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nickbenjones

ecu will not fire injectors

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Stock EFI system on an L28. I have swapped to a gm style HEI module. New Harness.

The injectors will not fire, pin 10 on ecu is seeing 12v, all injectors have 12v on both pins reference to ground, and the car runs fine with starter fluid. I know i have spark, the tach wire is wired from ECU pin 1 to the negative terminal on the coil. Do i need to wire in a dropping resistor for the ecu to see the pulse? Does the car need to see a start signal to begin firing the injectors? Does the ecu need to see 12v through the air valve from the fuel pump? any help would be greatly appreciated.

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Have you verified the ground circuit to the ECU connector for each injector?  The 12 volts on each side is from the parallel power supply (someone on classciczcar explained that to me, Captain Obvious), but doesn't tell you that the ECU is controlling ground.  Have you checked fuel pressure?

 

Good that you've verified spark with starting fluid.  Why did you change the harness?  If the ECU is good, and it controls ground, and gets the Pin 1 signal, with fuel pressure the engine should run.  Pin 1 is branched with the tach also.  Does the tachometer work when it's on starting fluid?  If it doesn't, you might not have a good Pin 1 signal.  The ECU is sensitive to the signal quality.

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yes the ground circuit to the ecu connector is good. fuel pressure is good. there is no tach in the car currently so its hard to tell if the signal is good or not. sucks to hear it come to life with starter fluid then watch it die. I replaced the old harness because the oem one was hacked by the previous owner.

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The coil negative circuit is an odd one.  It connects the tach, the ECU, and the old ignition module.  One wire, branched.  I've had two cars, a 76 and a 78 that would not run without the tach installed, using the stock ignition modules.  But, since I've installed a GM HEI module, the 76 will start and run without the circuit to the tach complete (removed the resistor and it started).  But, the tachometer doesn't work right with the HEI module unless I have a capacitor on the coil negative terminal.  Lots of cross-talk possibilities there.

 

Did you disconnect the old ignition module under the dash?  Maybe you didn't and you're getting enough anyway to break the coil circuit but not enough to trigger the ECU.

 

You didn't say why you swapped harnesses.  Year of car would be good too.  Good luck.

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Put the tach back in.  Take the condenser off of the coil.  See what happens.

 

A simple way to test the system at super-slow speed is to connect a wire to the coil negative, turn the key on, and tap the wire to ground.  Every three taps should cause the injectors to click.  Three sparks is one engine revolution.  Might be a simple way to test variations.  If you get injector clicks,maybe you're just firing bad gas.

 

Too bad you're on a phone.

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