Dropping RPM signal while cranking

simplified · Post by **simplified** » Sat Feb 02, 2008 10:11 pm

Having trouble getting my aprilia v-twin engine started. During cranking the rpm signal climbs, and then momentarily drops to zero, and climbs again. I have checked spark and fuel, both are sparking and squirting.

The ignition input capture is on falling edge, and the cranking trigger is on calculated. Coil charging scheme is on standard coil charge. I have removed the VB921's and placed jumpers to run LS1 coils, so my spark output is on going low.

The engine only has a crank sensor on a 30-2 teeth wheel. I am running dual spark, wasted spark. The engine is wired so that cylinder 1 fires 3 after the missing two teeth, and 77 degrees later cylinder 2 fires. My advanced ignition options setup looks like this:

Trigger wheel teeth : 30
Missing teeth : 2
Skip teeth : 15
Delay teeth : 3

Offset for Output #2 (degrees) : 103

I attached a couple datalogs of a cranking attempt, maybe you guys can see something I can't. Your input is greatly appreciated.

Thanks in advance.

simplified · Post by **simplified** » Sun Feb 03, 2008 2:19 pm

Any ideas?

Today I wired up just the VR sensor and ran the engine with another engine controller. The rpm signal is just not holding. The rpm's are correct when they're being read, but the signal comes and goes.

Attached is a datalog of the engine idling.

Post by **grippo** » Mon Feb 04, 2008 10:06 am

The rpms go from 1250 to about 2100 and the delta_ts (times between tach pulses = every 15 teeth) run from 10000 to 16000 microseconds. The latter is a +/-30% fluctuation. That's quite a bit for idling at 1000+ rpm, if those are the real rpms. You can try upping all three Pulse tolerances to be >40%. (If any are already over this, leave them as is, but set any that are under to 40%.) This is not a solution, but if it helps, it tells us that noise is likely the problem. If it doesn't, post your msq.

simplified · Post by **simplified** » Wed Feb 06, 2008 5:04 pm

The pulse tolerance didn't seem to help much.

Here is my msq.

Post by **grippo** » Thu Feb 07, 2008 5:05 pm

I don't see anything wrong with your msq. If you have a scope I would scope the inputs both coming out of the sensor and going into the processor. The fact that your rpm is erratic indicates the the sensor input input is either noisy, weak or the VR input circuit needs to be tuned.

simplified · Post by **simplified** » Sat Feb 09, 2008 9:55 am

How do i go about tuning my VR input circuit?

simplified · Post by **simplified** » Sat Feb 09, 2008 3:00 pm

We currently have a motec hooked up the same motor, and it runs the engine with no problems. I'm guessing it's the VR circuit, how do I go about tuning it?

Post by **grippo** » Sun Feb 10, 2008 7:37 am

I forgot that on microsquirt the circuit can't be tuned easily as it can on the regular MS2 boards. Since it is easy, try changing the tach input lead polarity in the inputs (rising edge to falling edge or vice versa). If this doesn't work I will set up and test your msq on the bench.

simplified · Post by **simplified** » Sun Feb 10, 2008 10:56 am

Yeah, I have done that several times. The way I have it setup is the only way I can get some sort of a tach signal.