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2G Injectors not firing

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oldmanfrost

15+ Year Contributor
111
17
Mar 22, 2009
Tampa, Florida
Hey guys, having an issue where my injectors aren't firing via the harness, but the car runs fine on starter fluid. I pulled, cleaned, and tested the injectors directly they spray fine when powered manually.

I confirmed voltage at all four harness plugs with a test light, but the injectors won't pulse while cranking. Since positive power is present, it seems like the ECU isn't pulsing the ground.

Could a bad CAS (cam/crank sensor), bad ground, or blown ECU driver cause the loss of the ground signal? Any ideas on what to test next?
 
Yes the ECU relies on CAS and Crank signal to fire the injectors. Sometimes you'll get spark if one goes out, sometimes not but most of the time it won't have fuel if either signal is lost.
 
Checked for fuel pressure? Any diagnostic codes?
Yes checked pressure.. that was the first thing that was handled. Given power from outside source. To jump an injector with the plugs out , while cranking and fuel sprayed out the cylinder.

Yes the ECU relies on CAS and Crank signal to fire the injectors. Sometimes you'll get spark if one goes out, sometimes not but most of the time it won't have fuel if either signal is lost.
Okay, I will test those two sensors.
 
CAS sends signal to ECU to tell it to fire the injectors so you may have blown the ECU drivers, or bad CAS, or bad wiring. But first test the 4 injector current limiting resistors (box on firewall) for proper 5.5-6.5 ohm resistance each to rule that out (note that even if the resistors are way too high resistance preventing the injectors from firing, you will still see +12v on the injector harness).
 
It's harder on a 2G to test the cam and crank sensors than on a 1G where you can turn the CAS by hand and watch the signals switch voltage. You need a good multimeter or an oscilloscope to see them on a 2G.

Noid lights don't always work on our cars and because of the short pulses used for the injectors you again need something like an oscilloscope to see them.
 
But… The issue is all connectors produce a signal ( captured by led light 💡) when cracking.

All injector fire when powered by an independent power source ( injector tester ).

However when the connectors are connected to the injectors, they don’t seem to have the current to activate the injectors.

It’s as if the harness produces a signal but not a power source, think voltage divider how it’s useful (Vout) to create a signal to measure - usually by (GPIO) pins.

but it would not be capable of powering a actuator.

This makes me suspect some kind of ground latching interruption, having no knowledge of the circuitry I don’t know if the CAS / Crank sensor are the interruption or if it’s a device in the ECU

Lastly - a spare resistor box was used during testing and the results were the same.
 
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