blew C16 trying to get MS-II set up; help

[thr3shold]

Got a V3.0 MSII with 2.905, relay board, MSD6a, mopar. Hooked up the MS to get signal from distributor(VR triggering) and then send ignition signal to MSD unit. I'm suing a previous Holley pro-jection 2d install, so I'm re-using the wiring where possible (injectors, TPS, coolant sensor). I got everything hooked up and when cranking, no injectors fire and no spark. Double checked my connections and realized the 12v memory connection on the relay board was never hooked up, so I hook that up then crank it and I hear a frying sound and smoke coming out of the MS. C16 is black and puffy. I know I installed it with the correct polarity. I've looked around the forum for another cause, but couldn't find a solution, any ideas?
Thanks

[thr3shold]

btw I used the stim as I was building and passed all the checks and got tunerstudio to read data from the MS with the stim attached

[thr3shold]

OK, installed a new C16, all Fry's had was a 35V cap so I threw that in and it seems to work OK. I rechecked all of my connections again, did some tests, and tried starting it up again, the new 35V cap bubbled a little but hung on (voltage spikes I guess), but still no go. New symptom is that after cranking the engine for around 5 seconds or more the distributor starts buzzing like a capacitor! I unplugged the VR wires from the distributor and it stopped and it doesn't seem to do it if I crank the engine for short bursts. Now I'm more perplexed than when I started.

[Matt Cramer]

Sounds like you have a voltage spike issue. How exactly is the MS grounded?

[thr3shold]

The megasquirt is grounded to the chassis at the relay box chassis ground stud, the negative VR wire is sent through the unused MAT ret wire (no MAT hooked up yet) and the LC-1 controller is grounded through the clt ret (the coolant sensor is hooked up, but gets grounded through the threads)

[Matt Cramer]

The megasquirt is grounded to the chassis at the relay box chassis ground stud,

Chassis grounds often are rather noisy, and they can get worse if you are trying to run several things through one bolt. Try grounding the MS to the engine block instead.

the negative VR wire is sent through the unused MAT ret wire (no MAT hooked up yet) and the LC-1 controller is grounded through the clt ret (the coolant sensor is hooked up, but gets grounded through the threads)

Other than that you've left off the MAT, that would sound reasonable for the older 7-wire LC-1s that included an analog ground. If your LC-1 has six wires, ground it to the block; its ground wire sinks too much power to run it through the return terminals.

[thr3shold]

I have one of the newer LC-1s so I will make those changes when I get home from work, I was going to have to eventually since I plan on installing the MAT sensor in the near future.

[thr3shold]

I made the changes to the grounds, but it still won't fire the coil. I used a cheapo oscilloscope to make sure I was getting a good signal from the distributor and nothing out to the MSD. Also, I put the MS2 into injector test mode and verified that it will fire the injectors, so there's that.

[Matt Cramer]

Do you have a data log of the "distributor buzzing" behavior?

[thr3shold]

Unfortunately I do not, I'm not sure I even could get one since I can't connect to the MS2 without it running. I played with it some more last night and it did not do it again, though to be fair I didn't crank it over long enough to trigger it like I did previously.

[Matt Cramer]

Can you connect to the MS2 on a Stim?

[thr3shold]

Yes, I can connect fine with my stim, save new settings to the MS2, adjust all of the knobs on the stim and have them read fine in tunerstudio.

[Matt Cramer]

Ok. So at what point do you lose the connection?

[thr3shold]

If I unplug the stim, I lose connection or if I have the MS2 plugged into the relay board I can see the LEDs on the MS2 light up, but it either says can't connect or no data/input I can't remember which right now.

[Matt Cramer]

or if I have the MS2 plugged into the relay board I can see the LEDs on the MS2 light up, but it either says can't connect or no data/input I can't remember which right now.

Ok, let's focus on that point. LED lights up, but you're having trouble connecting. What exactly does the computer say?

[thr3shold]

I am not near my car right now, but I did hook up the stim just now to the MS2 and I could see large square waves on pin 24 and much smaller ones on pin 36

[thr3shold]

OK so I found a problem. I was extending the USB cable after the serial to usb adapter and it was preventing me from connecting to the MS2 unless it was connected to a stim. Also, I got it to fire a couple of times, not consistently, but some is infinitely more than none.

[trakkies]

OK so I found a problem. I was extending the USB cable after the serial to usb adapter and it was preventing me from connecting to the MS2 unless it was connected to a stim. Also, I got it to fire a couple of times, not consistently, but some is infinitely more than none.

If you need to extend your connection, use a serial extension cable. I've found the serial side is less fussy than the USB one. If you have difficulty finding the correct cable get an ordinary serial one and change one end to a male. A good idea anyway as it allows you to make one of the correct length for your needs. Or make one up from scratch using a decent quality balanced microphone cable - this will be more flexible than ordinary ready made cables.

[thr3shold]

Got it running finally. Two main problems that I discovered, one was the I disconnected the switched +12V wire to the MSD 6a accidentally and that I hooked up the fuel pump the way it was with the pro-jection and the MS2 runs it opposite to that. I've got the ignition the way it was originally, I'm going to get my fuel tuned in more before I try that again next weekend. Thanks for everyone's help.