Programmable output question

[E4ODnut]

The 2001 Dodge Ram that I am working on has what Chrysler calls an Automatic Shut Down relay. The ASD relay supplies power to the injectors and ignition coils, as well as a few other things. It essentially operates under the same conditions as the fuel pump relay. I would like to enable another output to do this and think I have it figured out, but I would appreciate an opinion.

I'm not using the output port PP6 - VVT so I can select this as the output port. Power on value should be off, as MS will enable it when it is ready to. Active value should be on. The output channel porteh status can be used with PortE4 (bit 4) that controls the fuel pump relay. Because I want the ASD relay to operate with the fuel pump relay I should be able to use the = operator, set the threshold (bitmask) to 16 (bit 4) and leave the hysteresis (match) at 0.

Anything wrong with my reasoning?

[jsmcortina]

As it is another low side relay, just connect it to the fuel pump ECU output. The two will then switch on together.

James

[E4ODnut]

The stock wiring has the power supply for the relays coming from separate fused sources, so I would prefer to have them controlled by their own output.

[jsmcortina]

Beware of backfeeding with a different power source.

James

[E4ODnut]

Ah yes. Now I recall reading something about that in the hardware manual. The ASD relay coil gets it power source from a fused connection that is hot at all times.The fuel pump relay coil gets it power from a fused connection to key power that is hot in start/run. MS is supplied from this source as well, so it looks like I have to get around the ASD connection somehow. I prefer not to change the stock wiring so I think the easiest solution would be to just install a pilot relay with the coil supplied from the same source as MS and the fuel pump relay that would be wired in parallel with the fuel pump relay. This pilot relay would then control the ASD relay.

But now I am curious as to why the mid current outputs have this restriction. I had a look at the schematic but I didn't see anything obvious. Perhaps it has something to do with the IPS0226 low power Mosfet, but I don't know enough about them to say.