Wire size: Powering the Fuel Pump -- Vaporworx, GM Engine Controller

[sjaroslo]

I am trying to get some of the new wiring installed in my 67 Camaro so that I can work towards engine fire-up. I have a GM Crate LSX454 and am using the GM Engine Controller; also, an AAW complete wiring harness.

Although there is a circuit set aside in the AAW harness to run an electric fuel pump, there are also provisions to do so from the computer, and I think that this is probably the better solution. The power will actually be flowing to a VaporWorx PWM DC controller driving a CTS-V pump.

Here is my question. There is 1 vacant cavity on the rear body harness and I was going to run my fuel pump power feed in that connector, and was planning on using 12 gauge wire. However, I just re-read the Engine controller documentation, and it says this:

"The fuel pump is controlled by the ECM. The control wire supplies 12 V and is fused/relayed and should connect to the 12 V side of the fuel pump using 10 gauge wire (minimum size)."

I can deal with that (although I just bought some 12 gauge wire thinking I was golden) but here's the wire that is coming from the Engine Control fuse panel; there's no way that this is 10 gauge wire--doesn't it become the weakest link, then?:
81200

Thanks for your input.

[sjaroslo]

OK, hang on.... The actual POWER to run the fuel pump is coming from the DC Controller, which is coming from the BATTERY directly; the line from the Engine Controller is only a TRIGGER wire, in this application (although the engine controller doesn't necessarily know that). So a 12 gauge wire from the engine controller to the input of the DC Controller/PWM should be just fine at 12 gauge, right? It isn't going to be provided the power for the load.... Yes? Please weigh in; I guess I need to start letting this stuff soak in to my head for a little while before running here and posting up a question!!

[CarlC]

Steve,

There are a couple of different scenarios that you may have going on here, so let's look at 'em.

First, you are correct that using the ECM to turn on/off the VaporWorx controller is the best method. This allows the safety features of the ECM to remain functional. Using just the IGN-ON fuel pump circuit in the AAW harness will not allow the use of this feature.

Next, it's a bit hard to tell, but that looks to be a 12ga wire that they want you to run to the "fuel pump." If so, this is likely connected to a relay since most ECM's don't have that power capability. Here's where two different things can be done.

The first is to route that 12ga wire to the blue wire on the VaporWorx controller. This will act as the on/off trigger. A 20ga wire is more than sufficient for what is needed here so don't be afraid to go down on wire size and make your routing easier. I do suggest trying to use a similar colored wire to make future diagnostics easier. Using a 12ga wire for the whole run is fine as well, it won't hurt anything.

The other way to do this, if there is a relay, is to eliminate the relay and route the ECM trigger to the VaporWorx blue wire. This will eliminate one more component (relay.) I believe that the GM control system comes with the fuel relay in a fuse box so figuring out which wire is the fuel pump relay enable may require some searching.

Either of the two methods above will work just fine.

[sjaroslo]

Thank you very much, Carl! As noted in the quote above from the GM Engine Controller doc, the wire is indeed fused and relayed, out of the engine controller fuse panel, as you mentioned. While I can appreciate the streamlining effort to run from ECM directly to the Vaporworx blue wire, I am not necessarily feeling that ambitious.... :scared: I think I'm good with using the fused and relayed wire as the trigger. But again, thank you for your support and for always being there supporting your Vaporworx customer base!

[CarlC]

I'm glad to help.

Just run that grey wire in your photo to the blue wire on the VaporWorx controller. It will work fine.

The reason for the blue color on the controller is that it is the same as the AAW fuel pump circuit insulation color. Unfortunately there are many different trigger colors out there so it's tough to be consistent.

[sjaroslo]

Yes, I'm planning on using dark blue to be consistent with the AAW harness, exactly.