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S14 hesitation at WOT

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  • S14 hesitation at WOT

    Long time E28 M5 owner, jumped over at the S14 side for a short while now, while helping a friend get his car baselined.

    I have been fighting this E30 M3 for while now, and can't seem to find the problem. Sort of. The car ran fine before valve adjustment, cap/rotor, sparks and new wires. This is when I got it, with the issue below. None of the original components are available to swap back over.

    At WOT the engine will hesitate and take a good 2-3 seconds to rev. Upon load, taking off from a stop it will even die. If i do partial throttle, the engine is accelerates fine.

    So far, I have replaced the ICV hoses #16, 17 as they had signs of deterioration https://www.realoem.com/bmw/enUS/sho...diagId=13_0285

    Also cleaned the ICV.

    JB Welded the elbow at the throttle bodies. The elbow at the intake is fine. Smoked the engine with a fog machine, no clear visual leaks. I haven't checked the brake booster elbow, but might do that next.

    ITB balance and sync, valve adjustment (redone, no issues found), fresh o-rings on the ITBs and the adjustment screws. Two different 028 AFMs tested (from a good known car). Adjusted the orignal AFM to the car, to read roughly 0.5V at the 02 sensor.
    a
    Spark plugs are NGK, and bremi wires. Idle set at 850rpm with bridged TPS. It goes up to 910-20 rpm when TPS reconnected.

    Different TPS tested too (verified good as well).

    At one point, I thought I nailed the problem as a vacuum leak at the valve cover. But today after swapping from a good set of Bosch X5DC back to the NGK, and redoing the smoke test, I ended up back to square one. Just replaced the airbox to intake elbow. Now i can't get it to run normal again.

    I get about 10-12cmHg when reading vacuum at the ITBs. So i attribute it to vacuum leak still, but why it changed so abruptly from being OK back to hesitation, I am not sure.

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

  • #2
    Hi,
    Some times the elbow hose between the AFM and engine collapses when quickly opened to full throttle, this can happen if the hose is new and soft and the air filter is not new condition.

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

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    • #3
      Originally posted by Dave @nz View Post
      Hi,
      Some times the elbow hose between the AFM and engine collapses when quickly opened to full throttle, this can happen if the hose is new and soft and the air filter is not new condition.
      This happened to me but only under WOT at high RPM. I installed a home made coil to fit in the elbow and worked beautifully.
      sigpic 95 M3 & 88 M3

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      • #4
        That is an interesting theory. The air filter is new too. And it hesitates even when just raving to WOT in my driveway/garage.

        Forgot to add - fuel pressure was also in good, verified.
        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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        • #5
          Just to throw it out there i had a new boot installed and didn't get this starvation due to the boot folding in on itself until a little while after. maybe a month I'de say. But maybe i was not running the car hard in that time. Cant say for sure
          sigpic 95 M3 & 88 M3

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          • #6
            A vacuum leak will not cause issues at WOT. The engine generates no vacuum at WOT as the restriction, the throttle butterflies, are open. WOT throttle issues are normally high tension voltage related as the voltage required to jump the spark gap in the high pressure cylinder is higher than the voltage required to find earth.

            Try revving the car in the dark and look for sparks in the plug lead holder. Listen also for the tell tale cracking of a spark going to earth.

            Are the cap and arm matched to each other? There are two types of each and they only work in matched pairs.
            Sport Evo No.47

            My Sport Evo Restoration

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            • #7
              did you swap out your cluster? The cartridge might of been swapped out and replaced with another then m3 one. PN 62111381699

              #11
              https://www.realoem.com/bmw/enUS/sho...diagId=62_0064

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              • #8
                Originally posted by e30m3black View Post
                did you swap out your cluster? The cartridge might of been swapped out and replaced with another then m3 one. PN 62111381699

                #11
                https://www.realoem.com/bmw/enUS/sho...diagId=62_0064
                Interesting point. But no it has not been touched.
                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


                • #9
                  Originally posted by stevesingo View Post
                  A vacuum leak will not cause issues at WOT. The engine generates no vacuum at WOT as the restriction, the throttle butterflies, are open. WOT throttle issues are normally high tension voltage related as the voltage required to jump the spark gap in the high pressure cylinder is higher than the voltage required to find earth.

                  Try revving the car in the dark and look for sparks in the plug lead holder. Listen also for the tell tale cracking of a spark going to earth.

                  Are the cap and arm matched to each other? There are two types of each and they only work in matched pairs.
                  That's a great point, on vacuum leak at WOT.

                  I will check the cap and arm. They were installed brand new out of the box, by owner.

                  Since I last posted, I found the CTS to be acting up. If unplugged, when car is hot, it won't rev up. I got 100 ohm reading. I let it cool down for 20 min, measured resistance at 360 ohm. Fired the car up, and it revved to WOT fine! I did test the CTS originally, and it did what it was supposed to. The replacement CTS is in the mail, and should be here tomorrow.

                  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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                  • #10
                    Are you sure it's wot or on the way towards wot? Thinking about tps or afm sweeper arm or door...
                    2 seconds though... Did you rev in engine bay and stare at intake elbow?

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                    • #11
                      How is the O2 sensor?

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                      • #12
                        At WOT, the WOT switch in the TPS is activated. This puts the ECU in to open loop control and the O2 sensor reading is disregarded. Likewise the AFM.

                        Is the WOT switch activating?
                        Sport Evo No.47

                        My Sport Evo Restoration

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                        • #13
                          This ^^

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                          • #14
                            Swapped the CTS with a brand new one. When disconnected, the car will still die.

                            proctor750 stevesingo The TPS is actually out of my E28 M5, verified operating properly. I have it set to click just off idle. The original TPS out of this M3 is now in my M5, and works just fine. I haven't really stared at the elbow while revving it. But it used to do this, with the old elbow which was hard as a rock, but had cracks.

                            I will do a check on the WOT switch at full open of the linkage.

                            e30m3black i believe 02 is fine-ish. I can get it to bounce around 0.5V when hot. I bench tested the AFM (it is a 028) no dead spots, i took it apart and cleaned the tracks with a pencil eraser. I tried a good known 028 AFM as well, there was no difference. If anyone has a 028 AFM for sale, i would consider buying for a spare.

                            Found this thread last night looking for WOT conditions - https://s14net.vbulletin.net/forum/s...pm-wot-stutter The OP had the exact same problem. Upon disconnecting the TPS, naturally it drives, as there is no WOT.


                            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


                            • #15
                              Just visualize what the situation is currently, here is a video as is - https://youtu.be/sOmpp2TextM

                              Here are a few other tests:

                              Fuel Pressure, with hesitation at WOT as seen - https://youtu.be/Z-dWMpYH3uI

                              For comparison with above video, this video is after I had it FIXED - https://youtu.be/UUXFHcATlU0 - all i did is redo valve adjustment, which was fine and reseal the valve cover a little better. Running a different AFM. After that I swapped AFM (back to original), and it was still fine. Then redid spark plugs from X5DC back to the NGK and then went back to square 1. Since then I have went back to the BOSCH, and OEM spark plug wires. No difference.

                              O2 Adjustment, as it was FIXED - https://youtu.be/eqmbLKyq3jo

                              Just swapped TPS, had a different 319 laying around. What I removed at WOT would read 1.5 ohms. At rest 0.5 ohms. Installed at WOT 23 ohms (!) and at rest 0.5ohms. No change.


                              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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