Auto Electrical Forum

Automotive Electrical Tech Tips and Questions Answered

Jim Asks:
I have a modified 1987 Fiero GT.
It had a 1995 Cadillac 4.6 Northstar in it.
Question:

Fuel connector C502 in the center rear engine bay, connects to fuel tank.
Has a pink wire, a tan/white, and a black wire.
I have added a external fuel pump.
I’m ready to start motor up.
The C502 connector, shows volts when key is on.
(Fear blowing up car.)
The tan/wht wire is for the fuel pump,
which I have elimamated.
Should show voltage?
Question: should that C502 connector show voltage?
Thanks Jim

Answer:
I think this is something that others may have an interest in, so I am going to frame my answer in a generic form.
When doing an engine swap there are many things that must be accounted for in regards to fuel injection. You are most likely going to use the ECU or a modified ECU for the engine you are swapping into the vehicle. Now lets look at the obvious, the fuel lines should be the same size, keep in mind we need to move the same volume of fuel not just the same fuel pressure.
Next does the new engine have a fuel pump control module or is it a simple relay control. If it is a relay design then the wiring is easy, just replicate the wiring and you are ready to do. If the new ECU has a fuel pump control circuit, internal or external, it must be inspected carefully. You can just wire it in because it may have “G” sensor circuitry, this will adjust pressure based on what the vehicle is doing, keep in mind a Cadillac will not corner the same as a Fiero. A mistake here can cause over rich or lean out during cornering or under accretion or deceleration. You may be better eliminating the controller and this will require duplicating the ECU inputs so the ECU will not trip a code or go into “limp home”.
This is how I normally wire it in, step one check the wiring to determine if the ECU controls ground or voltage. Most ECU’s supply the ground for the fuel pump and the voltage is supplied when the key is turned on. To play it safe I will run a relay, the ECU controls the low current side and the battery supplies voltage to the fuel pump and ground is run through the relay.
Finally make sure your fuel pump can make the specs of the engine you are swapping in. Now a hot tip, if this is a daily driver with some part time racing, check out our adjustable external regulator. With this you can run 14 volts when not racing but turn the voltage up to 16 – 17 volts when racing, the fuel pump will supply all the fuel you will ever need at 16.5 volts. We have seen .5 sec to a full second gain in the quarter mile.

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