Don't pull the Dyno plug for road course driving

Discussion in 'Road Course, Track, Autocross, HPDE' started by strengthrehab, May 17, 2019.

  1. strengthrehab

    strengthrehab Well-Known Member

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    Based on information I read on this forum, I decided to pull the dyno plug before heading out on track yesterday. As you can see below, I lost brakes going onto a couple of hot areas. It wasn't fun. After the 2nd "off", I replaced the plug and all went back to working fine.

    I have confirmed with a good source that pulling that plus disables ABS and causes a massive shift in brake proportioning/distribution.

    Of course I broke a rear shock mount with that off so my day was over.

     
  2. DickR

    DickR Well-Known Member

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    Your source and experience matches what Ford engineers told me as I posted above. I have no idea why it doesn't happen to many open track and autocross drivers. Maybe your source can explain. Other than limited street and autocross testing I don't pull the plug BUT I'm a slow driver these days.
     
  3. NightmareMoon

    NightmareMoon Well-Known Member

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    #3 NightmareMoon, May 17, 2019
    Last edited: May 17, 2019
    I also cant explain why I’ve been able to pull the plug without loosing ABS, but I will say it didn't look like you even attempted to brake in a straight line going into Bus Stop. I hated braking into Diamond's Edge more going CCW, but Bus Stop is not a braking zone you can take lightly.

    Regardless if your ABS was functioning in this instance, I don't think it could have saved you if it was. Right about when ABS might be kicking in, you're adding steering further reducing the available traction for braking. With that line and those inputs, it wasn't going to save you. Too much steering angle.

    Hard to say for certain from the video, but that's my 2c. I've had ABS kick in at the track and not even notice until the instructor riding shotgun mentioned something about it. Its not always easy to tell with a loud exhaust, helmet, windows down, and all that stuff going on.
     
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    strengthrehab

    strengthrehab Well-Known Member

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    I was braking in a straight line. When the car wasnt stopping, I tried to turn it. I started braking early and in a straight line because I didnt trust it. I have been to this track for literally hundreds of laps and have never, not one time, blown that brake zone.

    Here is the data trace. You can see no brakes. Through the whole brake zone.

    Look at the green line and look at the track map to see where the car was at the time.

    Thanks, though. 20190517_070304.jpg
     
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  5. NightmareMoon

    NightmareMoon Well-Known Member

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    I’m just going off whats in the video. At 1:48 I hear throttle, like you hit the gas headed into the start of the braking zone and your hands are already turned, and only turn more through the rest of the turn.

    No brakes is very different from no ABS. No ABS and you should still be able to lock up the tires. No brakes and you cant even slow down. I’ve actually had a few instances of no (or little) brakes oom demand needing to pump once to find brake pressure. Maybe you had an instances of that problem. I’m still not sure what causes it, it seems inconsistant and really gives me pause about trusting the car to stop from high speed if I can’t check the brakes before the braking zone.

    From your data it also shows no time going straight. That spot on the graph you’re shifting from cornering left to conering right (from the lateral gs), and just after the brief acceleration towards the corner (ffrom lon G). I think you had no or little brake pressure maybe. Sucks tho. I wish I could point at a specific issue with the car to fix but I’ve had little luck figuring it out on my car. I dont think I’ve seen it since I did an ABS module bleed, but I cant say for certain.
     
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    strengthrehab

    strengthrehab Well-Known Member

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    Yeah, I went out right after putting the plug back on and everything worked fine. I talked to a pro driver who helped develop these cars and an ABS engineer who both confirmed that pulling that plug disables ABS and shifts the brake distribution to the rear.

    Of course, there is also another issue of going from brake to gas, to brake reducing brake vacuum, too.

    Whatever the issue was, it wasn't fun. I should have just popped the plug back together after the first incident.
     
  7. NightmareMoon

    NightmareMoon Well-Known Member

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    Is there any fix for vacuum issues going from gas to brake at high RPM I wonder?
     
  8. ddozier

    ddozier Well-Known Member

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    I have had the loss of vac issue resulting in a hard brake pedal. With my first fix I have been able to reduce it but not completely eliminate it. I first looked at the tune in the car and there is a section of tune that is related to a manual trans that Ford is using to hang the throttle open on deceleration to aid in downshifting, Ford will hang the throttle at high RPM to hold RPMs from falling too fast, this does not allow the engine to produce as much vacuum as it could if the throttle was closed. I disabled that feature in the tune and the problem is almost completely gone. I use to be able to induce the loss of vac issue at least once a day on a track weekend, once I changed the tune I had to really overshoot the rev match to make it happen again. I have since added a secondary Vac canister and a secondary check valve. I have not had it show up again but I have not tested it by over revving a downshift to force the chance of it happening. I cant say its 100% fixed for me but I have not had the issue again.

    Dave
     
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    strengthrehab

    strengthrehab Well-Known Member

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    Where did you plumb the 2nd check valve and vacuum canister?
     
  10. ddozier

    ddozier Well-Known Member

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    The 2nd vac canister needs to go between the manifold vac out and the brake booster inlet. The canister has the 2nd check valve on its inlet.

    If you do not have a dedicated track car you will need to find a smaller vac can to make sure you have room to mount it. In my car since it is caged and does not have a heater core or air box under the dash I mounted mine under the dash just behind the brake booster and routed the lines as needed.

    Do a search for vacuum canisters on eBay or google and you will have plenty to choose from.

    Dave
     
  11. DickR

    DickR Well-Known Member

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    FYI info from the FSM: I have no clue how this translates to real life, with or without the "dyno plug" unplugged even with unmodified cars.

    Supplemental Braking Assist

    The ABS module uses the HCU and hydraulic pump motor to help bring the vehicle to a safe, controlled stop in the event of severe vacuum loss in the brake booster. The ABS module continually monitors the vacuum in the brake booster through the use of a vacuum sensor. When the vacuum sensor indicates vacuum is below a predetermined level, a DTC is set in the ABS module. The ABS module sends a message to the GWM over the HS-CAN2 to illuminate the red brake warning indicator, the GWM relays this message to the IPC over the HS-CAN3 . If a low vacuum condition occurs during a braking event or if the driver attempts to stop the vehicle with a low vacuum condition in the brake booster, the ABS module activates the hydraulic pump motor in the HCU to assist with vehicle braking.

    Electronic Brake Force Distribution (EBD)

    On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module then uses wheel speed sensor inputs to evaluate rear wheel slip. Once the rear wheel slip exceeds a predetermined threshold, the ABS module commands the HCU to close the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS module commands the HCU to open the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. A slight bump sensation may be felt in the brake pedal when EBD is active.

    If the ABS is disabled due to a DTC being present in the ABS module, EBD continues to function unless the DTC is for wheel speed sensors or the HCU . When EBD is disabled, the ABS warning indicator, the red brake warning indicator and stability-traction control indicator (sliding car icon) illuminate.
     
  12. ddozier

    ddozier Well-Known Member

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    Watch the video at .25 speed and at 1:47.573 you lost manifold vac according to the gauge on the dash. I you listen carefully you also had two very short throttle inputs just prior to going to the brake pedal or maybe while on the brakes. My guess is that loss of vac triggered your braking event not the dyno plug being disconnected. I have had similar events in the past when rev matching for a downshift and the vac signal is lost at the brake booster. I would think there may be a log of the event in the PCM or ABS module but I do not think a normal scan tool will be able to view the logs only Ford VCM. As a precaution I would look at the brake booster vac line, check valve in the booster and depending on the manifold you are running on the car I would check the vac venturi vacuum pump on the front of the intake manifold. Make sure all connections are tight and no signs of cracked hoses. Inspect the lines going to the back of the intake for the vacuum actuated modules mounted on the rear of the intake.

    Did the brake pedal go rock hard during this event?

    Dave
     
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