I may have have the low ecm voltage problems solved :smile: Its NOT the alternator. My ecm volts on datamaster were like 12-13v so today I spent most of the day checking for voltage drops, multimeter and wiring diagrams in hand. After tracing wiring diagrams and checking voltages, here is what I found. Our ECM has Two batt power wires that stay energized all the time. On theECM connections, B1 and C16, both are orange. There is also one power wire that is energized with the ignition, A6, pink/blk.
To make a very long story a little shorter. I was only getting arround 12.5-13 volts at B1 and C16 and arround 13.2 at A6 with all the lights on. Judging by the guage of the wires and the setup, I believe the ECM pulls most of its current from the B1 and C16 that have power all the time and the A6 is mainly just to power on the ECM. As it turns out, both the B1 and C16 wires are fed from the ECM B fuse in the fusebox. Checked voltage there...13.2v. Random voltages in the fuse box ranged widely from about 12.5 to 14.0v.
So here's what I did.
1) Get a 14guage fusible link from NAPA with a round metal connector on the end, about 4 ft of 14-12 guage wire, some female spade connectors, and this metal connector that is made to slide in with a GM plastic fuse to tap in a wire to that fuse. Get the larger size.
2) Solder the open end of the fusable link to one end of the wire and insulate with heat shrink.
3) Disconnect the batt cable and hook up the fusible link to the alternator power connection.
4) Run the wire through a grommet in the firewall and over to the ECM B fuse. Cut off the excess, but leave some slack.
5) Strip wire and put on the spade connector. The Female spade connector will then connect to the fuse tap connector thing.
6) Pull the ECM B fuse and hook on the tap connector. ON THE RIGHT SIDE FACING. I considered it very important to put it on the right side of the fuse, because this is the source voltage side of the fuse and the circuit still needs to be fused for saftey.
After I did all this, My voltages at B1 and C16 with all the lights on and idling were at 14.05v. This is over 1 volt greater than it was before! The voltage gains on A6 were not as high, since it works through the ignition switch, but it was still good at 13.6v with all the lights on. Voltage on the ALDL connector was at 13.5-13.6volts. Datamster confirmed this with 13.5-13.6v with all the lights on, idling.
I feel like the voltage at B1 and C16 are the most important and are not shown on datamaster, though I could be wrong. Anyway I hope this may help some of you with low ecm voltage problems. Before you blame the alternator, take some voltage readings.
To make a very long story a little shorter. I was only getting arround 12.5-13 volts at B1 and C16 and arround 13.2 at A6 with all the lights on. Judging by the guage of the wires and the setup, I believe the ECM pulls most of its current from the B1 and C16 that have power all the time and the A6 is mainly just to power on the ECM. As it turns out, both the B1 and C16 wires are fed from the ECM B fuse in the fusebox. Checked voltage there...13.2v. Random voltages in the fuse box ranged widely from about 12.5 to 14.0v.
So here's what I did.
1) Get a 14guage fusible link from NAPA with a round metal connector on the end, about 4 ft of 14-12 guage wire, some female spade connectors, and this metal connector that is made to slide in with a GM plastic fuse to tap in a wire to that fuse. Get the larger size.
2) Solder the open end of the fusable link to one end of the wire and insulate with heat shrink.
3) Disconnect the batt cable and hook up the fusible link to the alternator power connection.
4) Run the wire through a grommet in the firewall and over to the ECM B fuse. Cut off the excess, but leave some slack.
5) Strip wire and put on the spade connector. The Female spade connector will then connect to the fuse tap connector thing.
6) Pull the ECM B fuse and hook on the tap connector. ON THE RIGHT SIDE FACING. I considered it very important to put it on the right side of the fuse, because this is the source voltage side of the fuse and the circuit still needs to be fused for saftey.
After I did all this, My voltages at B1 and C16 with all the lights on and idling were at 14.05v. This is over 1 volt greater than it was before! The voltage gains on A6 were not as high, since it works through the ignition switch, but it was still good at 13.6v with all the lights on. Voltage on the ALDL connector was at 13.5-13.6volts. Datamster confirmed this with 13.5-13.6v with all the lights on, idling.
I feel like the voltage at B1 and C16 are the most important and are not shown on datamaster, though I could be wrong. Anyway I hope this may help some of you with low ecm voltage problems. Before you blame the alternator, take some voltage readings.
