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Microsquirt and the LH2.4 VR sensor reading a 60-2

qwkswede

Old and Slow
300+ Club
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Mar 19, 2003
Location
Denver, CO
Microsquirt and the LH2.4 VR sensor reading 60-2 crank position sensor

I am trying to do a quick megasquirt install on my 1992 240. I bought a Microsquirt unit, version 3 they call it. It saved me lots of assembly time, and it seems to be a quality piece. But I'm having some trouble getting a clean signal from the crank speed sensor, aka VR sensor on the flywheel.

The car runs, but won't rev past 3000 rpm. At that rpm it loses sync from the sensor and I get ECU resets.

I found this article at DIY Autotune about noise specific to the 60-2.
http://www.diyautotune.com/tech_articles/vrsensor/megasquirt_vr_index.htm

So I added a 10k ohm resistor in line to the VR sensor. With this resistor installed the "rev limit" is now at 1500-2000 rpm range.

The microsquirt unit does not have adjustable potentiometers on the VR filtering circuits. I don't even know what they look like because they are sealed up in that beautiful case. So I'm at a loss here. Do I keep trying different resistor values until it works? Does anyone have a recommended resistor value that does the job?

What exactly am I doing here with the resistor? Is this simply reducing the voltage from the VR sensor across the board, or is there a ow pass/high pass filtering effect happening here because of the inductor and resistor interacting?

=================
Adding my VR sensor wiring

Microsquirt VR1(+) ===> EZK pin 23
Microsquirt VR1(-) ===> EZK pin 10
Microsquirt VR(shield) ===> EZK pin 11
 
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Something you might try is putting around a 500-1500 ohm (see what works best) resistor across the sensor signal and ground. I did that on mine to help with some of the sync losses on startup, really helped. Got that little tip from Nathan.
 
I believe you use a shut resistor instead of an inline resistor with the v3 uS, it doesn't have the same vr circuit the old stuff has
 
go into tuner studio and run the tooth logger with the car at idle. Post a pic of the bar graph it shows you.
 
This is good information so far. A good guide for Volvo 60-2 and How To Microsquirt information.

I didn't know about the internal shunt resistor. I'll have to open up the microsquirt unit and get access to that solder pad. My feeling is that this might be needed. I didn't realize that I was working with an entirely different VR sensor circuit now. The auto sensitivity adjustment is interesting.

Burstcurse. I'll snap some tooth logs tonight. I was staring at them last night, and everything looks great at idle. I didn't get a log of the sync loss at higher rpm. I'll grab that tonight for documentation purposes. I have seen this on other MS installs in the past and it was pretty obvious that I was getting sync loss from the VR sensor. So I didn't bother to log the tooth pattern. But I had no idea how to address the issue with Microsquirt. I didn't even realize you could open the case.

I'll add to the first post too, but my VR sensor wiring looks like this:

Microsquirt VR1(+) ===> EZK pin 23
Microsquirt VR1(-) ===> EZK pin 10
Microsquirt VR(shield) ===> EZK pin 11

<a href="https://picasaweb.google.com/lh/photo/XzGYSRVcKloGXtOYggAQedMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-BimK1SU_who/VPQO8lA498I/AAAAAAAAJnA/AgNiYck8hak/s800/IMAGE_1348.jpeg" height="800" width="600" /></a>
 
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http://www.useasydocs.com/theory/vr.htm

According to that document, there is a spot on the circuit board to add a shunt resistor. But they don't suggest a value to use. Does anyone have a suggested value for a shunt?

You generally use a value equivalent to the resistance of the sensor itself.

If the resistance across your sensor is 10k ohms then you'll want to use a 10k ohm shunt resistor.
 
if your sensor reads 10k ohms get a new one. they should be between less than 500 ohms when new. as they start failing you will see higher ohms until the wires break and it no longer works.
 
oh well thanks, but seriously 10K= bad sensor and also no wonder why so many problems.

just pointing this out, not that your example is a bad one. but seriously putting a resistor on a bad vr sensor would only delay the inevitable tow truck.

how about tell him get a 1k resistor because thats about what the sensor should be if used but still good condition.
 
just pointing this out,

You're not pointing out anything other than the fact that you should avoid pressing the "post" button 99.9% of the time you pound on the keyboard.

Believe it or not there are quite a few people reading this thread that run something other than the factory Volvo sensor. Different sensors from different applications have different values of resistance across the sensor and the shunt resistor is sized accordingly. Using a resistor that has a value equivalent to the resistance across the sensor is a good place to start because you can eliminate stray capacitance without overly attenuating the input to the conditioning IC on the ECU.

Whether or not the sensor is good is irrelevant, that's not the topic of this thread.
 
If the ignition capture edge was wrong, or the +/- wires were swapped somewhere, would this cause the symptoms? A composite tooth log (for detailed edges) and a std log (for loss-of-sync reason) would be great.
 
Problem Solved

This problem has been fixed for my car.

- After reading the Microsquirt VR conditioner page a few more times and getting a look at the circuit board, I realized that the shunt resistor is already in place on the circuit board. You simply bridge 2 solder pads to put the shunt resistor into the circuit, or leave them open to run without the shunt. I still don't know what the resistor value is. But it doesn't matter, the circuits auto adjust across a pretty big range, and the attenuation from the shunt resistor just moves the signal voltage down to an expected range for the conditioning circuitry. That's my non EE explanation anyway.

- Here are more details about the circuits and the piece that helped me fix the problem.
http://www.useasydocs.com/theory/vr.htm
Thanks to Linuxman51 for pointing me in the right direction. The megasquirt documentation has become difficult to search the last couple years. There is just so much of it now.

In summary, the documentation specifically points out 60-2 and other high tooth count wheels being prone to noise, partly because the VR sensor voltage can reach 100 volts or more as the rpms rise and overload the circuits.

The pictures below show how I soldered the 2 tiny tiny pads together to install the shunt. 5 minutes of work and I re-installed the unit. VOILA, it revved perfect all the way to 5000 rpm sitting in my garage. No pictures, but I also removed any inline resistors to the VR sensor. The wires are connected directly from sensor to the VR+ and VR- leads.

I would recommend this adjustment for anyone setting up microsquirt V3 to run with the Volvo VR sensor. Probably most 60-2 setups would work better with this adjustment done.


<a href="https://picasaweb.google.com/lh/photo/pgX0uPdMCGeWITlp28mSL9MTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-LSbzpf4APeM/VPa411AULUI/AAAAAAAAJno/dg268uxXyIA/s640/IMAGE_1349.jpeg" height="640" width="480" /></a>


<a href="https://picasaweb.google.com/lh/photo/lp0WPbNY6PbFrQhRCzTIudMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh4.googleusercontent.com/-6mcjIesr3aU/VPa43XoMXRI/AAAAAAAAJnw/FK9jpwfCijU/s640/IMAGE_1350.jpeg" height="640" width="480" /></a>

The parts are truly tiny. I could not see the solder bridge covering the pads with my bare eyes. Taking a picture and magnifying helped me verify the pads were soldered.
<a href="https://picasaweb.google.com/lh/photo/-zH3yao4RlNsPqymr6FWOdMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-ZGMi5Wi7s0s/VPa44bZKzUI/AAAAAAAAJn4/GjG8UGOdvmE/s640/IMAGE_1351.jpeg" height="640" width="480" /></a>

And a tooth log after the mod. this is at 2800-3000 rpm range. Exactly where the noise problem was. And now it looks quite good. The pattern looks this way no matter the rpm. The couple shorter teeth midway between the tall towers are interesing. They only appear at this 3000 rpm range. Maybe they are related to the noise and sync loss, but not causing any problems now.
<a href="https://picasaweb.google.com/lh/photo/_q4drmgt982PGfjDSeX0kNMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh4.googleusercontent.com/-dP65X0hPCLk/VPa45nlT2UI/AAAAAAAAJoA/PMfgDrUfW7o/s640/IMAGE_1352.jpeg" height="480" width="640" /></a>
 
Rock n roll. I had been considering using a hall sensor with this, but if the the stock cps works, that's great! Thanks for the update Ken.
 
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