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Brian, Auto Service Technician
Category: Ford
Satisfied Customers: 1227
Experience:  5 years Ford Technical Hotline/Service Engineer. 2005 Ford Master Cert. Automotive Technology degree
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1984 ford bronco: v8..bypass..the ecu for distributor

Customer Question

I got a 1984 ford bronco that as a 300 i6, i want to put in a 302 v8 out of 1982 ford van. My question is with this motor how do i bypass the ecu for distributor.
Submitted: 9 years ago.
Category: Ford
Expert:  Brian replied 9 years ago.
You could obtain an older style Duraspark distributor from a late 70s early 80s 302. Also, you will need the Duraspark module and a connecting wire harness. Keep the newer coil and connect it to the Duraspark module. The older distributors have an electromagnetic pickup that triggers the Duraspark module which runs the coil. The distributor would have a vacuum advance and mechanical advance that could be tuned as needed for optimal efficiency once it's running.

You could also go to the aftermarket to do this. You would need a distributor, and a module from any of the companies like MSD, Mallory, Accel, Pertronix, or others (see Summit Racing or Jeg's online catalogs for starters).

The cheapest way would be the Duraspark method. It would also be recommended to upgrade the coil to the more modern, more efficient, and stronger sparking "TFI" style coil that looks like this (if it does not already have this style coil):
There is a great page on adding Duraspsark with a TFI coil on this page:

There are pictures and wiring diagrams to help.

You can use a stock or aftermarket TFI coil.

For more info, you can search keywords "TFI coil" and "TFI upgrade" on Google.
Customer: replied 9 years ago.
but will it bypass the ecu
Expert:  Brian replied 9 years ago.

Yes the ECU is bypassed. The ignition timing advance that was electronically controlled will now be controlled entirely with the vacuum advance/mechanical advance distributor and Duraspark module. The ECU will not be needed.

Here is a picture of the overall layout for the Duraspark TFI method:




Ford Duraspark 2 Ignition System

  1. Introduction

    The Ford Duraspark II electronic ignition system will improve your throttle response, horsepower, and gas mileage over a points type system. Not to mention it is maintenance free. The Duraspark II system was used on all small blocks starting in 1977. The system will give a very hot and consistent spark good to about 350+ naturally aspirated horsepower and also works well up to about a 150 HP shot of nitrous. This article is designed to show you what pieces go together and give some tips on hooking it up.


  2. Tips and Tricks

    The ignition system is comprised of four basic components - the distributor, ignition module, the coil, and the wiring harness.

    First the distributor, the key here is to get a distributor that is compatible with your cam type, has vacuum advance, and has a decent mechanical advance curve. What this means is if your using a roller cam you need a steel gear - see the Ford Motorsport catalog or just use an '85 Mustang 5.0L GT distributor for a 5-speed. I paid about $90 for mine from the Ford dealer rebuilt. Also the '85 Mustang distributor has vacuum advance and a great advance curve straight from the factory. If you are using a flat tappet cam your first choice should be an '82-'84 5.0L Mustang HO distributor. This distributor also has vacuum advance and a good curve. In the end any '77-'84 302 distributor will work with as long as the car was carbureted (NO CFI - throttle body injection), just don't forget to use a drive gear that is compatible with your cam. Get your distributor advance recurved as follows: centrifugal advance - 0° @ 1,300 rpm, 11° @ 2,000 rpm, 20° @ 5,000 rpm; vacuum advance - 0° @ 4.5" Hg, 11.5° @ 8" Hg, 20° @ 12.5" Hg.

    Okay, so what's the big deal about vacuum advance? How about your gas mileage - with a vacuum advance distributor your gas mileage will be significantly higher than with a mechanical advance distributor alone. If it is a strip only car then it won't matter - vacuum or mechanical.

    Ignition Module - This is really pretty simple - get the one with the blue color plastic where the wires go into the module. When mounting to the fender-well be sure it is grounded good and away from high temperatures (exhaust and motor). Heat is what kills electronics so a little prevention up front will go a long way.

    The coil - Just about any coil will work but stick to the good stuff - Accel, MSD, Mallory, or Jacobs for the best results. Once again, mount on the fender-well away from heat for the longest life.

    Wiring Harness - It is always easiest to use the factory harness with the factory connections, but be careful, I have had to chase many problems due to failed factory connections, the best bet is to clip out all connections and solder wires together once you know the wiring is right. Follow the diagram below for hooking up.

diagram.jpg - 16,937 bytes


    Odds and Ends - For the distributor cap and rotor be sure to use a cap with brass terminals and large diameter (1977 or later).


Above info from: Fletch's Carbureted 5.0 Mustang site:

He also has a page about converting a Mustang from fuel injection to carburetion, worth a read, it might help you work through the conversion even though some info is Mustang specific: