Was on the dyno today trying to fine tune things before the trip to FL for the GRM$2013 Challenge. Was working up in the 8500 rpm range when the thing shut off. I read in megamanual do not burn while running. A very experienced Megasquirt tuner told me just do it at idle. I was, but it still hurt it.
Fuel pump sounded different so I thought I was out of gas. Filled up and attempted again. Noticed that I had no tach reading when trying to start. Diagnosed and determined it was ECU.
Brought it home and opened it up. R12 is burnt. You could smell it before opening the case.
Hoping this is all that I need to replace.

 

Megamanual suggests increasing the r12 value to anywhere between 470 ohms and 1K. Any thoughts out there

 

Hopefully R12 is the extent of the damage. I've burned many, many times when the engine was running, but either at idle or a steady, low MAP cruise/overrun condition. I was under the impression that the risk was more to either the coils (possibly a much longer dwell, burning them out) or to the engine itself b/c of wildly inaccurate timing.

The schematic for the V3 board is on bowling & grippo's site: http://www.bgsoflex.com/megasquirt.html This could help you to trace down any other potential faults too.

8500 range? Is this on an S5 N/A or RX-8 (i dunno, maybe rolled a few times or something)? S4 and S5 stationary gears tend to break around 8500, so for the sake of reliability I'd keep the redline at 8000 or 7500, considering you'll be spending a lot of time there.

Edit: after looking on the B&G site for what R12 does, it looks like its only used by the hall-effect or optical input for the tach signal. If you're using the stock S5 crank angle sensor (variable reluctance), this resistor isn't doing anything, and thus really can't be the cause of your problems. I don't know about the RX-8.

 

I've never heard if an issue with burning while driving. I usually try to do it on devel just to avoid the slight hiccup, but still have had probably over a thousand burns and no issue.

 

It is an S3 12a turbo. We used to rev ours S1 and S2 12a to 10 on the autocross courses. 8500 was where I had planned to stop my tables. I was unable to make my final pulls to get a final plot. Hopefully I can get the thing fixed today as I still have some cosmetic stuff to finish.

 

R12 replaced still have issues. Zener diode was bad too. Replaced it and still have issues.
I was testing with multimeter and have voltage everywhere in the circuit. I bumped two terminals on U3 and the tach went crazy on the laptop. Any ideas???

 

Are you using a CAS or a coil negative fed through the Hall Effect circuit in fuel only mode?

Which Zener was burnt? Are you talking about D12? Possibly

It is possible the 4N25 is blown, that is what it is there for, protection. There could also be tracks inside the PCB that are burnt. I would start by removing all those parts cleaning the board and using the continuity function to check that points on the board that should be connected are still connected. I would also test U3 out of circuit.

Other parts other than U3 are worth a mere few cents, might be worth just replacing them all as well.

 

fuel only and negative coil trigger. Not gonna make the challenge this year.

 

d2 was burnt. Per megamanual section ms2.v3.51b install 22v or 24v zener diode in reverse orientation for negative coil triggering, not quoted, but that is what is said

 

checked U3 as if it was a diode at terminals 1 and 2. Test showed open in both directions. Tested 4, 5, and 6 as a transistor and it tested good. This is the hall/coil - sensor. Is this the correct testing method?

 

Call ben at DIY autotune ((678) 261-8789)

 

Picked of anther 4n25 optoisolator then went to Radio Shack. They did not have any desoldering wicks, so I bought the $18 pump. That was yesterday.
Today, I installed the new U3. We are back in business. Car cranks and runs now. Hopefully it is back on the dyno Sunday.