Wiring, grounds, and relays

[vabeachsand]

So I am using a entire PCM and harness from a 99 cobra. My question is that I am assuming I can just wire the fuel pump relay trigger wire to like pin 14 on the plug that is supposed to go the the harness for the FPDM? This way it primes for 2 seconds then runs full when the car is on.

I am assuming the EEC is getting power from the main harness, so all I have left to do is repin the ignition wiring and then turn the key.

Also, I am running the stock alternator charge wire as a chassis ground, and a 2 guage wire straight from the alternator to a solenoid / battery junction block for the battery mounted in the trunk. Would this be okay?

 

[FuturaGuy]

Before anyone can help you, we need to know more about how you're doing the wiring. How much of the original wiring are you keeping and how are you connecting it to the Cobra PCM harness? You are correct in saying that the EEC gets its power thru the main harness, but the power comes from 2 different sources. It's fed from the underhood fuse box and also from the ignition switch. When you talk of Pin 14, which connector is it in? The PCM harness, when you're looking at it, seems to have a hundred connectors. That's an exaggeration, but not much of one.

If you can make a sketch of what you did, that will help us answer some of your questions.

 

[vabeachsand]

I am trying to splice the fox fuel pump relay into the 99 dash harness. I understand that on the 99 cobras and other 96+ cars; that the fuel pump is driven by a electronic module in the trunk area (FPDM). I have a external fuel pump going to a fuel cell that is hooked into the factory fuel pump wiring from my 89.

The relay in my 89 fox car is under the driver's seat, and I have wired the positive connection to the battery, via a 16 gauge fusable link. (Pin 3 on the relay connector.



http://modularfoxmustangs.com/community/attachments/46_in_fox_wiring-pdf.662/

The above document mentions that pin 8 grounds the fuel pump relay and pin 14 provides fuel pump power.
My idea was to run pin 14 on the c200 connector (cobra harness) to pin 2 (fox fuel pump relay) and the same with pin 8 (cobra harness) to pin 1 (fox fuel pump relay) to energize it. And of course Pin 4 on the relay should go to the fuel pump.


FOX Fuel pump relay pinout.

Cobra FPDM diagram

C200 connector on passenger side kick pannel by EEC

And here is a picture of my fuel pump setup. Its just externally mounted and wired to the original fox wiring in its stock location.

I hope this explains things a little better.

 

[FuturaGuy]

Good diagrams and description. I'll have to spend some quality time studying this before I can answer your questions. Don't want to give out bad information.

 

[Bill]

Good diagrams and description. I'll have to spend some quality time studying this before I can answer your questions. Don't want to give out bad information.

Oh come on. This isn't Corral.net. No one here would give out bad information

 

[FuturaGuy]

Oh come on. This isn't Corral.net. No one here would give out bad information

Not intentionally, but one must remember Murphy's Law and that Murphy was an optimist. Therefore, when I post any technical information here, I want to be sure it's right.

 

[vabeachsand]

I went ahead and wired pin 1 to the relay, and then just grounded the other side to the chassis. It seems to work fine but I will have to monitor the voltage the verify it stays constant.

 

[vabeachsand]

Just a update. I am having issues with the car idling in this configuration. I will plan on removing this from the FPDM trigger wire and powering the relay via a spst kill switch.

 

[1982mustangIa]

The research that I've done has led to finding out that the "trigger" wire from the pcm doesn't have enough voltage/amperage to properly trigger your relay, the solution that some have used and the method I will be using is using the output both positive and ground from the FPDM itself to trigger the the relay.

 

[vabeachsand]

This is excactly what is happening with my car. If you are running a return style fuel setup use a manual switch or a relay setup triggered by the hot in run wire under the ignition column. You could also pin it off of the fuse box as well.

 

[cpearson1342]

I tried to wire up my fuel pump straight to the 03' mach computer and it would not work for whatever reason, I think it was giving the wrong type of voltage, (positive instead of negative or something like that) If you had a fuel pump driver module I'm almost sure you have to use it, especially if you are staying returnless or the fuel pressure will be way too hight, I may have missed you saying if you were or not but I was just skimming the thread

 

[vabeachsand]

I am using a return style setup. Fuel pressure is regulated by my aeromotive fpr. I have my tune set to a static value of 60 psi.