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

I have a MSII V3 running the 2.89 code. I have had some problems with tuning the unit as I have been doing it in an on again,off again fashion. I had driven the car on weekends with some tuning when possible. Today I wanted to retime my engine. After powering down the engine I removed the tan jumper that feeds my 7 pin HEI. When I went to restart the car the MSII had no power. There is 12V going into the relay board. But the LEDs do not illuminate and there is no communication.

When I first built the unit I had a "no power condition". Lance helped me isolate the issue down by having me remove varios diodes. I did the same today with no luck. each time I removed the diode the unit still did not power up. For the test I removed D8,D10,D11,D12 and D4. There are no signs of any obvious burns. Could MOV1 be the issue ?

My MSII has been very reliable. I really want to start dedicating some serious time to tweak my set up. Any help would be appreciated.

Thank you.

Dan

To check for a short in the Megasquirt PCB, power up the Megasquirt on a Stimulator or on the car and check the following points for voltage with a multimeter.

You should find the same voltage as the battery voltage on the following points: S12, S12C, the center legs of Q9 and Q12, the left (non-banded) end of D3, the left leg of U5, and the left (banded) end of D9.

You should have 5 volts at the following points: S5, the two +5V holes in the proto area, the right (non-banded) end of D9, the right leg of U5, the left (banded) end of D19, and pins 1, 20, and 31 of the CPU.

Let me know where you find the correct voltages, and where you find the wrong ones.

Hi Matt,

Thank you for the quick reply. The voltages are as follows:

s12 - 12v
s12c - 11v
q12 - 12v
q9 - 12v
d3 non banded - 12v
u5 - left leg near db9 - 12v
d9 - left banded end - 12v


s5 - .4v
proto holes- ~.5v
d9 - non banded - 5v
u5 - right leg towards db37 - 5v
d19 - banded end - barely 1v
pin1 - 0v
pin 20 - 0 - .2v
pin 31 - 0v

Thanks.

Dan

Ok, something's shorted on the 5 volt plane. First try removing D19; it's the most likely component to blow. Does that change the readings?

Hi Matt,

After pulling a leg on d19 I was able to restore the 5V outputs at all points except on the db37.



s5 - 5v
proto holes- 5v
d9 - non banded - 5v
u5 - right leg towards db37 - 5v
d19 - 5v
pin 1 - 0v
pin 20 - 3.45v
pin 31 - 0v

Can I assume that this voltage (on pins 1 and 31) was not present due to the disconnected d19 diode ? I did have 3.45V (digital 5V) on pin 20.

Thank you.

Dan

daniel wrote:Hi Matt,

Can I assume that this voltage (on pins 1 and 31) was not present due to the disconnected d19 diode ? I did have 3.45V (digital 5V) on pin 20.

Thank you.

Dan

No, you cannot; D19 is for overvoltage protection on the 5 volt plane. Something else is broken. Does the voltage change if you unplug the daughter card?

Matt,

After uplugging the daughter card there was no change in voltage for the db37.

pin 1 - 0v
pin 20 - 3.45v
pin 31 - 0v


Thanks.

Dan

Check if L1 is broken or C19 is shorted to ground.

Also, what exactly do you mean by calling 3.45 volts "digital 5V?" It's not enough voltage for the ECU to work with.

Matt,

I removed L1 from the circuit and had continuity when checking between the 2 legs (not burned open).

I removed C19 and could not make continuity between the 2 legs after holding the ohm meter to the legs for several seconds.I put C19 back in the circuit and checked for a ground reference. It did have a ground on the side closest to the db9. The side closest to the db37 did not have a ground reference.

And for my statement earlier calling 3.45 volts "digital 5V , I was under the impression that the 5V level on MS was being used for an IC circuit where 0 - 2.3V = digital 0, 2.7V - 5V = digital 1. Bottom line: Please excuse my ignorance here. Also, so there is no misunderstanding, all other 5 V references that I wrote earlier were in fact between 4.9V and 5V.

s5 - 5v
proto holes- 5v
d9 - non banded - 5v
u5 - right leg towards db37 - 5v
d19 - 5v

Thanks.

Dan

3.45 volts is acceptable for a sensor input, unacceptable for a power connection. First, I'd check the resistance from L1 to pins 1 and 19.

Matt,

I got the car running again. For starters, I never built the jumper for th IAC motor as I am using a fast idle valve. So that explains no +5V at pin 31. As for pin 1 and pin 20 I did not reference the ground off pin 19 as suggested in the assembly manual for MS V3. Once I did that I was able to get the 5V. I am not sure why my other ground was able to provide the other voltages but not on pins 1 and 20.

So, I replaced D19. Then, I was able to start the car with full communication. I appreciate all of the help that you gave. I am sure you saved me a ton of time !

BTW, my car is a 1954 Cadillac Series 62 - 2 door with a 1970 Cadillac 472 with 1975 Cadillac fuel injection with a 1981 V8-6-4 HEI 7 pin distributor.


Thank you.

Dan