MicroSquirt.com read only forum (Jan.15,2018)

Bruce,

The problem I'm currently having is the RPM dropping to zero during cranking. I have the VR sensor with the positive lead wired to the coax center and the negative lead wired to the shield, and the shield wire grounded to the same ground as the microsquirt.

My ignition input capture is on rising edge, and the cranking trigger is on calculated. I have played with the wiring and polarity, and the way it is currently set up is the only way I can get any sort of tach signal.

simplified wrote:Bruce,

The problem I'm currently having is the RPM dropping to zero during cranking. I have the VR sensor with the positive lead wired to the coax center and the negative lead wired to the shield, and the shield wire grounded to the same ground as the microsquirt.

My ignition input capture is on rising edge, and the cranking trigger is on calculated. I have played with the wiring and polarity, and the way it is currently set up is the only way I can get any sort of tach signal.

I assume you are using the wheel decode mode - is this just crank, or crank+cam input?

OK - if you perform a datalog during cranking and then open in Excel, there is a "dt" column - this is the delta time between input tach events, in microseconds. Take a small snapshot where the RPM dips to zero - is there a correlation in delta_T?

- Bruce

I am having the dreaded lost cranking rpm right now too, at least intermittently. Really annoying.

I am starting my own post so as to prevent any confusion about who's config belongs to whom.

I'll help as I can,
Geoff

Bruce,

I am using the dual spark option with just a single M-N crank wheel signal input.

Yes, there is a correlation. The delta_T column drops to zero when the rpm column drops to zero.

-Sean

simplified wrote:Bruce,

I am using the dual spark option with just a single M-N crank wheel signal input.

Yes, there is a correlation. The delta_T column drops to zero when the rpm column drops to zero.

-Sean

How many teeth - is the 36 with one missing, etc. (just so I know exactly).

A question - when you change the VR polarity, is there any improvement/detriment to the RPM going to zero?

Also, can you unhook the injectors, ignition, and sensors (tie the coolant, iat and tps to sensor ground to let them default to a known value) so that the only thing going to the engine is the VR sensor, and the PC connection with MT. Then crank and see if there is any difference (again switch polarity) - can you get a steady RPM. By doing this any ground issue due to ignition and injectors.

If you still get noise, the last thing I would try is to have the same setup as above, this time go one step further and run the uS on a 9-volt battery or other battery source. If you now get steady RPM then this leads to noise from the starter motor (I just fixed a setup with this exact issue). By doing this in stages we can identify the offending noise source and eliminate.

You should be able to get a steady tach signal after this - and then we can address the solution (you will not have to run the uS on a 9-volt battery...).

- Bruce

The crank wheel is a 30-2 wheel

I'll give these suggestions a try first thing tomorrow morning.

simplified wrote:Bruce,

The problem I'm currently having is the RPM dropping to zero during cranking. I have the VR sensor with the positive lead wired to the coax center and the negative lead wired to the shield, and the shield wire grounded to the same ground as the microsquirt.

My ignition input capture is on rising edge, and the cranking trigger is on calculated. I have played with the wiring and polarity, and the way it is currently set up is the only way I can get any sort of tach signal.

I think you made the same mistake that I did. The shield is the + input and the center connductor is -. Most electrical stuff that I have worked with has the shield as -.
The way you have it now the + input is shorted to ground.
Also a quote from the instructions,
VR return ground (Ampseal pin 33) - there is a separate VR(-) input on the AMPSEAL, this needs to be connected to the VR sensor(s). If you are using two VR sensors, return both back to this wire (these are low current and can be shared on the one wire return path) Do not ground the VR sensor anywhere else, return the ground back to the VR(-) terminal. On the MicroSquirt, this return goes directly back to the VR input circuit's transistor/op amp and not to the ground plane, this keeps the high amplitude VR voltages (and resulting currents) isolated to the VR circuit.

Just to add more data, I tried Simplified's msq last night on the bench. I used a 36-1 wheel with 18 skip teeth, so it's exactly equivlent to the 30-2 with 15 skip teeth. Everything worked properly and for info chan 1 spark occurred 17 deg before the first TDC which wason the rising edge of the 5th tooth after the missing one (because of the DElay teeth of 4). If there were no chan 2 offset the second TDC would be 18 teeth past the 1st TDC (180 deg) anhd since there was a chan2 angle offset of 103 deg, the chan 2 spark actually occurred 12 teeth (120 deg = 103 deg + 17deg table adv) before the second TDC. This was 6 teeth (60 deg) past the first TDC. It's not complicated if you draw out the teeth and use the 1st tooth after the missing one as the reference. With a 30 tooth wheel the same thing applies, except each tooth is 12 deg instead of 10.

grippo,

I believe my ignition settings are setup properly. I think the problem lies with the VR sensor. When the RPM signal is there, the engine starts to kick up briefly until the RPM signal goes out again.

I didn't get a chance to try Bruce's suggestions today, big exam tomorrow

I'll give them a shot tomorrow and post the results.

Sean

Last week I ran the microsquirt on a completely different battery and unhooked the ignition and injector connections. I tied the coolant, iat, and tps to 0 Volts. However, I still had the same problem of dropping the rpm signal during cranking.

Maybe the VR sensor and the microsquirt just don't agree with each other