Could you clarify which ecu you are using?
You've posted the diagram for a 90 model year ecu, and it's a bit of an orphan here in the states.
There are several fundemental configurational differences between it and the 91 up units used here in the states.
... one of those differences is how the ecu picks up the tach pulse.
miss Jeff O. and Steve P. at times like this!
The kiddies on the intawebz will jump all over the 6 and 14 thing, but they miss the way the tach is "read" at the ecu.
I don't pretend to understand them, I just know they exist, as I had to run additional wires on a swap that involved a 90 4g63 into a pickup to get the tach and fuelpump to work correctly. (sadly, that was over ten years and many
beers ago, and the details have slipped from my memory)
In addition to the 90 and 91 up yearly change, I *believe* the jdm/other market ecu's *may* have some other configurational differences.
... I'd say pm Baz, as he seems to really know his stuff on the jdm cars, but, well, that may not work so well in this case.
You *might* be able to find/verify the trigger wire on the back of the mpi relay and trace it back to the ecu by color (and verify with an ohmeter) to determine which terminal the mpi relay "expects" to be grounded/controlled by the ecu.
I don;t knwo if this will help, but a few years back, I waded thru this with Amar on an evoIII ecu. (thread found here
In that case, the fuel pump driver is on pin #8, (and as an aside, it has the same color as the usdm units white with a red tracer
That said, the stratedgy for controlling the fuel pump worked in the same way as all the other mitsu ecu's I've worked with.
There are two
coils in the mpi relay for the fuel pump circuit.
One is hardwired to the key and
ground for use while the engine is cranking. (power is fed from the key thru the relay coil, and then thru a dedicated ground)any time the key is in the crank position, the fuel pump is "on"
The other coil is the run coil.
Power is fed to the inny of the second coil with the key in the run position, and the ecu will control the ground leg of that relay coil
... allowing ground to the relay coil only when it "sees" a frquecny signal from the cas
no cas signal = no ground = no fuel pump
This meant as a safety feature to turn off the pump to prevent the pump from continuing to feed a post shunt fire.
At any rate, a clarification on which ecu you are using will go a long way towards helping us figure things out.