Hi, I had some issue with my swap last summer and ended up realizing that my problem was probably coming from my megasquirt.
I have a MS1 PCB V3.
My problem :
-I have no RPM in the megatune, but all other sensors are working
-> No RPM = no tach signal.
I finally took the time to test the megasquirt with stim on an oscilloscope at school today.
I probed the tach signal at 3 different area on this simplified tach signal circuit :
This is what I got from pin 24 on the DB37 connector :
*That signal look clean to me.
The second signal I took was the one after R12:
** This is where it gets tricky, I don't know if it's fine, the signal seem to be damped alot....
*** And, I have no way of comparing with another megasquirt to see if it's fine,
The third signal I took, the one between the opto-isolator and directly at the input pin of the MS1 CPU pin 14 :
**** That signal look like crap, it looks like it is full of noise
***** Once again, I have no clue if this is right or not.
So, I would like to know if someone out there can tell me if my second and third signal should be looking like this or not.
I'm thinking maybe :
A) R12 is failing
B) The opto-isolator is failing (probably the case, looking at the noise)
C) The CPU input is dead...
I'm looking forward at any suggestion. thank you!