Resolved 1G No Injector Pulse

[korbynclarke12]

First time poster long time reader.

So over this winter I've been building my 1991 Eclipse GSX. I've been having a weird issue where my injectors aren't getting a pulse, mind you I had the car running a couple months ago. So, I know I'm getting fuel to the rail and have good fuel pressure, compression is fine.

I sent the ECU out to ECMTuning and they said it was fine. I tried a different CAS and it didn't change anything. It has good spark but I put a new coil and transistor on it anyway. I can put power and ground to the injectors and they open just fine. I tried a different resistor box, the car will also run if starting fluid is sprayed into the intake, so that left me with checking the wiring. I tested the continuity between the four wires that go from the ECU to the injector plugs which are the ones that get grounded, and they all had continuity. I tested the power wires to the ECU, and it gets power where it needs, it also gets ground where it's needed (the ECU that is).

With the key on for some reason the four wires that go from the ECU to the injector plugs (yellow/blue, yellow/black, light green, and light green/white) all have voltage but the wires that go to the resistor box have none, why would it be switched like that?

I'm completely lost. And no the resistor box isn't plugged into the wrong plug. Any advice would be much appreciated.

 

[steve]

With everything hooked up, the ECU on but not cranking you should see battery voltage on both pins at the injectors.

If you not seeing voltage at the injector resistor it gets power from the MPI circuit and sends it to the injectors, it would seem that's the problem area.

When the ECU is trying to fire an injector if completes the ground side and pulls it's pin low causing current to flow from the MPI circuit to the injector resistor to the ECU. (Ignoring the real direction of current flow)

You have to have battery voltage at the injector resistor to power the injectors.

 

[korbynclarke12]

yes with everything hooked up and key on, theres voltage on both sides of the injector plugs, but with the injector plugs unplugged the wires that go to the ecu to be grounded have around 6-7 volts and the resistor box side has none, the resistor box is getting power too

With everything hooked up, the ECU on but not cranking you should see battery voltage on both pins at the injectors.

If you not seeing voltage at the injector resistor it gets power from the MPI circuit and sends it to the injectors, it would seem that's the problem area.

When the ECU is trying to fire an injector if completes the ground side and pulls it's pin low causing current to flow from the MPI circuit to the injector resistor to the ECU. (Ignoring the real direction of current flow)

You have to have battery voltage at the injector resistor to power the injectors.

it seems like circuit is backwards yk, voltage on ecu circuit but no voltage on resistor box side even though the resistor box plug has 12v on the red wire

 

[steve]

Easy to feel that way. What you don't see in the diagrams are all the internal circuits in the ECU and in this case there is more connected to the driver transistor collectors than just the wires to the injectors. Those (snubber) circuits cause the ECU pin to float at battery voltage when the ECU isn't trying to fire the injector.

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If you're not seeing battery voltage on the other 4 pins when you have battery voltage on p the red wire to pin 3 then the resistor seem broken. It's just four power resistors tied in common with the power and you should be able to measure about 6 ohms resistance between pin 3 and each of the other pins with it disconnected.

 

[korbynclarke12]

Easy to feel that way. What you don't see in the diagrams are all the internal circuits in the ECU and in this case there is more connected to the driver transistor collectors than just the wires to the injectors. Those (snubber) circuits cause the ECU pin to float at battery voltage when the ECU isn't trying to fire the injector.

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If you're not seeing battery voltage on the other 4 pins when you have battery voltage on p the red wire to pin 3 then the resistor seem broken. It's just four power resistors tied in common with the power and you should be able to measure about 6 ohms resistance between pin 3 and each of the other pins with it disconnected.

so there should be some voltage on the wires that get grounded by the ecu with the key on? tomorrow i’ll have to check the resistor box to make sure its alright and getting 12v

 

[korbynclarke12]

Easy to feel that way. What you don't see in the diagrams are all the internal circuits in the ECU and in this case there is more connected to the driver transistor collectors than just the wires to the injectors. Those (snubber) circuits cause the ECU pin to float at battery voltage when the ECU isn't trying to fire the injector.

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If you're not seeing battery voltage on the other 4 pins when you have battery voltage on p the red wire to pin 3 then the resistor seem broken. It's just four power resistors tied in common with the power and you should be able to measure about 6 ohms resistance between pin 3 and each of the other pins with it disconnected.

the resistance on the pins were about 6 ohms while disconnected, and theres power getting to the resistor, i also got this email from one of the people at ecm tuning after sending them a log and explaining my issue

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[jed344]

Have you tried a NOID light? This confirms injector's plug is pulsing when cranking the car. The 12v on both pins on each plug is correct. The ecu then grounds to fire that injector circuit. This generally happens to fast for a multi meter to pick up but a noid light will flash. When this flashes you know 100% the circuit is acting as expected. When this does not flash then it will indicate a issue.

When the ecu side wires test good for continuity between injector plug's and ecu i have yet too see it being the ecu failing to ground the circuit personally. Would expect many other things would be acting up in that case.

Normally it is MPI side as that supplies the power as stated, are you seeing 12v on the other 4 pins on the 4 injector plugs? The side the mpi feeds, if you are not then there is the issue.

 

[Brembo]

Just a shot in the dark, this past summer I worked on relocating fuse box along with battery. Once semi completed, I decided to run the car to make sure it is still operational. Long story short I mixed up the connector on resistors box with a connector by the throttle body. The give awey was resister box was getting really hot while the car was not staring. Just a small check, other wise pull injector diagram and start chasing.

 

[steve]

What did this turn out to be caused by?

 

[korbynclarke12]

What did this turn out to be caused by?

for some reason i didnt have a good connection between the resistor box plug and harness plug, i pulled out the insulator and what not and she fired right up