[rusEfi] Miata NA 1996, 1.8L stock (#7)

[tomiata]

I dug through my junk box and found a few power resistors I could combine to get close. I have to go out of town but will try it in a few days.

[AndreyB]

Did I say that you are helping us a LOT? Because all this helps a lot.

[tomiata]

I got a set of resistors that will handle about 4 watts at 34 ohms and put that in series with the idle control. Here is the picture a shot of the scope with that:

IMG_20141014_180720.jpg (221.21 KiB) Viewed 22355 times

Edit: Settings are the same as the earlier post, 10x probe, 10v per div, 0 is at the 2nd line from bottom, 2ms per div. Trace is about 22v p-p. Measured at the ecu pin, resistors are between this point and the INJ7 low active pin. (But, I think this is wired wrong, now that I think about it.)

The idle solenoid buzz is gone. I can start with the engine pre-warmed ok, but I could not get it idle after trying a few values for set_idle_pwm. It will run smoothly above 1100 rpm with some throttle help, but dies under 900. And while cranking, timing may not be what it should be, it struggles to come to life. What options are there for adjusting crank timing and idle rpm?

[kb1gtt]

Hmmm, 1V DC and about 2Vp-p. Is that measuring the ECU pin, or is that measuring after the series resistors? Is that 12V and 10V, where is the GND level in that picture? I also see the cycle is about 8mS while the OEM was closer to 4mS.

I wonder why the OEM was all jagged, and this is more like I would expect the signal to look. Perhaps the OEM was PWMing the signal at a higher frequency. Or perhaps they have a snubbing capacitor.

[AndreyB]

New command:
set_idle_solenoid_freq X
Where X is the frequency we want for IAC solenoid. You would need to writeconfig and reset the firmware for the change to be applied. I hope to make this adjustable without IAC reboot one day, but for now being able to control it is already a tiny step
Miata default is 160Hz

[tomiata]

Sorry, I should have described the scope settings. I edited the post above.

But oops, now I think I wired this wrong.

It looks like

Code: Select all

              IAC        34 Ohm               
12 v -----+--LLLL---------rrrrr---+----INJ7
          |                       |
          +--------|<|------------+
                   1N4002

The diode should be just across the coil, right?

[kb1gtt]

You can try it this way, and you'll probably see a more flat signal, and more heat dissipated by the diode, so that diode might get hot. I'm still a trying to figure out why it appears to be going to 0V. I'm expecting that it should go from 12V to about 8V not 12V to 0V. I expect when the MOSFET is driving, it's a voltage divider across the solenoid and series resistor. The resistor should have a voltage drop.

[tomiata]

After moving the diode to be only across the IAC coil, the trace is closer to what the oem ecu. After setting set_idle_solenoid_freq 300 and set_idle_pwm 350:

IMG_20141016_193308.jpg (125.26 KiB) Viewed 22321 times

I guess it needs a few more ohms on the power resistors.

And here is a shot from the oem ecu to compare.

IMG_20141016_192147.jpg (128.84 KiB) Viewed 22321 times

(Same scope settings,10v per div, 2ms per div, 0 line is 2nd from the bottom.)

[kb1gtt]

QUCS would allow you to simulate that circuit which is safer than the real world. I've been trying to do that but time equals blah lately

[kb1gtt]

I know this resistor diode thing isn't "correct" but it's a start. If we are to try this in a way that is a bit more reproducible, we could use this resistor http://octopart.com/ac05000005009jac00-vishay+bccomponents-12635801 with this diode http://octopart.com/1n4007-mcc-10332445

It appears the OEM is dithering the solenoid with two different currents. This helps prevent "sticktion" Basically if you keep the valve moving slightly, the mechanical parts will be in kinetic friction instead of static friction. Dynamic friction is much more consistent as you don't have to overcome that peak before the valve moves. Keeping the friction constant helps control the valve, as you don't have to bump up over a pressure spike to get the valve moving. Here's a picture of static friction vs kinetic friction.

[AndreyB]

Status update: talked to Tom yesterday. It looks like we are NOT controlling the IAC - whatever values are used make no difference to the way the car runs. No idling without throttle pedal.

Is the resistor in series with IAC is a voltage divider, does not it mean that from the IAC point of view it is only getting say 8 volts, and the 4 volts are on the resistor? Not that we PWM between 4 and 12 volts, but we PWM from 0 and 8 volts. Do I understand this right?

Anyway some info on this in IAC section of http://www.diyautotune.com/tech_articles/how_to_megasquirt_your_mazda_miata.htm

[DaWaN]

I find the waveform from the OEM ECU quite weird: it is very close to 100% duty cycle on 12V. Is this waveform captured during warm-up?
Also: what is the reference here? I guess the idle valve is hardwired to 12V on one side ?

As I have a Miata engine in the shed I can have a look at this as well, but I have the '99-'00 NB engine. As far as I know the Idle valve from this engine is identical to the NA '94-'98 engine.
MS guys seem to run these valves with reasonable high PWM settings (around 350Hz) and a normal low-side PWM output with a freewheeling diode.

[AndreyB]

I guess the idle valve is hardwired to 12V on one side ?

Yes according to http://rusefi.com/wiki/images/5/5e/1996_miata_1.8_1.png @ http://rusefi.com/wiki/index.php?title=Vehicle:Mazda_Miata_1996

[puff]

10000/62≈161Hz

[AndreyB]

[video][/video]

that's with a diode which does make a major difference in the buzz. Also a pic from http://www.suregripcontrols.com/install_suppress.htm

[AndreyB]

this time I was able to get it to idle for a short time, maybe a minute, it was not stable. But changing the IAC pwm did have an affect.

This was with only the diode across the coil and I shorted out the power resistors to effectively remove them from the circuit.

What set_idle_pwm value got you a minute of idle? What was the idle RPM? When I was playing with it my IAC has allowed me to set idle pretty high, I want to say at least 1400 RPM if not higher.

Also there is an opinion that by playing with timing you can adjust idle by about 300 RPM.

By the way there were some changes to rusefi.ini project file - some dialogs were rearranged & hopefully it's a bit more useable now.

[tomiata]

I had set_idle_pwm to 600, it was running very rough around 950 to 1000 rpm. I did not let it run very long. This was warmed more than I usually do. Here is a screen shot of gauges:

Screenshot_2014-10-21-11-28-05.png (1012.54 KiB) Viewed 21851 times

Gauges are upper left: Timing
upper right: Coolant temp.
Lower middle: MAF

It first started idling at around 1200 rpm, then settled down to under 1000, after trying a few pwm values.

I want to find good timing and fuel tables to see if that would smooth it out. If anyone has a good reference, please let me know.

Earlier question on the OEM ECU IAC signal picture, that was while warming up. I can check to see if it changes much between cold and hot.

[AndreyB]

What about higher idle_pwm values? Too many unknowns and too many variables

Have you considered http://www.14point7.com/products/slc-free? If I understand it right, for $85 you get a sensor and a controller capable of linear analog output thus we would be able to integrate it with rusEfi.

[tomiata]

What about higher idle_pwm values? Too many unknowns and too many variables

Have you considered http://www.14point7.com/products/slc-free? If I understand it right, for $85 you get a sensor and a controller capable of linear analog output thus we would be able to integrate it with rusEfi.

I tried a few values from 200 to 800 for idle_pwm in the short time it was running. It was running so rough that I didn't want to torture it further.

The SLC Free Wideband O2 sensor controller kit looks good and the price is nice. This is simpler than the waltech.com open design. No op amps. Any idea how well it works? I would rather buy this than build one from scratch.

[AndreyB]

I've got an impression that people like this brand. Not sure how limited this particular model is, they have some closed source designs for $95 I believe.

[tomiata]

I ordered a SLC B Free 4.9 with the text display. I'll give it a try.

[kb1gtt]

About IAC, take note that your fuel delivery will change significantly as you change the IAC. It changes the pressure in the manifold, which changes how much fuel flows across the injector. Granted the fuel pressure regulator should keep that reasonably consistent, but it probably doesn't do it as well as you might hope. This could make for some short term issues with dynamic reactions.

[kb1gtt]

Tracing what is perhaps 1992 ECU I find this

Code: Select all

12V --> 12ohm IAC --> pin 2W or 3Q 8.2 ohm --> diode with cathode --> GND
                                           |-> TO220 to .47 ohm --> GND. 

The TO220 could be analog controlled. However it has minimal heat sinking. So due to a lack of thermal heat sinking, I think it's driven saturated, AKA switch for PWM. So I think the IAC sol runs at a constant 12V/(12+8)= .6A, and when the PWM drives it low, it increases the current to about 1A. This does not seem to perfectly match the above http://rusefi.com/forum/download/file.php?id=888 but it's probably getting close. That capture shows it going from 12V to about 8V. I would expect that with this ECU I traced, I would see 8V going to 0V instead of 12V to 8V.

So I would like to suggest we move the diode. It currently uses the diode with the white band connected to 12V. Lets try this. Same diode, but remove from 12V. Add 8 ohm resistor to diode where 12V was connected, then connect the other side of 8 ohm to GND. Remove the 34 ohm resistor. Then change the PWM duty to 250Hz or 500Hz. I think this will make it play nice. If I'm lucky, I'll get another scope capture and it will look the same as the above noted picture.

As a recap for another thread that mentions 500Hz duty instead of 160Hz, In the above graphic, it notes the OEM ECU used a duty of a bout 4mS, so I would expect the duty to be about 250Hz.

[AndreyB]

Add 8 ohm resistor

Average through-hole resistors are 1/2W, what kind of resistor do we need in this case? 2W? 4W?

For a test I want to try four 1/2W 33 ohm in parallel.

[kb1gtt]

The OEM ECU used what appears to be a 1 watt. This seems odd to me as I would expect 12.1 ohms + 8.2 ohms = 20.3 ohms. Then 12V/20.3ohms= .59amps. Then 8.2*(.59^2)= 2.79 watts. My best guess is that they expect the ON time to be low. Basically when the transistor is active, this 8.1 ohm is not active, so a 30% duty cycle would produce under 1watt in that resistor.

[kb1gtt]

Final wiring should look like this.

Code: Select all

12V --> IAC sol --> pin 4Q / W55 --> low side drive chip --> GND
                                 |-> + Diode - (white marked) --> 8 ohm --> GND

I believe the + side of the diode and low side driver chip is already installed like this. You just need to move the - (white marked) end of the diode, adding an 8 ohm resistor and connecting it to GND instead of 12V. When you do please take a scope picture to see if it is generating 40V spikes.

This is assuming your IAC sol is the same as the one used in a 92 ECU I have traced. I guess it's possible that this 92 ECU had a different sol. So this might not work perfectly. I have 2 ECU's here that I looked at and they both seem to have the same circuit, so I think this will play nice.

[tomiata]

I made a of bundle resistors, 5 47 ohm and a 100 ohm, 1/4 watt each, it measured about 8.3 ohms, should handle about 1.5 watts.
Here is a picture of the wave form,

iac-11-20-14.jpg (251 KiB) Viewed 22450 times

The buzz is back. And the resistors got pretty hot, only tested for about 10 seconds at a time. Didn't try to start the car with this in place.

[kb1gtt]

Hmmmm, that's matching what I was expecting. I see the signal going from 0V to 5V, and spikes that are tolerable. The best I can guess is that your OEM scope traces from above, do not match the circuit in this ECU. I really feel the need to make a circuit using one of these 2amp op-amps.

[tomiata]

Update on status, I had some cold solder joints on the frankenstein board that caused some erratic behavior. Now I can start reliably on rusefi when warm, and I'm refining timing and fuel settings. I'm stumbling along with that, any references on tuning would be appreciated.

And I got a 14point7.com WB O2 sensor kit and installed it. I'm not sure of the data that it's showing yet. It has a display showing temperature and lambda values. It takes a minute for it to stabilize and produce output. After it gets going the temperature value bounces around wildly. Not sure what's the deal there. The lambda value may be correct, but I don't know to expect it to be. It varies some, but mostly stays above 1.2 up to 1.36 (max value).

I'll try to get a video uploaded to show how it sounds. After starting, there is a hum sound coming from the MAF area, I'll try to capture on a video. It might be related to the IAC pwm freq, but the sound is not coming from the IAC side of the engine. Before starting, there is no noticable sound from the IAC.

[AndreyB]

[video][/video]