1968 Shelby GT500

Injector Firing Order

Firing order does not effect spark at the plugs because that is still determined by what order you put the plug wires on the distributor cap. But if you have a sequential fire fuel injection computer, then the computer program opens the injectors in the same order as the camshaft timing. This can cause issues when running a “High-Output” computer with an older camshaft. If you leave the injectors in the HO order you might notice a slight effect on idle quality. There are no effects once the engine speed picks up because the injectors open so fast.

There are 2 ways to “correctly” fix a computers mismatched firing order:
1. The best option is to change to a HO camshaft to match the computer.
2. Or you can reprogram the computer to match the cam firing order.

<.htmlp>Other people with mismatched computers swap the injector pins at the computer plug. This causes more problems than it

An example of how the computer deals with mixed up injectors:
1. The R O2 sensor sends a rich signal to the computer.
2. The computer will then shorten the pulse width to Right side of the engine. But two of those injectors have been MOVED to the Left side of the engine!
3. Because 2 of the injectors that have been directed to minimize the injector pulse are now on the other side of the engine, this causes the left side of the engine to run lean.
4. So now the L O2 will send the lean signal to the computer.
5. The computer will then lengthen the pulse width to Left side of the engine. But two of those injectors have been MOVED to the Right side of the engine!
6. So now the R O2 sends another rich signal to the computer.
7. Cycle repeats, each time getting worse.

You end up with 1, 2, 5 & 7 running 25% rich, and 3, 4, 6 & 8 running 25% lean!
Therefore it is strongly discouraged to mix around the fuel injectors.


© 2002-2012 UNIVEX Automotive Institute.
oldfuelinjection.com, is not affiliated with Ford Motor Company."