no power to injectors after swap (5.7 vortec)

[Turbokat]

I have been swapping my 99 2dr tahoe (originally a 6.5) over to a more typical 5.7 but i can't get my rebuilt engine to fire from its own fuel.
I had a security issue in the beginning but after re-learning it lights up under bulb check as normal.
the engine ran fine out of the donor suburban.
It does run with starting fluid until its all burned up.
fuel pressure is above 50 psi.
Tested with 2 different PCMs with the same result.

I had my friend using a multimeter and check if the injectors got any power but absolutely nothing came up.
it really feels like the PCM doesn't want the injectors to spray at all
i have been searching on the web this entire evening with no luck

any ideas?

 

[L31MaxExpress]

I have been swapping my 99 2dr tahoe (originally a 6.5) over to a more typical 5.7 but i can't get my rebuilt engine to fire from its own fuel.
I had a security issue in the beginning but after re-learning it lights up under bulb check as normal.
the engine ran fine out of the donor suburban.
It does run with starting fluid until its all burned up.
fuel pressure is above 50 psi.
Tested with 2 different PCMs with the same result.

I had my friend using a multimeter and check if the injectors got any power but absolutely nothing came up.
it really feels like the PCM doesn't want the injectors to spray at all
i have been searching on the web this entire evening with no luck

any ideas?

12VDC is provided to the injectors through a keyed power supply in the fuse block that is hot in both Start and Run positions. The PCM grounds each injector. If you have a power supply issue to the injectors it is not PCM related.

 

[east302]

Do you have good spark at all eight cylinders (using a tester)?

Is the “service engine soon” light coming on when the ignition is first turned to run?

I wonder if there is a way to rig a noid light up to see if the injectors are being grounded by the VCM during cranking. When you tested for voltage, were you grounding through the injector ground (which wouldn’t always be active) or to somewhere else?

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It looks like the VCM grounds at pins 17 and 18 in connector C3 (think it’s labeled white on the box). See how those look on the harness side. G103 is the one by the thermostat, but I’m not sure where ground 104 is; it may apply only to the 454.

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[Turbokat]

the SES light is on while cranking but no codes appear
i have about 1.9 ohms when testing the ground on top of the thermostat housing to pin 17 and 18
when testing inside the injector plug i get about 5.3 to 5.4, is there something I'm missing?

 

[east302]

the SES light is on while cranking but no codes appear
i have about 1.9 ohms when testing the ground on top of the thermostat housing to pin 17 and 18
when testing inside the injector plug i get about 5.3 to 5.4, is there something I'm missing?

With ignition on, were you getting battery voltage when testing from each of the eight feed cavities on the injector harness to battery negative or an engine ground? I wouldn’t test using the harness ground that goes to the VCM...I’ve read that exposing it to battery voltage isn’t a good thing for the electronics.

The resistance looks low enough from the VCM to ground. I suppose if the pins were damaged then you’d have a whole lot of other issues.

Next step would probably be to confirm that the VCM is grounding each injector. I’ve seen a noid light used on those with individual injector plugs, but am not sure how you’d do it here. Maybe have small leads from the light that will allow you to probe the injector harness cavities and then see if it flickers when cranking.

Maybe someone has done that and can chime in.

And you have good spark on all eight, correct?

Fuel pressure spec is technically 60-66 psi with ignition on. Were the diesel tank, lines and pump swapped out or are they the same for gas?


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[Turbokat]

All fuel lines and pumps were replaced and I am getting battery voltage at the injector plug. My fuel pressure gauge may be failing me but they don't sell them at the store where I live. The fuel lines are brand new and the pump is reused from the donor truck. Im pretty sure i have good spark but I haven't checked it because there is no fuel smell at all inside the throttle body. I'm going to test with my noid light now

 

[Turbokat]

Well I tested with a light (not really a noid light) with injector 5 and 7 and it didn't light up at all

 

[east302]

If those two do light up when using an engine ground but not when probing the respective ground terminals and cranking, then the VCM isn’t grounding them for some reason.

I guess check for continuity from the injector harness to the VCM connector C2. It looks like it comes in at #12 and 15.

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[Turbokat]

Okay I'm into something now. Thank you for giving me the idea to check the wire from the injector plugs to the PCM. Seriously this has to be the problem lmao. So just for those wondering. There was an aftermarket LPG system on the donor truck I removed. I thought the wires were Y splitted in a way. Well no. The wires goes from the PCM to LPG ECU and back to the main harness. And I just clipped through the wires before I started on this project (like I didnt think it would bite me in the a** later.) I just re-opened the wireloom and found this

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[Turbokat]

Do you know what this wire is? It is also chopped for some reason. It's coming from the black connector

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