I think that engine may have an oil pressure switch in the path for ECM control of the injectors. Check that oil pressure switch to make sure it is working. Should have 3 wires on it. Orange, gray and tan possibly. Orange wire should have 12 volts on it going into the oil pressure switch. 12 volts is then sent to the PCM, (when the switch operates) on the gray wire to indicate good oil pressure.

 

The fuel pup

 

To help you along with Silver's recommendations here are some schematics.

Here is my diagnostic procedure:

Check both sides of the fuses designated for the TBI power.
No blown fuses, next will be the oil sender portion of the diagnosis. Crank the motor until the oil pressure light goes out or you see the oil pressure gauge rise. If neither of them don't do anything, replace the oil sender unit with the right type (gauge or idiot light).

Once you get the appropriate fuel gauge in place, not leaking. Make sure the gauge is sitting at zero P.S.I., turn the key on and crank the motor for 5 to 10 seconds. Did the fuel pressure get to 9-13 psi within 2 seconds of cranking? If you had fuel pressure, did the fuel pressure "hold" above the 9 psi level for at least 1 minute?? If not, the fuel pressure regulator need to be changed

If the fuel pressure slowly rose, it's a weak fuel pump / restricted fuel filter. Change both.

No fuel pressure, check for 12 volts at the fuel pump relay on the tan/white tracer wire or some systems red /white tracer wire. Voltage will be present when the oil pressure is above 4 psi only. Look for a random single female pig-tale with those listed wire color colors in the cowl area or the area of the fuel pump relay. Apply 12 volts to that female pig-tale. Crank the motor. If the motor starts it's the relay, If not, either an open back to the fuel pump, or the fuel pump has failed.

Part of the cranking diagnosis, it has to be determine whether the fuel injector solenoid is getting a voltage signal to fire the injector.
Since I know you don't have a node light, find a digital volt ohm meter (DVOM), set it to register to read above 12 volts. One side of the injector connection will have 12 volts. I think it's the red and white wires which will be 12 volts to ground. If not, check both sides of the Inj A 10 amp fuse for being (open) blown. Once you know you have 12 volts at the injector, install voltage probes into the female side of the injector harness and crank the motor. Did you see an unsteady voltage increase???

If yes, injector is getting a signal.
If no, with the battery disconnected, remove and reinstall a few times the ECM connector.
If above action doesn’t correct the problem, either open in fuel injector circuit or defective ECM.

Now to the schematics.

 

New
Many thanks Motor City and Silverado, I was aware the oil pressure sender could shut off the fuel pump, but didn't know until now it sent signal to the ecm concerning the injectors. I have run the fuel test, and the fuel pressure is good. if I ground each injector at the ecm connector I get a good cone of fuel spray with the pump running. Will check for signal from the oil pressure sender. And the schematic of the fuel system is one I don't have, thanks again!

 

Actually the oil filter sending unit does not shut it off. It is an auxiliary fuel pump enable in the event that the deal pump relay has failed.

Sidenote: something that can happen related to the oil pressure sending unit is that if the sending unit feels internally, as in it shorts out, it will take out the fuel pump circuit fuse. Mine did that once, it would fire and start and as soon as the pressure built to activate the switch, it would blow the fuse and kill the truck.

 

FIXED! Oil pressure swith was it. Many thanks!

 

Nice!!!

 

Ok. Im running(or not) a '93 C1500 5.7. same issue. I am getting power to my injectors, but not ground. New ecm, new oil pressure switch. I can ground straight to the frame and the injectors stay on. Thoughts?
Good fuel and oil pressure, i do know my timing is off (my toddler "helped" with the timing, but I have spark. The engine is very picky with timing. I could knock the distributor slightly out of line and not run.)
I just want to get my injectors to fire, the rest I can do. Someone commented somewhere that they tied the ground to the transmission wiring, but i couldn't find any more information on it.

 

I am getting power to my injectors, but not ground. New ecm, new oil pressure switch. I can ground straight to the frame and the injectors stay on. Thoughts?

The ECM grounds the injectors (in pulses) when it's told your engine is turning over or running. The ICM sends a Reference Signal to the ECM (in this case pin B5) which, then grounds the injectors as needed. Maybe you don't have a good connection or bad ICM? Check your grounds at the T-Stat too. If you have spark I wouldn't think the pickup coil in the dizzy is bad. Here's a wiring diagram of the ICM and where the wires go. YMMV

It’s not a good idea to leave your injectors on continuously. They actually do cycle on and off and do not continuously spray.

^^^X2 - it probably wouldn't run for long until it got totally flooded.

 

It’s not a good idea to leave your injectors on continuously. They actually do cycle on and off and do not continuously spray.

 

Yea, replaced the icm about a month ago. Didn't change anything. If i could find the pin for the wires, I'd check continuity, but as it stands, when i turn the engine over, I'm reading a constant 3 k ohms from the ground wire at the injectors to the ground.
Any ideas on what I should be ready across the connector at the icm?

 

I'm reading a constant 3 k ohms from the ground wire at the injectors to the ground.

When you test injectors you use a noid light. You can also take a 9v battery and wire it to each injector to see if it clicks.

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Edit: I just remembered you grounded them and they spray - forget the battery thing.

 

What Peter is telling you, is that the problem is probably not in the ECM (and you've proved that by a swap), the problem is external to the computer.
The computer provides a ground (switched ground) for each injector, when told to do so.
So, 2 places to look.

• the ground for the ECM, ensure it is there.
• the signal to turn on the ground for each injector as, and when, required. These signals come from the distributor, see Peters drawing.

 

Ok. So i replaced the ecm, and still had no pulse. That is the reason I replaced the icm. Im confident that something somewhere is open. This is because I have a power getting to the injectors, but no ground. If the icm isn't sending the right signals, or if the ground wires are bad going to the ecm, or if the ecm it's self has a bad ground ( though I would think I'd have bigger problems first), these would make sense.
I realized I forgot to post this initially, but new ICM, ECM, Oil pressure switch, injectors, and air filter.
Peter mentioned checking ground on the T-stat. Thermostat?
And sorry if I sound up-ity. My truck has been sitting for almost 2 years, and I wasn't allowed to work on it for $$$ reasons, and my wife finally said to fix it and wont get off my butt about it.

 

Hmmmmm, truck or wife............hmmmm.

 

Yea... And the truck is a month younger than me, and i plan on keeping it until my oldest, 7, can drive it. Just gotta keep it going till then. (Each kid gets a vehicle. My middle child gets the motorcycle, 93 Suzuki intruder)

 

Sounds like you are missing the ground from the battery to the body and or the body to the engine. Check the continuity of the ground cables at the battery to the body, since the ECM is grounded to the body, and the ground from the engine to the body. That should fix you up.

 

Ok, so the grounds are good. I triple checked them, from random points all the way to the pin on the ecm. Im going to have my wife help me to check the signal wire points. Maybe one of them has grounded out or broke.

 

So, you checked the grounds and they are all good. Next, I would be using a noid light to check the ground pulse coming out of the ECM to the injectors, will need to consult the shop manual for the specific wires. I use a wire piercing probe and then just dab some silicone on the tiny hole afterwards. If it flashes then, the ECM is sending the signal, if not, then the wiring from the ECM to the injectors is bad. If the truck has been sitting for a while, then perhaps you have rodents who have chewed through some wires.

 

Duh, if the noid light does NOT flash, then the ECM is not sending the signal to trigger/ground the injectors, suggesting you may still have a bad ECM or bad ground. My mistake.

 

Or........the ECM is not being triggered to send the ground pulse.

 

Thats what I was thinking. The ecm has the potential to give ground, and the injectors are getting power, so something isn't giving the ecm the go-ahead. What kind of power should I see coming out the signal pin on the icm? (How much and when)
Im currently flooded so I need to pull my plugs to verify spark and try to reset timing on the distributor, but I think I will just leave the plugs out until I get the injectors working to avoid any excess strain on my battery and starter. Don't want to lock it up with gas.