I finally discovered the cause of my intermittent surge/hesitation. It turns out that my battery voltage reading is either dropping very low or spiking extremely high (20v at times). It only happens for maybe about 0.1 seconds at a time. This causes the ECU to compensate and it either pulls fuel or adds more in for a split second. I can't seem to find a cause for this. I have been testing various powers and grounds to the ECU with an oscilloscope, but none of them seem to show any erratic voltage readings when the issue happens. I even put an amp clamp on my alternator cable to look for a noisy alternator... Nothing. I think I'm going to go right onto the pins at the bootloader and measure there, because that seems to be a direct voltage feed. Anyone have any ideas why my battery voltage is jumping around?
(It's a V3 PCB with an MS2 card.)
Battery voltage spikes and drops
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Re: Battery voltage spikes and drops
Ok... So, just made a big problem out of a little one. I was probing onto the bootloader jumper pin (not the ground one, the other one) measuring the voltage on it, and it must have hit something, because all of a sudden the voltage on it dropped to 0, and I lost communication with the ECU. All of my megatune gauges dropped out. Oddly enough, the vehicle did not stall out. It stayed running, but has not started since. I tried re-flashing it, but it will not do this. Correct me if I'm wrong, but pin 27 on the daughter card should have direct continuity to the boatloader pin, shouldn't it? Mine does not.
Re: Battery voltage spikes and drops
Yeah, I was a bit misled into thinking one of the pins on the bootloader was a direct feed of voltage. I think I fried my daughterboard. Oh well...
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Matt Cramer
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- Joined: Sat Jul 03, 2004 11:35 am
Re: Battery voltage spikes and drops
It may not be that bad - try reloading firmware; this can sometimes revive a "dead" MegaSquirt.
Once that's fixed, you can go after the electrical noise.
Once that's fixed, you can go after the electrical noise.
Re: Battery voltage spikes and drops
Nope, didn't work. I think the fact that the car didn't stall but it lost communication with my laptop when I was fiddling with it is pretty telling. It didn't blank the chip out totally, but it is now in some kind of perpetual bootloader mode. 
Also, even though now I know better than to test voltage at it, the pin on the bootloader that is opposite ground only has 0.01V on it with the ECU powered up. Correct me if I'm wrong, but you need some amount of voltage on that pin, because how else would the module tell when it is jumped to ground and it has to go into bootloader mode?
I might even get lucky and fix my noise issue with a new daughterboard. I doubt it, but I don't see what else could be causing this. The powers and grounds did not seem to have any noise on them when watching them on a scope. There were a few blips of voltage here and there, but none that corresponded with when the car missed.
Also, even though now I know better than to test voltage at it, the pin on the bootloader that is opposite ground only has 0.01V on it with the ECU powered up. Correct me if I'm wrong, but you need some amount of voltage on that pin, because how else would the module tell when it is jumped to ground and it has to go into bootloader mode?I might even get lucky and fix my noise issue with a new daughterboard. I doubt it, but I don't see what else could be causing this. The powers and grounds did not seem to have any noise on them when watching them on a scope. There were a few blips of voltage here and there, but none that corresponded with when the car missed.
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Matt Cramer
- Super Squirter
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- Joined: Sat Jul 03, 2004 11:35 am
Re: Battery voltage spikes and drops
Try removing the daughterboard and see if the voltage on the bootloader opposite the ground rises. It should be 1/6 of battery voltage. If it isn't, check R3 and R6, as well as the trace along the top of the board that supplies 12 volts to the bootloader circuit, Q12, and Q9.
Re: Battery voltage spikes and drops
Yeah, I've got around 2V on the bootloader terminal on the PCB itself, but when the daughterboard is plugged in, I have basically 0V on both bootloader pins on the daughterboard. Oh well, now I know better then to start probing around on the daughterboard. I'm guessing I shorted it to some higher voltage, because obviously shorting it to ground doesn't hurt it. I think I saw my scope jump up for a second as well before the laptop lost comm.
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Matt Cramer
- Super Squirter
- Posts: 2951
- Joined: Sat Jul 03, 2004 11:35 am
Re: Battery voltage spikes and drops
Yeah, sounds like it. You might want to contact Peter Florance at pftuning.com - he can repair damaged daughter cards.
Re: Battery voltage spikes and drops
Just to update everyone, I put in a new daughter card, and got the car back to life. I didn't want to bother repairing something that is only $100, especially because I have relied on that car to get me over 400mi from home and back again. And you can't really have a megasquirted car towed to a shop if it breaks down. 
I'd just be more comfortable knowing something as delicate as the daughter card was professionally made.
Anyway, it almost seems like my battery voltage spikes were resolved with the replacement of the card, oddly enough. At the same time I put in the new card I upgraded to the latest MS2 extra release, so it could have had something to do with it. I'll have to drive the car more once the weather gets better, but for now it is looking pretty good.
I'd just be more comfortable knowing something as delicate as the daughter card was professionally made.Anyway, it almost seems like my battery voltage spikes were resolved with the replacement of the card, oddly enough. At the same time I put in the new card I upgraded to the latest MS2 extra release, so it could have had something to do with it. I'll have to drive the car more once the weather gets better, but for now it is looking pretty good.