Troubleshooting TBI

Working on a 90 K2500 with the 5.7 TBI, manual trans.

Story goes that the truck quit on the road, after a short time it started for a little bit, quit again, and has not started since. It has spark and power to the injectors but the ECM will not ground them.

Here is what I've tried.

1. ICM replaced.
2. Plugged in a presumed good distributor and spun it by hand (to eliminate a bad pickup coil). Can hear it firing the coil, but no ground to the injectors.
3. Manually grounded injectors at ECM plug with a power probe, injectors will spray and the truck will start for a second from the gas in the intake. (means wiring from ECM to injectors and fuel pressure are good)
4. Tried applying +12v to the Purple/White wire on the 4 pin distributor connector (was told this would create a test signal that fires the injectors), nothing happened.
5. Checked for power on the fuel pump signal wire, it's working.
6. Checked sensor and chassis ground wires at the ECM, they show ground.

Here is the strange part. I'm not getting a 5v reference signal to the MAP or TPS. Nothing on the sensor plugs or on the gray wire at the ECM plug.

I unplugged the ECM and tried checking for power from the ignition switch, could only find one that had switched power (I believe it was black/purple). I don't remember seeing any constant power. If anyone could tell me the location and color of the wires that are supposed to provide switched and constant, it would be appreciated. My diagram seems to have omitted them.

According to the diagrams B1 and C16 should be battery power (constant/unswitched) on the ecm. Check the ECM B fuse. The diagrams are here: http://www.gearhead-efi.com/Fuel-Inj...Information-42
All of the C3 ECM's for TBI use pretty much the same pinout. I recently replaced a 1227747 with a 1228746 and disabled the IAT in the bin. Plug and play. 16146299 will do the same.

Hope this helps
Brian

Quote:

---

Originally Posted by MrGiggles

Working on a 90 K2500 with the 5.7 TBI, manual trans.

Story goes that the truck quit on the road, after a short time it started for a little bit, quit again, and has not started since. It has spark and power to the injectors but the ECM will not ground them.

Here is what I've tried.

1. ICM replaced.
2. Plugged in a presumed good distributor and spun it by hand (to eliminate a bad pickup coil). Can hear it firing the coil, but no ground to the injectors.
3. Manually grounded injectors at ECM plug with a power probe, injectors will spray and the truck will start for a second from the gas in the intake. (means wiring from ECM to injectors and fuel pressure are good)
4. Tried applying +12v to the Purple/White wire on the 4 pin distributor connector (was told this would create a test signal that fires the injectors), nothing happened.
5. Checked for power on the fuel pump signal wire, it's working.
6. Checked sensor and chassis ground wires at the ECM, they show ground.

Here is the strange part. I'm not getting a 5v reference signal to the MAP or TPS. Nothing on the sensor plugs or on the gray wire at the ECM plug.

I unplugged the ECM and tried checking for power from the ignition switch, could only find one that had switched power (I believe it was black/purple). I don't remember seeing any constant power. If anyone could tell me the location and color of the wires that are supposed to provide switched and constant, it would be appreciated. My diagram seems to have omitted them.

---

disconnect the tps and try to start it.

Quote:

---

Originally Posted by sturgillbd

According to the diagrams B1 and C16 should be battery power (constant/unswitched) on the ecm. Check the ECM B fuse. The diagrams are here: http://www.gearhead-efi.com/Fuel-Inj...Information-42
All of the C3 ECM's for TBI use pretty much the same pinout. I recently replaced a 1227747 with a 1228746 and disabled the IAT in the bin. Plug and play. 16146299 will do the same.

Hope this helps
Brian

---

Sorry for the OT...thanx for that bit of information. I sorta asked this very question...ironically if I did a search I would have found my answer as there's an old thread about swapping the two ecms. I supposed I asked the wrong question...so no one replied to my query as I was asking about relocating the EGR delete wires into the IAT positions to run an IAT when I could've simply deleted it's function in the bin. Well, i figured ANLU was closest thing to a 5.7L TBI w a L98 cam that is. Maybe one day I will try it for fun!!!