Page 6 of 6

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Feb 13, 2020 2:21 pm
by AndreyB
But even with not eBay coils I have crank signal disappearing if coils are hooked up :(

Here you can compare second line signal with both coils disconnected VS one coil connected.

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Feb 13, 2020 2:31 pm
by puff
hm. shall I try cranking my oldrusty rover without a coil attached?
do you think it's just affecting the usb connection, or the whole thing?

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Feb 13, 2020 2:33 pm
by puff
one more thing, I've heard that installing a large capacitor across the coil's power lines help (although I don't understand why it should help)

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Feb 13, 2020 2:51 pm
by kb1gtt
Yeah, it's likely a huge inrush, causing the GND voltage to spike. The huge cap on the supply simply provides allot of HF energy locally, so you don't have that energy on the MCU GND.

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Fri Feb 14, 2020 4:02 am
by AndreyB
After 24 hours of head banging I've noticed that cranking RPM without coils was 480 RPM. 480 RPM is not the right cranking RPM of my car, it should be 240 RPM...

Now I am thinking that there were multiple issues introduced at different points in time - loss of GND during the catastrophic event, bad replacement coil was not helping and on top of that wrongly "refactored" VVT or trigger code has messed up engine cycle :(

Test mule now starts reliably on MRE 0.3 - if 2019 Xmas firmware is used AND there is a jumper cable between engine block and battery.

Also note how on this picture VVT fronts are inverted comparing with 2019-10-21_rpm_1102_Frankenso_MAX9926_5K_pull_ups.png in first post of this thread.

I will go have some cognac.

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Mar 26, 2020 4:03 am
by AndreyB
NB2 miata has MAF as primary load sensor, but it also has "EGR boost sensor". Could this EGR boost sensor be used as load sensor?

Looks like there is a solenoid between this EGR boost sensor and intake? Not sure.

See also https://forum.miata.net/vb/showthread.php?t=590218

PS: and second question: stock MAF reports +12 analog voltage does it? What would be a good voltage divider value to convert it into 5v signal?

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Mar 26, 2020 1:25 pm
by stefanst
The NB2 does have a "boost sensor". NB1 has it as well, as far as I know. I don't remember how the air-side of this sensor is connected though.
If I understand correctly, It is used to ensure that the EGR solenoid is opening correctly and exhaust gas makes it into the intake. The assumption is that when the EGR valve opens we get an increase in MAP. So, in theory, this sensor is a pressure sensor and should cover at least a good part of the operating range of the engine. I do remember somebody who wanted to put an aftermarket ECU in his car, but couldn't use any additional sensors due to class restrictions, planning to use that sensor as an ECU MAP sensor. I don't think we ever had any published result.

Suggestion: Run the engine at different loads and measure the signal. If it's a simple voltage signal, it shouldn't take too long.

Re: red 2003 VVT test mule Miata NB2 #27

Posted: Thu Mar 26, 2020 2:33 pm
by scramblr
My undersanding is the same.
I believe the "EGR boost sensors" is ultimately a simple pressure sensor, that most likely limits out at 1 bar (atmosphere).
It should be reading the manifold pressure like any other MAP sensor. It just isn't used as the primary load sensor with the stock controller.