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

currently trying to tune the microsquirt ecu for my formula sae team. we leave for competition in about a week and currently dont have a running engine. heres whats happening...

rpm signal is showing upwards of 20k rpms when cranking
tps signal is fine
map sensor reads fine

heres what we have, 18-1 flywheel with a vr sensor for rpm signal.
whenever we set the skip teeth to anything but 0 we have no rpms when cranking, when at 0, we see 20k again.
not completely sure how to configure the teeth settings in megatune think its
trigger teeth-18
missing teeth-1
skip teeth-1 ??
delay teeth-????

we mounted a 12-1 wheel and sensor on a bench just as a test subject and spun the wheel by hand, still getting about 8k rpms

can someone please point me in the right direction, im in desperate need of help here. once i get the rpm signal wokring properly we can start setting up ignition timing and actually tuning the engine.

here is a scaled drawing. there is a total of 18 teeth including the one larger tooth then all the others

If you would post your msq. and which firmware you are using it would be a lot easier for someone to help you.

What version of the code are ou running? Early versions ( before October 2007 ) just used the vr in as tach out. My 36-1 wheel pegged my tach at idle. New versions provide a correct tach out.

firmwear - 2.881

The engine is a Suzuki LTR 450 (2006) for our Formula SAE project. It is an 18-1 flywheel, variable inductance crank position sensor. It used to have a taller tooth flywheel that we cut the tall tooth off tonight. We no longer get cranking rpm to be in the range of 40k, but now more like 1200 rpm. It got better, but still not correct. Engine still wont crank over either.


Thank you for all your help guys





FYI - dimensions of the teeth are .2" space between teeth is .6", and the gap where the missing tooth is is 1.4"

Here is the msq

I don't think version 2.881 had the tach signal fix. I think it was added in one of the 2.883 versions. I would try downloading the 2.883j version.

Just to clarify a couple things so the problem is clear, the problem we have is getting the correct signal into the microsquirt and/or getting microsquirt to process the signal correctly. The tac provided in megatune is reading in the 1000-2000 rpm range in cranking when it should be reading around 100-500 rpm. We don’t have a external tac setup yet... originally we had a 18-0 tooth pattern with one unusually large tooth. The pic above doesn’t show the whole picture (have to download to see it). We took the large tooth of and now we have a true 18-1 tooth trigger wheel. I had a test fixture setup in a lathe with a 12-1 tooth wheel and VR sensor and the tac in megatune consistently read 3 times the actual rpm the wheel was spinning on the lathe. It seems as though the rpm is, again, being multiplied by some variable but I don’t know how to change it. It appears to be seeing the rpm change correctly but the number is just larger. I'll try updating the firmware on the ecu and then testing the sensor again.

I put 2.883j in the controller and still have the same problem. do i need to update megatune as well? when I boot up megatune it asks for which project, the most current option available is "MS2-MicroSquirt BG 2.881" is this correct or is there a later version that i should have and be selecting?

I looked at your msq. and found a couple of problems.
Yor tach signal masking is wrong for a decoder wheel. Read this part of the manual.

In the code are two input variables to control the interrupt masking to prevent false triggers. These are changed in the 'Ignition Set-Up/Base Ignition Settings' dialog of MegaTune:
Time Mask time (milliseconds) after tach input capture during which further interrupts are inhibited to mask coil ring or VR noise, and
Percentage Mask is the percentage of the predicted interval before the next tooth (dtpred) after the last tach input capture during which further interrupts are inhibited to mask coil ring or VR sensor noise.
For wheel decoding you must use values close to 0.2 ms and 10%. However, to not break any existing setups, the default values are 0 and 50%, the same values that are 'hardwired' into pre-v2.5 code. Be sure to adjust these values when you set up for a trigger wheel (note that they are in a separate dialog from the trigger wheel settings).

You need to set your skip teeth to 18.
Tou might try setting your cranking trigger to calculated instead of trigger rise.
Are you sur your VR wires are connected properly. There were a few harnesses that had the shield and center connector reversed.
Just as a side note, your req fuel setting looks really high for a single cylinder 28 ci motor.
Did you use the trigger wizard and a timing light to set your trigger offset?