Looks like I Miss-wired the after market COR relay and blew out the FC pin driver on the ECU. I had accidentially wired in +12v switched to the relay lead which was also connected to this this pin and was causing the after market COR relay to "buzz". I corrected the problem but it looks like the FC pin is no longer grounding as it should. I have manually wired the relay into the ignition switch +12v and directly grounded it out to the body as a temporary work around to get the engine running but don't want to keep it wired this way because of a potential fire hazzard.

Is there some other way I can wire the COR relay to engage the fuel pump so it only runs when the engine is running/cranking and turns off when the engine dies (but key is on)?

It's running now but if I don't fix it properly I can see this happening down the road...

 

You're probably not going to like my answer (which is how I'd do it, btw).

Looking at the EWD for my 97 4Runner (I'm sure they're all mostly the same in this regard) at the FC terminal there is a resistor between between the pin and the BJT (a transistor) that the ECU uses to connect the ground (think of it as an on/off switch; the resistor and wire coming off the middle of the BJT is the "on/off" signal that's wired into other logic in the ECU). Chances are you overloaded and "popped" the resistor in series with the BJT and/or the BJT itself.

You're going to need to open the case of the ECU, locate the FC pin, then locate the trace (copper "wire" embedded in the PCB), follow that (visually or using a volt meter) until you find the resistor (or look at the board and if there's a black spot, that looks burnt, you've found the problem area). If the resistor looks ok, use your volt meter to measure the resistance across the resistor if it says anything like 0 or 1M that resistor is shot and it'll need replacing. You'll need to replace it with a resistor of the same resistance and power rating; this will be a bit of a challenge to find, it should have a resistor code on it (either colored lines for a "through-hole" part or a decimal number printed on it for a "surface-mount" part).

Follow the trace from the other side of the resistor until you find the next component, that should be the transistor, and it should have a part number printed on it.

I would replace both parts, if it were mine, and to do so, you'll need to de-solder the old compoents from the board and I recommend using some solder wick (braided copper wire; google it there's lots of demos on youtube), then solder the new parts down.

I know you'll have lots of questions feel free to ask any question you have, and definitely post pictures of the opened ECU and the parts in question and I'll do everything I can to help you from here.

Or you could take the easy route and just buy another ECU.

 

Hey Sac I like your signature layout, look similar to mine! But yeah, OP, I'd just get another ECU and call it good. Unless you have more time than money, then crack it open! If you crack it open, let us know and take pictures along the way.

 

what is the cor relay?

 

COR = Circuit Opening Relay

 

It's just a standard relay used to send voltage to the fuel pump at the appropriate time.

 

Hmmm... Not sure I want to open up the ECU. Might consider it if it was through hole but not surface mount. My soldering skills aren't that great and some surface mount parts are really small... Also thinking these are potted units (board covered/sealed in Epoxy)

Anyone know if the ECU is through hole or surface mount? It's a 1999 Tacoma 4x4 MT ECU

PS: Thanks for the reply. That really is good info
Thanks again

 

Not likely.
Could be both.

The way to find out is to open it up.

 

You may try a stereo/tv repair shop.

If not, I'd replace it. No telling if that drives another circuit or something. Too much to chance for me.