Engine swap wiring conversions AKA motivation for you

Shran · May 2, 2016

For those of you considering a V8 swap (or even a 4.0, or whatever...) and are afraid of a mess of wiring and confusion, consider this:

I helped a guy that is building an offroad only rig several weeks ago and got tasked with wiring the engine. The truck is an early 80's F150 with NO wiring whatsoever, it was all removed. Engine is a 5.0 from a 91 Mustang, engine wiring harness also came out of the same car.

The goal: make it as simple as possible - how few wires does it actually take to make this run?

I spent some time going through his Mustang harness identifying wires. This was time consuming but not unfamiliar territory, as I have done my own Ranger 5.0 swap. What I found was surprising:

A fuel injected Ford engine from the mid 80's to early 90's will literally start and run with only FOUR wires. Yep! That includes two grounds, a "hot in run or start" and "hot at all times."

How motivating is that? At that point you have a running engine! Now of course that does not make other accessories work such as the fuel pump, alternator, O2 sensors AC clutch, gauges, etc that are all part of the factory harness...but it is pretty damn simple.

So there you have it, for those of you considering going with a carburetor...these things are dead simple.

Get swapping! :icon_hornsup:

alwaysFlOoReD · May 2, 2016

For those of us that are slightly "short" of a full understanding, can you tell us which four wires and where they need to be hooked up to?

Shran · May 2, 2016

alwaysFlOoReD said:
For those of us that are slightly "short" of a full understanding, can you tell us which four wires and where they need to be hooked up to?

On the 91 Mustang harness (may, and probably will, vary by year and donor vehicle) there were two black wires - one that runs directly to the negative battery post, and the other has a ring terminal on it - those are your grounds.

I believe but am not certain as I am working off memory here but red/green and red/blue, or maybe it was blue/red, were the other two. A look at a diagram would confirm but one is attached to the hot side of the starter solenoid, and the other (the "hot in start or run" wire) goes to the hot side of the ignition switch.

I was concerned about the "hot at all times" one being connected directly to power all the time but it has not drained the battery yet.

One other wire of significance was big green/yellow (fuel pump +). This one is interesting because it will energize an aftermarket fuel pump simply by powering on the ECM since the fuel pump relay and everything is all part of the same harness. Very handy.

The Mustang harness was very easy to use but 91 may not be the best year because it has a lot of extra junk like airbag crash sensors and a bunch of stuff for a speed sensor. Earlier cars don't have that stuff.

Also important to note is that since this is a race application we simply disconnected ALL of the smog stuff - including the EGR, and simply capped the vacuum lines off and left the wires loose. It had no effect on how the engine runs.

On that same note, I think it would be entirely possible and probably preferable to simply un-pin all of the smog wiring from the ECM connector and remove all of it from the harness completely, in this application, it is not needed.

RonD · May 2, 2016

Yes, some of the computers from that era used only Batch Fire fuel injection, not Sequential fuel injection.

In any Ford fuel injection system the injectors all get 12volts from EEC(PCM) relay, 1 wire daisy chained
Then with Batch Fire on a V8 4 injectors share common Ground wire from computer, 2 wires = 8 injectors
Computer alternates grounding the 2 sets of injectors, keeps intake full of air/fuel mix, one step up from carb

12volt wire for computer, 1 wire, assuming computer is grounded, another wire?

But you also need a timing signal for the computer to open injectors at correct time, even with Batch Fire, 5th wire
It can come from distributor or Crank Position sensor(distributorless) but still a needed 5th wire.

So 4 wires would be a stretch unless you don't count Grounds or computers power

And we still need something to set injector open time, pulse width, air/fuel ratio, so MAP, or MAF

Shran · May 2, 2016

When was the changeover year for sequentially fired injectors? I'm guessing it only happened on the Explorer 5.0, some late 90's V8's and modular engines? I have engines and harnesses for '96 5.8 MAF and '97 5.8 speed density, and it seemed that the injector harness was wired differently - each injector had its own power wire going to the ECM and a common ground, vs the '89 and '91 harnesses that had basically a common ground and common power for each bank.

85_Ranger4x4 · May 3, 2016

http://www.therangerstation.com/Magazine/summer2008/2_9-to_5_0-Swap.shtml

I heave read it isn't that hard, for the most part they are not far from stand alone.

If I ever get an old Mustang I have an Explorer intake waiting for it. I think I have an intact injector harness so I would just need the ECM harness.

For what my Ranger does I have no problem with the carb though. It was even plug and play from my durasparked 2.8.

adsm08 · May 3, 2016

Yeah, this stuff isn't hard.

When I put the 4.0 in my BII I repinned the 4.0 alternator plug onto the 2.9 charging spud and spliced two more wires. Everything but the reverse lights work, and that's just a matter of two more wires.

Shran · May 3, 2016

85_Ranger4x4 said:
http://www.therangerstation.com/Magazine/summer2008/2_9-to_5_0-Swap.shtml

I am pretty sure I used that as a reference when I did my 5.0 swap years ago, the only difference for me was that I used a Crown Vic harness, which looks almost identical to that one. It was also basically a standalone deal, provided that you have power and grounds hooked up in the right spots it will work great with very little effort.

bobbywalter · May 5, 2016

hmmm....i been singing that song for over 20 years

for hotrod-buggy operation i can run the eec 4 with 1 jumper wire and a quarter when its in its oem application.. when i take a running vehicle and do that in front of a person, then people are put at ease with the prospect of putting it in their project.

for a smog compliant setup complete with functioning ac and cruise control....

well that situation is slightly more complicated.

but not much.

at one point in time i could make a harness from scratch and had the pinouts memorized. when i make a stand alone harness, i usually put the check engine light and on-off and crank in one mountable box with piggy back realy leads for the fuel pump.

making sure the o2 sensor heater circuit is operational and fused is often an issue causer of wierd shit, and the old processors are getting shitty with leaking capacitors etc these days.

the pats system with the eec 5 is really the only serious complication with that for most.. much better system for tuning though.

Engine swap wiring conversions AKA motivation for you

Shran

Junk Collector

alwaysFlOoReD

Forum Staff Member

Shran

Junk Collector

RonD

Official TRS AI

Shran

Junk Collector

85_Ranger4x4

Forum Staff Member

adsm08

Senior Master Grease Monkey

Shran

Junk Collector

bobbywalter

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