ecu problem?
 

OK so I bought an 84 gslse and it doesn't run. I took off the upper intake manifold to test some things to find out the injectors aren't getting a negative signal while cranking the engine. The Haynes manual shows that those signal wires come straight from the ecu. I don't have another ecu or any electrical spare parts to test at the moment. Could it be something else or is my ecu bad?

keep looking! is the ecu getting power? is the ecu getting an RPM signal from the trailing ignitor like it should?

Haven't pulled the ecu out yet. The tachometer bounces when I turn it over, does that mean that it has rpm signal and power to the ecu?

if the tach is bouncing then the ignition should work, but it doesn't mean the ecu sees power.

its not a new car, the tach is run right from the ignition, and the ecu ONLY does fuel, and emissions controls.

Do the GSL-SE's have the separate ECU fuse holder right on the side of the ECU, like the older units do?

First thing I'd check, if yes. Nobody ever finds those damn things.

Well it gets spark to all four spark plugs and the there is plenty of fuel pressure. Should I just pull the ecu cover and test the ecu power wire?

i'd check the fuses first, but yeah. mazda ecu's very rarely fail, its probably not the problem

OK ecu has power. While I had the ecu cover off I checked the injector signal wires directly from the ecu and turned the car over and still no injector signal. Checked fuses and the fuses are good. Fusible links are also good. Car has fc fusible link block so its easy to tell if the fusible links are good or bad.

Check output from CAS next, I'd think...

84-85 13bs don't have a cas they still have distributors.

you need to check the TACH signal wire. it comes from the trailing ignitor, and one branch runs the actual tach, the other gives the ecu the RPM signal.

Tachometer works fine. I sprayed some starting fluid just to here it start while I'm trying to figure out what's wrong and she started right up idled really high at 4k for some reason then died. So basically the car would start fine if I could figure out why the injectors aren't getting any signal and get the injectors working.

Have you tried testing the wire that comes out of the ecu and goes to the injectors?

Wait, are you sayin that at the ECU pins for the injectors you have 12v constantly? The hot side of the injectors is ran rite off the relay so if its not getting a ground and pulsing the voltage then yes the ECU is gone. One way to check if you have it all apart is to unplug the injector and take a self powered test light and ground it to the chassis and check availabe voltage at the inj. connector. THen use the light like a jumperwire across the connector and crank. If it doesn't light up like it did when it was grounded to the chassis, then the ECU is toasted.

Yeah that almost exactly how it is and its be confusing the shit out of me. The black and yellow wire on both injectors has a constant positive 12v while the ignition is on and the second wire on both injectors is supposed to be a negative signal wire which when I start the car the wires get no signal at all but when I connect a ground wire to the the signal wire on either injector the injectors (with the fuel pump on) click on and spray fuel everywhere. Make sense?

Oh and yes I did also check all the wires with my volt/ohm meter and confirmed all this.

So I'm still not getting injector signal and I just replaced the ecu. Anybody have anymore ideas?

yeah, the main relay (err its called something else i think) supplies power to the injectors, and the ecu grounds the circuit to fire it.

the ecu will pretty much fire the injectors as long as it gets power and an RPM signal.

so the circuit looks like this:

battery->main fuse->relay->injector->ecu->GND.

the RPM comes from the trailing ignitor, and tees off, with one branch running the tach. the RPM signal i think should also turn on the fuel pump.

Well unfortunately for me the main relay is good and the ecu is getting an rpm signal. I even replaced the ecu and that didn't work. So basically I have power to the ecu, I have an rpm signal, I know my injectors are good but yet still no injector signal. Oh and the fuel pump is turned on by the afm. It only turns it on when the afm flapper door is open.

yes but its probably not the ECU, as you've replaced that. i want to say the junction for the tach wire is actually by the coil, so the ECU tach wire and the tachometer wire start at the same place but are actually separate.

I had the same problem i connected another ground wire from my negative battery terminal to a good body ground then deflooded it i know this sounds dumb as hell but i have an se with all original wiring and somehow it fixed it but it will be flooded afterwards so do the deflood procedure i have been driving mine like this 120 miles a day for 6 months now fires up even in the dead of winter no prob let me know if it helps