I'm going to be removing a Motorcraft 2150 carburetor in a 2.8L V6 and swapping it for a Ford CFI (and ECU) from a 3.8L V6. I've just recently pulled everything (ECU, throttle body, sensors, harnesses, etc) from a Mercury Cougar.

When I was removing the CFI from the Cougar, I've noticed that the EEC-IV harness has two inputs for the heated O2 sensors (one in each manifold), but the 2.8L only has one O2 sensor (around the driver's side manifold).

  • Is there a way to connect both O2 sensor inputs to a single O2 sensor? Or do I need to take off the other manifold and tap a hole into it?

  • If I can connect both inputs to a single sensor, would it make any difference in the performance of it? Could the EEC-IV & CFI even make adjustments for each "side" of the engine? It does have separate injectors, but it seems like the air-fuel mixture would get combined in the intake after the CFI.

  • 1
    There is a lot of expense (from the point of view of an auto industry engineer and/or bean counter) in an extra O2 sensor and its support in the ECU, so I'd think that it is very likely that it does something useful.
    – dlu
    Jul 28, 2016 at 0:07
  • I suspect the dual O2 sensors are the least of your problems. Even on a speed-density system, something has to rewrite the EEC-IV fuel maps to compensate for the loss of 1 liter of displacement. Has somebody already done this conversion and you are following that lead? It's one thing to swap CFI out for a carb on a Mustang 302. Yet quite another to lose 25% of the displacement and hope the EEC will learn and compensate.
    – SteveRacer
    Jul 28, 2016 at 2:02

1 Answer 1


Drill and tap the other manifold, or have a good welder braze or weld an O2 bung somewhere accessible. However, please see my comments above... maybe I can improve this answer.

This sounds like a cool project, and I don't want to discourage it, but there may be more than just mounting the throttle body and expecting correct Air/Fuel ratios without ECU (EEC-IV) remapping. Possibly you could fudge a little with coolant temp sensor resistors and possibly throttle position sensor... but I doubt a manifold pressure drop of say, 2psi on the 2.8 equates to the same CFM (and needed fuel injection) as the 3.8 mapping. I could be wrong, if the intake manifold configuration is very similar.

Just keep in mind that a 25% reduction in displacement translates to a 25% reduction in airflow CFM for any given RPM. The airflow is calculated from the signal of pressure drop of the MAP (manifold pressure sensor) and is only valid for that particular manifold. The information is scaled in the EEC-IV along with RPM and throttle position, to determine the proper fuel injector (in your case central, single-point) pulse width.

None of that was an answer to your original question... but I'd rather not send you down a path if there are other monsters to be slayed first.


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