Koer Test Goes To 3000rpm And Stays?

Discussion in 'Fox 5.0 Mustang Tech' started by JohnnyK81, Sep 18, 2013.

  1. That can't be normal.. 2 computers now (Both of unknown condition, but appear ok other than a dang code 66), when running a KOER test after reaching operating temperatures, the RPMs shoot up to 3100 or so and slowly lower to 2950 or so.. This, is very obnoxiously loud, and causes it to heat up to fast..

    Has anyone seen this before??

  2. I dont remember the test rpm, but it is supposed to shoot the rpms up during the test. But not hold it there constantly. It should vary up and down while it is running certain parts of the test. I have seen on a few occasions where certain hard faults (66 is considered a hard fault) where present during KOEO, and when the KOER test was started, it would do exactly as you described.

    Code 66 is a Low MAF voltage code. You can manually test the MAF signal wire with a voltmeter to check its voltage output at idle, to try and determine if its a MAF issue, or a wiring/bad connection issue.
  3. If you are looking to do a cylinder balance tests, here's the how to do it...

    Cylinder balance test

    If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

    Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
    Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure
  4. Well, i DO have code 66.. but I'm stumped.. I swapped computers this morning to try to fix it.. same issue (Although it did idle better?!).. But MAF voltages looked ok.. But then I tried again tonight and the MAF voltages were way off (I swear it shot up to 10 when I revved it a tiny bit!!!! And stayed around 3.. But earlier this morning it was fine.. bad MAF? That would be ideal).

    Wiring checks out fine.