ECU's being fried

[steve]

I dont understand what the ignition switch has to do with it and why it does it with the ignition off.

The IC110 circuit board controls the activation of the MPI relay. When the ECU is off it needs a way to turn the MPI power on so it can turn on. The ignition switch run position send battery voltage to ECU pin 110 and that goes to pin 1 of IC110 the circuits on that board then pull pin 4 low which is connected to pin 63 on the ECU and that turns the MPI relay on. When you turn the car off you'll notice that the MPI relay stays on for 5-10 seconds after turning the ignition off.
As to why your is chattering after turning off I haven't a clue. Clearly pin 63 is connecting to ground somehow intermittantly. On the one board you showed you have burning going on in the general area of the backup power circuit. It's bad enough that I wouldn't trust anything that's going on with it in the car.

At this point you have no choice but to sit down with the multimeter and start making sure you don't have anymore shorts in the sensors, solenoids or wiring. You need to get at lease one of the two bad ECUs fixed to the point where your sure they aren't causing the problem.

With the ignition off you should see battery voltage at pin 63 and 64. They shouldn't go low until you turn the ignition on.

Steve

 

[Dweet]

How much voltage is "low"? Like 5v or 0v? Ill probe those pins and see whats going on before and after turning the ignition on. As for pin 63... where does that wire trace to?

 

[steve]

How much voltage is "low"? Like 5v or 0v?

As for pin 63... where does that wire trace to?

Low is 0v or within a few tenths of 0.

Wiring diagram

Steve

 

[Dweet]

I mean where does the wire coming from Pin 63 run in the car? I was curious if you knew its route and its ending point. If it goes from pin 63 to pin X on the MPI relay why not just cut the wire and then run it directly from the ECU to the MPI relay eliminating where its shorting out at?

 

[steve]

One, you don't know that it is shorting out.
Two, you already know where it goes down to the pin on the relay. I can't tell you how it gets routed, you'll have to look for yourself if it turns out to be a problem.

Between the VFAQ, the wiring diagrams linked, and what's available in the archives here you should be able to track down what your problems are and fix them.

Steve

 

[Dweet]

I guess I'll try pulling pin 63 and see if I get the same result. But if its not pin 63 im going to be stuck