        Have you removed the fuel filter and drained it incase it is blocked up with rust, next thing I would do is run some temporary wires from a 12v battery to each of the pumps (I think possibly yours is early M3 dual pump) and run them one at a time incase possibly the main pump has failed and it is running on the lift pump in the tank or vice versa.


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

        Comment


        • #20
          plug in that diagnostic tool =)

          Comment


          • #21
            Have you swapped DME...

            Comment


            • #22
              proctor750 yes, tried with different DME. And put this DME in another M3. No change.

              Dave @nz the fuel pumps are good. I have a pressure reading at the rail. There is no rust, and a new filter has been installed.

              Chris W I need to see if the dampner is still there, i can't remember. I recall reading about that too.
              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


              • #23
                With WOT issue I was also thinking a collapsed air boot (already checked) or fueling issue (also checked). Did you say it ran fine immediately before? In that case definitely look at anything changed (but believe you said the cap and rotor have been inspected and a known good wire loom tested).

                With the lag after throttle application in the videos I wonder if it's a flow issue. What about a clogged cat? It's easy enough to unbolt the exhaust at the header and you'd only need to replace the gaskets.

                Comment


                • #24
                  Originally posted by ethirtym View Post
                  With WOT issue I was also thinking a collapsed air boot (already checked) or fueling issue (also checked). Did you say it ran fine immediately before? In that case definitely look at anything changed (but believe you said the cap and rotor have been inspected and a known good wire loom tested).

                  With the lag after throttle application in the videos I wonder if it's a flow issue. What about a clogged cat? It's easy enough to unbolt the exhaust at the header and you'd only need to replace the gaskets.
                  I was just about to say - snagged an exhaust from junkyard for an E36 m3 and of course it had a blown headgasket so cats were clogged and similar symptoms BUT there was obvious power decrease across the board. Used a pressure gauge to find the clog.

                  Weren't you waiting for something in the mail to swap in?

                  Does power delivery feel normal at part throttle? It's only WOT that it falls on its face? What if you very slowly open the throttle (i.e rolling in 3rd) until you reach WOT? Will it catch you or let you get into power?

                  Comment


                  • #25
                    Right now, I am working on a different E30 M3. I will resume on this car by end of this week.

                    Yes, CAT came to mind too.

                    The power delivery is fine at part throttle, and up to WOT after up until I reach 60mph. After that it plateaus. In 5th gear at 80mph there is absolutely no power.

                    I have an Innovate LC-1 that I will install to monitor stoich, check relays, check ref sensors, and CAT. In no specific order.

                    Thanks for all the continuous input, guys.
                    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


                    • #26
                      Spark plug gap ok? Are they the correct type (Resistor VS non-resistor)? Do the spark plug wires have the correct resistance?
                      Dizzy finger correct R too?
                      Condition of ignition coil?
                      Does it rev to the red line with the car put of gear? If yes, I suspect a flow problem, be it air, fuel or exhaust not an ignition problem. Still it could be that the spark is blown out a higher load as in wot while driving.

                      Comment


                      • #27
                        Would an intake manifold gasket leak cause this problem?

                        Comment


                        • #28
                          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 88hennaM3 suggests. I have replaced all hoses to ICV. The oilseparator one look good. So the gaskets are the only ones left.
                          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


                          • #29
                            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 88hennaM3 suggests. I have replaced all hoses to ICV. The oilseparator one look good. So the gaskets are the only ones left.
                            Good to hear the different catalytic convertor made a big difference. Make sure you address the issues that led to a clogged cat. You're saying the CTS sensor has an issue? I believe a faulty CTS could cause a rich condition which would clog a CC. Did you make any new videos of it running? Intake leaks could cause a lean condition. If your rubber blocks haven't been replaced in long time it would be worth doing - I replaced mine at just over 100k miles and they had lost flexibility. The stock plenum is heavy which I believe opens a small gap at their top edges.

                            Comment


                            • #30
                              The throttle response with ITBs of course should be near instant. You were manually opening the butterflies in your video so there should be plenty of air available instantly. As you say the car accelerates to 80+ mph pretty strongly so I'd guess spark and timing are pretty good. I still think there's a possible or probable fueling issue: fuel pressure, poor atomization, dirty, malfunctioning or clogged injectors.

                              Check out this video and note at 1:10 and 1:35 symptoms of a weak fuel pump or dirty filter. A weak fuel pump might be to blame if pressure drops more than 1 psi when opening throttle
                              https://www.youtube.com/watch?v=peh7-pFycyc

                              In your video it looks like your psi drops from about 44 or 45psi to nearly 40
                              Fuel Pressure, with hesitation at WOT as seen - https://youtu.be/Z-dWMpYH3uI



                              Comment

                              Working...
                              X