Help! Capacitor Broke on ECU!

Yep..... the typical electrolytic capacitor leakage failures. You need a 47 µ farads 16v.... and while you're at it, also replace the other capacitors.... another 47 µ farads 16v for the top center and a 10 µ farads 63v capacitor for the center-right small one. Also make sure the surrounding board lines aren't open due to damage from the electrolyte.

caps like that are used to store energy, set up timings and the like functions. It looks like there is either a timing IC (8 pin) near that cap so I am guessing its some kind of PLL or timing circuit.

It's a plain old boring polarized electrolytic bulk bypass cap.

If it's on the 5V, then get one rated for at least 15V. Get anything between 10µf -> 47 µfarads. Get one that has a voltage rating of at least the same as the old one.

Basically, that cap is used to help smooth out the power that goes to the chips. It'll smooth out power noise below ~10KHz->100KHz. For higher speed power noise, the smaller non-polarized caps are used.

You can get one/more at Radio Shack, or Ebay.
Get something cheap, like:
http://cgi.ebay.com/10UF-50VOLT-RADIAL-CAPACITOR-LOT-OF-25_W0QQitemZ250256508778QQcmdZViewItem?hash=item250256508778&_trkparms=39%3A1|65%3A1&_trksid=p3286.c0.m14
or
http://cgi.ebay.com/10uf-400V-Hi-Temp-Radial-Electrolytic-Caps-10pcs_W0QQitemZ300232062413QQcmdZViewItem?hash=item300232062413&_trkparms=39%3A1|65%3A1&_trksid=p3286.c0.m14

As long as it's between 10µf -> 47µf don't worry. The cap was chosen because that was a part they bought in bulk. There is not anything "magical" in the choice between 10µf -> 47µf for a bulk bypass cap for that type of circuit. 47 is nicer because it stores ~5x more energy. But, it's also much slower to respond and has a poorer response rate than the 10.

It's better to populate using more 10µf caps on many places on the board. But, that drives up cost. When you make a few million of these things a year, $1 extra per unit becomes a big deal.