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Tachometer not working

Discussion in 'Subaru Sambar' started by Reese Allen, Oct 31, 2019.

  1. Reese Allen

    Reese Allen Member

    Here's my code, if anyone happens to be a programmer/Arduino guy:

    edit: My RPM calculation should have a 1000 instead of the variable delayTime.
    Code:
    float value = 0;
    float pulseCount = 0;
    int rpm;
    int oldtime = 0;
    int time;
    int delayTime = 1000 ; // in ms
    const int signalPin = 19 ;
    
    void isr() //interrupt service routine
    {
      pulseCount++;
      //Serial.print(rev) ;
      //Serial.println();
    }
    
    void setup()
    {
      Serial.begin(9600) ;
      pinMode(signalPin, INPUT_PULLUP);
      attachInterrupt(digitalPinToInterrupt(signalPin), isr, RISING) ;  //attaching the interrupt
    }
    
    void loop()
    {
    
      delay(delayTime);
      detachInterrupt(digitalPinToInterrupt(signalPin));           //detaches the interrupt
      time = millis() - oldtime;    //finds the time
      rpm = ((pulseCount / time) * 60 * delayTime) / 8; //calculates rpm
      oldtime = millis();           //saves the current time
    
      Serial.print("RPM: ") ;
      Serial.println(rpm) ;
      Serial.print("Pulse count: ") ;
      Serial.println(pulseCount) ;
      Serial.print("Time interval: ") ;
      Serial.println(time) ;
      Serial.println();
    
      pulseCount = 0;
    
      attachInterrupt(digitalPinToInterrupt(signalPin), isr, RISING);
    
    }
     
    Last edited: Mar 29, 2020
  2. Reese Allen

    Reese Allen Member

  3. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    With regard to getting too many signals: Some of the ignition control boxes send multiple pulses throughout the dwell cycle. So, you don’t have a steady single pulse, but a variable number based on the rpm.

    You might be better off with a crank sensor, pick up sensor, so you know exactly how many pulses.
     
  4. rkrenicki

    rkrenicki Active Member

    So, I re read this thread a bit. You have a factory tach, so just to double check.. you have a supercharged van, correct?

    If so, the tach signal at the cluster has nothing to do with the ECU, “points”, or ground coupling. It is a dedicated wire straight off the coil just for the tachometer signal (as I said original way back at the start of the thread)

    I have the Japanese service manuals and wiring diagrams.. I also retrofitted a tach cluster into my supercharged truck, and I had to run said wire to make it function.

    I can take photos of the connection at the coil and the diagrams tomorrow and post them here. I can also measure what I am seeing with my oscilloscope to give you a better idea of what it is doing for me.
     
  5. rkrenicki

    rkrenicki Active Member

    I found the requisite pages of the wiring diagram, added some text and highlighted the wire in question. As you can see, it does not go anywhere else but to A16 on the cluster and pin 2 of the coil.
    Screen Shot 2020-03-31 at 12.18.33 PM.png Screen Shot 2020-03-31 at 12.19.20 PM.png

    I went and snapped a photo of the wire on my trucks coil. I added this wire, so it looks a little different, but it should still be yellow on yours. I also added a photo of the reading at warm idle both at the cluster and on my oscilloscope. I get a reading of around 280-290hz at the scope, but the waveform is very dirty, so I am not entirely sure how accurate the readout is. I took this measurement right at the coil itself since I did not want to pull my dash apart.
    20200331_155623620_iOS.jpg 20200331_154931948_iOS.jpg 20200331_155543960_iOS.jpg
     
  6. Reese Allen

    Reese Allen Member

    Thanks for the info. Yes, it's supercharged.

    My aftermarket tach showed up early. I set it to 4-cylinder mode and then attached it to the VCC, GND, and tach signal conductors in the dash. It reads the same as my homebrew tach. Idling in the 1500~2000 range, even when warm, and goes up to around 6000 when I rev it.

    If this signal is reliable, and I'm starting to think it is, my engine is idling at about 600~1000 RPM higher than what everyone else considers normal. I get garbage fuel economy (23 MPG if I'm lucky) despite having done all of the maintenance and tune-up items I could think of since buying it last year, and mostly driving it on the highway, so it wouldn't surprise me at all if something is f'ed up unrelated to the tach causing it to idle high.
     
  7. rkrenicki

    rkrenicki Active Member

    23mpg is not really terribly low.. I average a little over 11km/l which works out to just under 26mpg with a good amount of highway driving in my truck. The problem is that these sambars are as aerodynamic as a brick and are not geared for our highways. So, while a Vivio RX-R can get high 30s, low 40s MPG.. our poor Sambars will get more like 25.

    That said, a high idle could be a sign of a vacuum leak. I also found that both of the rubber intake couplers for the supercharger on mine were dried up and cracked. I ended up replacing them with some silicone hose couplers way back when I did my rebuild. The are 48mm (1 7/8") inner diameter.
     
  8. Reese Allen

    Reese Allen Member

    I got my hands on a timing light. I went and hooked it up, clamped the inductive thing over a plug wire.

    I started the van in my driveway and let it warm up for a good 15 minutes. Much longer than I had been letting it run before. Revved it a few times, let it warm up another 5-10 min. The idle RPM takes quite a while to get down to the true idle speed, which turns out to be about 800-900. Awesome. (during this time I also checked for vacuum leaks and was unable to find any.)

    With my new aftermarket tach hooked to the wire in the dash, it's displaying the same RPM as the timing light within 100 RPM. So that signal wire is definitely trustworthy, and I guess it just gets ~8 pulses per rev instead of the 2 I was expecting. But I don't want to mount that tach in my van, I want to mount it in my Chevy.

    Next step is to finish building my new Arduino-based tach module and get it mounted up. Then I will calibrate it using the timing light. That part of the project is going really well so far, and if I don't get it finished tonight or tomorrow it'll definitely happen over the weekend.
     
  9. Ohkei Dohkei

    Ohkei Dohkei Active Member

    Good news. Yes, high idle is pretty high, but it should go down when it warms up. It sounds like yours is operating properly!
     
  10. banzairx7

    banzairx7 Active Member

    My idle doesn't drop til it's at basically full temperature. Yours taking awhile to come down sounds right.

    My fuel mileage is also abysmal. I'm guessing 20mpg. I'm attributing that to the fact the air fuel ratio is in the mid to low tens if you're on boost at all. It should be high 12's to low 13's. Yours is probably in the same ball park. The brick like shape doesn't help either.
     
  11. Reese Allen

    Reese Allen Member

    Ran into Arduino issues that prevented me from finishing the job this weekend. I have the mounting all figured out and fabbed up and it turned out great. Yesterday's problem was that the first Arduino I bought was a Nano 33 which can't output the 5 V I need to power the servo. I found some knock-off regular Nanos on Amazon with same-day shipping so I got some of those last night. Today I learn that the knock-offs apparently can't tolerate the 15+ VDC that the Sambar often generates. So I'm putting it all back together today and will retrofit with a genuine Nano when I can get my hands on one.
     
  12. Reese Allen

    Reese Allen Member

    Here's a pic. Still need to figure out how to attach the needle to the servo nicely. The little white arm the servo comes with doesn't fit through the front panel hole. Might have to shell out for a custom stepped pin, I think I could get one on Misumi. Or I might just hot-glue it...
     

    Attached Files:

  13. Reese Allen

    Reese Allen Member

    Replaced knock-off with genuine Arduino, doesn't work at all. I'm about ready to call that rabbit hole a dead end. Either I shell out $350 for a replacement tach board, if it's even available, or shoehorn an aftermarket tach into the dash. Both options suck.
     
  14. Ohkei Dohkei

    Ohkei Dohkei Active Member

    It was worth a try. I've been trying to learn a little about those things for a project I'm working on. They are really cool.
     
  15. rkrenicki

    rkrenicki Active Member

    You just need one of the stock tachometer clusters? They crop up from time to time for less than $100.
     
  16. banzairx7

    banzairx7 Active Member

  17. Reese Allen

    Reese Allen Member

    Seems like a good option. Other than this board, is there a good place to look for them? I rarely get any good hits on any actual car parts when I search buyee/Yahoo.
     
  18. Reese Allen

    Reese Allen Member

    Really cool, but relying on GPS for speed is kind of hokey. I see why they did it though.

    I have Android head units in three of my vehicles and I can tell you the GPS-calculated speed isn't very dependable. It's fine when you're cruising on the freeway but on surface streets it fluctuates quite a bit. And sometimes it just can't get a satellite signal at all for minutes at a time. Could be more of an Android problem than a GPS problem though.
     
  19. banzairx7

    banzairx7 Active Member

  20. rkrenicki

    rkrenicki Active Member

  21. rkrenicki

    rkrenicki Active Member

  22. Reese Allen

    Reese Allen Member

    Awesome! I tried to bid on it but it just keeps going up, now at 9750 JPY. I'll try to snipe it tomorrow, I guess. How much is this really worth to me... hmm...
     
  23. rkrenicki

    rkrenicki Active Member

    I am surprised it is that high. The last two that I bought were around 5000 yen.
     
  24. rkrenicki

    rkrenicki Active Member

    Holy.. 19,500 yen? That is insane.

    I get that it was modified for 4WD display and had the terminals marked.. but that is a crazy price.
     
  25. Reese Allen

    Reese Allen Member

    Yeah, too rich for my blood. I can wait.
     
  26. Reese Allen

    Reese Allen Member

  27. rkrenicki

    rkrenicki Active Member

    Yep, the only difference is the little circuit board for the gear indicator. Did you end up buying it?
     
  28. Reese Allen

    Reese Allen Member

    I did. Almost $100. Now I get to find out how long the Buyee process takes...
     
  29. Reese Allen

    Reese Allen Member

    The answer is almost exactly two months. It's here. I've started taking apart the new cluster but pulling the cluster out of the van isn't gonna happen tonight. Fingers crossed that the tach board is functional.

    Strangely, I noticed on this cluster, which came out of a vehicle with an automatic, there is a "clutch temp" warning light. My manual transmission van has no such light. I'm struggling to understand why Subaru would add a gear position indicator to the right side of the cluster for just the automatics, but would keep the clutch temp warning light on both clusters. Oh well. I'm just in it for the tach board.
     
  30. Koffer

    Koffer Active Member

    The clutch temp light is for us automatics . It’s when the electronic Torque converter (powder clutch) starts to slip and overheat or in my case it let the magic out of it and starts to blink or stay on as the transmission controller brain box says the voltage/amps aren’t correct for load/rpm etc . If it’s not dickered you let it cool down and go on your merry way could be the brushes Are worn ( cheap easy) oil coated ( cheap but not easy) or my option (Not cheap or easy) 78DB4691-6B66-403F-821E-34AB9BA21ED4.jpeg
    you end up replacing a $700 part like “this guy” :(

    hopefully you’ll have it working in no time with the new to you one . Dashes are easy to pull and since you have had yours out a few times It will take you longer to dig the tools out
     
    Last edited: Jul 6, 2020
    Reese Allen likes this.

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