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Megasquirt cuts in and out during cranking

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On my last 15 minute drive, the car began to run poorly, setting in slowly at first, but getting worse and worse. 10 minutes in it would barely idle, and by the time I got onto my block, it stalled completely. I was able to restart it once and pull into my driveway, but that was it, the engine would not restart again.

 

First thing I checked for was spark. It'll spark, but only intermittently. One or two random sparks every second or so. Hooked up the laptop, and it turns out Megasquirt is shutting off when I crank the car. All the gauges in megatune will go red, and then they'll pop up for a split second, showing the correct rpm, and then go right back out again. It's not resetting, as the counter in the bottom right never says so, and the computer doesn't beep. It just shuts off during cranking (and I would assume during running as well, with the problems I had, but I can't start it to see).

 

With the key in the on position, but the engine not running, megasquirt is on fine, the fuel pump cycles on and off, and I can see my air and coolant temps, map pressure, etc.

 

I made no physical or software changes to the car to bring this on. It's been running flawlessly for almost a year, and I didn't touch anything or change any wiring to bring this on. I cleaned the grounds, to no avail.

 

I'm stumped as to why it would start doing this. Any ideas at all?

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Thats really weird. It doesn't seem to be loosing power if it's not counting resets. What it could be doing is losing the RPM signal. Are you using the ZXT distributor? You might want to check your wiring to that.

 

Also, on my dad's install, we managed to pinch one of the wires inside the DB37 connector and it was shorting out with the case, causing a similar problem. Check the innards of that too.

 

If you can't get it to work this afternoon, give me a call, I'll swing by with my box and we can try swapping it out.

Mario

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No, no pull up. It's not needed (or possible, if I'm not mistaken) because I'm running the vr signal directly into megasquirt, not through an hei module. I'm wondering if the coil thing in the vr dizzy has gone bad, but I'm not sure how to test it. I remember reading in a service manual that it was supposed to have a certain resistance (around 400ohms if I remember correctly), but I never got that reading in the first place, even though it worked. I don't have an o-scope or access to one, so I can't scope it.

 

I pulled the megasquirt board and visually inspected it, but could not find any burnt wires or bum solder joints or so forth. All the joints that looked remotely like they could be bad passed a resistance test fine.

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Have you checked your battery? If your battery is weak then when you crank it the volts drop low enough that megasquirt turns off. Could also be your relay going bad and losing volts at that. Put the voltage display on your labtop and see if they drop below 10v? while cranking.

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The voltage display through megatune won't work because megasquirt stops responding to the laptop, nothing shows up at all. There are dips below 10v on the portions of the log that do show up, but that's because the battery is almost dead from cranking after every change to test it.

 

Also, keep in mind that this started happening while the engine was running, and got so bad the engine quit.

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Sorry if I missed it...are you running a relay board? If so I would start by swapping the main relay just to try something diff. Maybe swap with the FIDLE relay. I suppose you could isolate some wiring by powering MS directly from the battery. It should still be fused so no danger there.

 

I understand that the battery was normal when this all started but what does it read now when using a voltmeter?

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The voltage display through megatune won't work because megasquirt stops responding to the laptop, nothing shows up at all. There are dips below 10v on the portions of the log that do show up, but that's because the battery is almost dead from cranking after every change to test it.

 

Also, keep in mind that this started happening while the engine was running, and got so bad the engine quit.

 

Could be a bad alternator. Charge up the battery fully or try a known good battery. This happened to me once.

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Thumper's first post got me thinking, so right after I answered him, I went outside to have a look at the relay that powers megasquirt. Took it out, tested it (worked fine) and put it back in...Viola, car started right up. All of the connections were clean, so I don't know what was going on, but it's working now. I'm going to grab a back up and throw it in the glove box in case this one is on it's way out or something.

 

Thanks to all for your help.

 

And on a side note, thanks Thumper for the recommendation on the bullet mufflers, the exhaust I built with one is the best sounding system I've had yet.

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Nice that you got it running.

I swapped out the headgasket in a backyard the day you called, so mine's running also.

 

About the relay, my fan one did the same thing. I thought it was bad because my connections were good so I unplugged it and plugged it back in with no issues at all...

 

Stupid electronics...

Mario

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Yeah, almost makes me wish I had a carb'd v8. Almost. Playing with megasquirt is just too much fun though.

 

Awesome that yours is running too...again. How many headgaskets is that now? Time for an intercooler perhaps?

 

We need to meet up so you can hear my new exhaust, and so we can figure out who's is faster. (You've got the displacement, but I have the compression).

 

And where was your sig pic taken? Somewhere on the north side, I would guess?

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This Friday SIR will be having a test and tune. $20 to run all night.

I need to Seafoam my car and install a new HEI module. It seems my module is getting heat soaked because if I run my car hard over and over again my tach goes crazy over 5k rpms and I start to ping on the top of 3rd and 4th.

 

I have new fuel in there and my a/f is almost rock steady at 12:1 and I've retarded my timing and it still does it, but only when it's heat soaked.

I ran it just warmed up last night and it pulls like a mofo when it works right :)

Mario

 

EDIT: Pic was taken up at the end of Grant, turn left, then a right at the police academy and it starts to go uphill. There was a little turn off there so I stopped and took the picture.

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Damn, I'd love to head down there, but I'm heading up to Sedona friday afternoon. SIR's website says they do test and tune almost every friday night, but their schedule only shows it once a month or so?

 

And I saw your car last night in the ece parking lot just after 7

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