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Trained (ex)Professional, , 1953-2018 RIP
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16,232 Posts
I think one must consider that the injector pulse dropping out may not be the cause of the engine stall but the symptom. I'd try the following;

Hook up a voltmeter to coil positive
Install a spark tester on one sparkplug wire
Install noid light

Start the engine and observe the above.
If the voltmeter drops before the engine stalls, suspect power feed to the coil (ignition switch for example).
If voltage remains good but spark drops out, suspect ignition system (to include a shorted tach).
If both voltage and spark remain good, suspect fuel management.

It's difficult to diagnose a problem without knowing where to look.
 

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Trained (ex)Professional, , 1953-2018 RIP
Joined
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16,232 Posts
It would appear then that the coil power source and the ignition system are in good order. That leaves fuel management. The fuel ECU though, having been replaced with a known good unit, can apparently be ruled out as well.

The fuel ECU pulses the injectors by providing a ground. This means that one of the two injector wires must be hot with key on. Is it? Injector power is supplied from main relay terminal #87.
Also check for ignition system pulse at fuel ECU pin #1. This signal comes from ignition coil terminal #1 (negative side).
 

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Trained (ex)Professional, , 1953-2018 RIP
Joined
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16,232 Posts
...indicating the ground is not being provided by the ECU, no?
Correct. The ECU is not providing a ground to pulse the injectors.

...and pin 1 has full battery power with key on.
Pin 1 is the pulsing signal from the ignition system (coil negative). Without it, the fuel ECU thinks that the engine isn't cranking or running and will not pulse the injectors. Please check the voltage at pin 1 with the engine cranking (a dwell meter can be used here as well). You should get a pulsing voltage reading.

The grounds to which Elio refers are attached to the cam cover just to the rear of the auxillary air valve.
 
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