Injectors not firing anymore.

[simsumdum]

Hi,

I am working on a friends Megasquirt, it has been working for a few months, then after him moving some stuff/wiring around in his truck the injectors will no longer fire.

After testing it here's what I found:

-the injector outputs are fine using the stim board, both lights blink as they should.

-when I attach the injectors on a jig on my bench, the injectors do not fire and the lights on the stim board are very dim.

-i have replaced most of the injector driver circuitry, but this does not fix the problem.

-removing Q14 and Q15 allows the injectors to fire, this appears to be part of the current limiting circuit that protects the mosfets (apperantly calibrated to ~15 A as per the schematic), my injectors are fused at 3A.

-Shorting resistors R37 and 38 does not disable the current limit circuit as it should.

PCB V3 and MS1 for reference.

Any ideas??

Thanks!

[Matt Cramer]

Sounds like Q14 and Q15 may have been burned. What is the resistance on these injectors?

[simsumdum]

I believe they are about 15 ohms or so.

I have replaced Q14,15 twice now. Not too sure why they would be getting burned out especially while being tested on the bench..

This is deffinately a strange one.

[trakkies]

Hi,

I am working on a friends Megasquirt, it has been working for a few months, then after him moving some stuff/wiring around in his truck the injectors will no longer fire.

After testing it here's what I found:

-the injector outputs are fine using the stim board, both lights blink as they should.

-when I attach the injectors on a jig on my bench, the injectors do not fire and the lights on the stim board are very dim.

[snip]

How are you feeding both the injectors and the stim?

[simsumdum]

I am feeding both the MS Stim and the injectors off of a 11 volt lipo battery. The battery voltage is sufficient as the injectors fire with another MS and also with the current megasquirt minus Q14 and Q15.

[trakkies]

I am feeding both the MS Stim and the injectors off of a 11 volt lipo battery. The battery voltage is sufficient as the injectors fire with another MS and also with the current megasquirt minus Q14 and Q15.

I was really asking how you'd connected the injectors and stim to the MS at the same time.

But how are the injectors firing minus Q14 and Q15?

[Matt Cramer]

I am feeding both the MS Stim and the injectors off of a 11 volt lipo battery. The battery voltage is sufficient as the injectors fire with another MS and also with the current megasquirt minus Q14 and Q15.

I was really asking how you'd connected the injectors and stim to the MS at the same time.

But how are the injectors firing minus Q14 and Q15?

Removing Q14 and Q15 disables overcurrent protection, but the injectors will fire if they're out.

[simsumdum]

I am supplying the stim board with the lipo, one lead on all of the injectors are all tied to the positive of the same lipo, then the second lead of 4 injectors are tied to bank one output of the ms, and the second lead of the other 4 injectors are tied to bank 2.